Blueprints. Installing Linux on a Multipath iscsi LUN on an IP Network

Transcription

1 Blueprints Installing Linux on a Multipath iscsi LUN on an IP Network

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3 Blueprints Installing Linux on a Multipath iscsi LUN on an IP Network

4 Note Before using this information and the product it supports, read the information in Notices on page 27. First Edition (August 2009) Copyright IBM Corporation US Government Users Restricted Rights Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp.

5 Contents Introduction v Chapter 1. Scope, requirements, and support Chapter 2. iscsi and Multipath overview 3 Chapter 3. Installing Linux distributions on multipathed iscsi target devices.. 5 Installing RHEL5.3 on a multipath iscsi storage device Installing SLES 11 on a multipath iscsi storage device (System x only) Chapter 4. Troubleshooting tips iscsi and Multipath overview Installing Linux distributions on multipathed iscsi target devices Installing RHEL5.3 on a multipath iscsi storage device Installing SLES 11 on a multipath iscsi storage device (System x only) Troubleshooting tips Appendix. Related information and downloads Notices Trademarks Chapter 5. Installing Linux on a Multipath iscsi LUN on an IP Network. 15 Scope, requirements, and support Copyright IBM Corp iii

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7 Introduction This blueprint provides step by step instructions for installing Red Hat Enterprise Linux (RHEL) 5.3 and SUSE Linux Enterprise Server (SLES) 11 on a Multipath iscsi Logical Unit (LUN). The procedures are tested on a System x and a System p blades connected to a NETAPP storage server through an Ethernet IP network. You can adapt these instructions to install either of these Linux distributions onto other supported models of iscsi storage devices. Key tools and technologies discussed in this demonstration include ISCSI logical unit (LUN), device mapper (DM) multipath, multipathed iscsi, iscsiadm, and dmsetup. Intended audience This document is intended for Linux system administrators who have prior experience in installing Red Hat Enterprise Linux 5 or SUSE Linux Enterprise Server 11 and have a moderate level of knowledge in Device Mapper (DM) Multipath and iscsi. Scope and purpose This document provides installation steps of RHEL5.3 and SLES11 to a System x or System p host that is connected to a iscsi storage device through an IP network. The instructions may change in newer releases of the same distributions. The configuration and setup of the host and the iscsi storage device and the physical setup of multiple paths to this storage device are not covered in this document. Refer to the documentation supplied with your storage device for more information. The instructions in this blueprint were tested on System x and System p blades. The instructions should work on System x and System p non-blades with some adaptation. In addition, the instructions assume installation of RHEL 5.3 or SLES 11 onto the multipath iscsi boot device. Part of the instructions should work even if you want to only setup the multipath on iscsi non-boot device. Software requirements This blueprint is written for Red Hat Enterprise Linux (RHEL) 5.3 and SUSE Linux Enterprise Server (SLES) 11. Hardware requirements See the IBM Storage interoperability matrices at interop.html for supported storage configurations. The examples included in this blueprint are tested on a System x LS21 blade and a System p JS12 blade host system with one network adapter. The iscsi storage target is a NetApp dual-node file server with two logical units. Author names Malahal Naineni Other contributors Monza Lui Robb Romans Kersten Richter Copyright IBM Corp v

8 IBM Services Linux offers flexibility, options, and competitive total cost of ownership with a world class enterprise operating system. Community innovation integrates leading-edge technologies and best practices into Linux. IBM is a leader in the Linux community with over 600 developers in the IBM Linux Technology Center working on over 100 open source projects in the community. IBM supports Linux on all IBM servers, storage, and middleware, offering the broadest flexibility to match your business needs. For more information about IBM and Linux, go to ibm.com/linux ( IBM Support Questions and comments regarding this documentation can be posted on the developerworks Storage Connectivity Blueprint Community Forum: The IBM developerworks discussion forums let you ask questions, share knowledge, ideas, and opinions about technologies and programming techniques with other developerworks users. Use the forum content at your own risk. While IBM will attempt to provide a timely response to all postings, the use of this developerworks forum does not guarantee a response to every question that is posted, nor do we validate the answers or the code that are offered. Typographic conventions The following typographic conventions are used in this Blueprint: Bold Italics Monospace Identifies commands, subroutines, keywords, files, structures, directories, and other items whose names are predefined by the system. Also identifies graphical objects such as buttons, labels, and icons that the user selects. Identifies parameters whose actual names or values are to be supplied by the user. Identifies examples of specific data values, examples of text like what you might see displayed, examples of portions of program code like what you might write as a programmer, messages from the system, or information you should actually type. Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. vi Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

9 Chapter 1. Scope, requirements, and support This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Systems to which this information applies System x running Linux and PowerLinux Copyright IBM Corp

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11 Chapter 2. iscsi and Multipath overview The iscsi standard (RFC 3720) defines transporting of the SCSI protocol over a TCP/IP network that allows block access to target devices. A host connection to the network can be provided by a iscsi host bus adapter or a iscsi software initiator that uses the standard network interface card in the host. For more information, see RFC 3720 at The connection from the server through the Host Bus Adapter (HBA) to the storage controller is referred as a path. Within the context of this blueprint, multipath connectivity refers to a system configuration where multiple connection paths exist between a server and a storage unit (Logical Unit (LUN)) within a storage subsystem. This configuration can be used to provide redundancy or increased bandwidth. Multipath connectivity provides redundant access to the storage devices, for example, to have access to the storage device when one or more of the components in a path fail. Another advantage of using multipath connectivity is the increased throughput by way of load balancing. Note that multipathing protects against the failure of path(s) and not the failure of a specific storage unit. A simple example of multipath connectivity is two NICs connected to a network to which the storage controllers are connected. In this case, the storage units can be accessed from either of the NICs and hence you have multipath connectivity. In the following diagram, each host has two NICs and each storage unit has two controllers. With the given configuration setup, each host will have four paths to each of the LUNs in each of the storage devices. Copyright IBM Corp

12 Figure 1. Simple IP network example Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. 4 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

13 Chapter 3. Installing Linux distributions on multipathed iscsi target devices Use these instructions to install RHEL 5.3 or SLES 11 distribution to logical volumes created from two physical iscsi storage devices. Before beginning, complete the physical configuration of the multipath servers to the iscsi storage. Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Installing RHEL5.3 on a multipath iscsi storage device Follow these steps to install Red Hat Enterprise Linux 5.3 on a multipath iscsi storage device. Procedure 1. To install RHEL 5.3 on an iscsi LUN, follow the steps in the iscsi Overview blueprint at Adjust the following step to prepare for the multipath creation after the installation: Add the mpath parameter at the boot prompt during installation. For example, instead of using the command linux vnc, this blueprint used linux mpath vnc command in the test environment. This demonstration assumes the default LVM partitioning scheme. If you want to install RHEL 5.3 onto a different partitioning scheme, adjust the steps. 2. Check that your root file system image is discovered as installed on a multipath iscsi device. If it is, then you have completed all required steps and no further multipath configuration is necessary. Otherwise, continue with the next step. a. Enter the mount command to find where the root file system image is located. The following output shows that root is on the logical volume VolGroup00/LogVol00: # mount /dev/mapper/volgroup00-logvol00 on / type ext3 (rw,_netdev) proc on /proc type proc (rw) sysfs on /sys type sysfs (rw) devpts on /dev/pts type devpts (rw,gid=5,mode=620) tmpfs on /dev/shm type tmpfs (rw) none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw) sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw) /dev/sda1 on /boot type ext3 (rw,_netdev) b. Enter the lvs -o lv_name,vg_name,devices command to check where this logical volume resides. If the output is similar to the following output (which shows that the root file system image is located on devices named /dev/sdx), then the root file system image is detected through single path devices. In the following output, the root file system image is detected on /dev/sda2 and /dev/sdb1 which are not multipath devices. If your root file system image is detected on single path devices as below, go to step 3. # lvs -o lv_name,vg_name,devices LV VG Devices LogVol00 VolGroup00 /dev/sdb1(0) LogVol00 VolGroup00 /dev/sda2(0) LogVol01 VolGroup00 /dev/sda2(31) On the other hand, if you see something like the following output (which shows that the root file system image is on devices named /dev/dm-x), gather more information to see if the DM device is a multipath device. Copyright IBM Corp

14 # lvs -o lv_name,vg_name,devices LV VG Devices LogVol00 VolGroup00 /dev/dm-2(0) LogVol00 VolGroup00 /dev/dm-4(0) LogVol01 VolGroup00 /dev/dm-4(31) c. Enter the command ls -l on both DM devices to find their major and minor numbers: # ls -l /dev/dm-2 brw-rw root root 253, 2 Jul 14 14:30 /dev/dm-2 # ls -l /dev/dm-4 brw-rw root root 253, 4 Jul 14 14:30 /dev/dm-4 d. Enter the dmsetup command with the major and minor numbers as parameters to see if they are multipath devices. If they are, determine the corresponding mpath names. The following output shows that /dev/dm-2 and /dev/dm-4 correspond to mpath1p1 and mpath0p2. If they are, then this root file system image is installed on a multipath iscsi LUN. # dmsetup info -c -o name,major,minor --major minor 2 Name Maj Min mpath1p # dmsetup info -c -o name,major,minor --major minor 4 Name Maj Min mpath0p The multipath -ll command shows you that mpath0 and mpath1 are multipath devices with two paths each, as follows: # multipath -ll mpath1 (360a f68656c6f ) dm-1 NETAPP,LUN [size=7.0g][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=4][active] \_ 0:0:0:1 sdb 8:16 [active][ready] \_ 1:0:0:1 sdd 8:48 [active][ready] mpath0 (360a f68656c6f f) dm-0 NETAPP,LUN [size=5.0g][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=4][active] \_ 0:0:0:0 sda 8:0 [active][ready] \_ 1:0:0:0 sdc 8:32 [active][ready] If you see similar output, you are finished because the multipath setup was performed automatically. No further multipath configuration is necessary. If you do not see similar output, continue to the next step. 3. Create multiple iscsi sessions (multiple paths) a. Enter the command ls -d /sys/block/sd* to see how many block devices are found by the initrd image created by the installer, as follows: # ls -d /sys/block/sd* /sys/block/sda /sys/block/sdb b. Enter the command iscsiadm -m node --login to find other iscsi paths: # iscsiadm -m node --login Logging in to [iface: default, target: iqn com.netapp:sn , portal: ,3260] Logging in to [iface: default, target: iqn com.netapp:sn , portal: ,3260] Login to [iface: default, target: iqn com.netapp:sn , portal: ,3260]: successful iscsiadm: Could not login to [iface: default, target: iqn com.netapp:sn , portal: ,3260]: iscsiadm: initiator reported error (15 - already exists) c. You should see extra device paths in the /sys/block/ directory after running the above command. These devices are newly-created iscsi paths. In this example, the newly-discovered iscsi paths are sdc and sdd, as follows: 6 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

15 # ls -d /sys/block/sd* /sys/block/sda /sys/block/sdb /sys/block/sdc /sys/block/sdd 4. Edit the /etc/multipath.conf file. a. Ensure that the file contains the following line: defaults { user_friendly_names yes } b. Multipath-tools blacklist everything listed within the blacklist {} statement contained in the /etc/multipath.conf file. Comment out the wwid line within the blacklist {} statement so that the iscsi devices are not blacklisted. For example, here is a modified multipath.conf file: # cat /etc/multipath.conf defaults { user_friendly_names yes } blacklist { devnode "^(ram raw loop fd md dm- sr scd st)[0-9]*" devnode "^(hd xvd vd)[a-z]*" # wwid "*" } 5. Enter the multipath command to create a bindings file named /var/lib/multipath/bindings. This file is included in the new initrd image. # multipath 6. Edit /etc/fstab file to ensure it doesn't have single path device names or LABELs The /etc/init.d/netfs script may try to mount single path names (such as /dev/sda1) because the label is the same on a single path device as well as its corresponding multipath device name. However, the script cannot mount the device because the corresponding multipath device is already active. To avoid this error during boot, edit the /etc/fstab file and replace any LABELs or path names with LVM names or multipath names, as appropriate. See the next step for an example. In this example, the default LVM partitioning scheme was accepted during system installation so the /etc/fstab file on the test system contains the following LABEL entry: LABEL=/boot / boot ext3 defaults,_netdev 1 2 a. Find out which multipath device corresponds to /boot LABEL. Enter the blkid -l -t LABEL=/boot command to determine which device has /boot LABEL. The following output shows that /dev/sda1 has /boot LABEL: # blkid -t LABEL=/boot /dev/sda1: LABEL="/boot" UUID="cec3f5e afb-a3fec0b40ccb4420" SEC_TYPE="ext2" TYPE="ext3" b. Determine the wwid (World Wide IDentifier, a unique identifier for a logical unit in a SCSI storage subsystem) of the boot device (/dev/sda in this example) by typing the following command: # /sbin/scsi_id -g -u -s /block/sda 360a f68656c6f f c. Determine the boot device's mpath name by looking at the /var/lib/multipath/bindings bindings file. In our bindings file, the wwid of sda corresponds to mpath0: # cat /var/lib/multipath/bindings # Multipath bindings, Version : 1.0 # NOTE: this file is automatically maintained by the multipath program. # You should not need to edit this file in normal circumstances. # # Format: # alias wwid # mpath0 360a f68656c6f f mpath1 360a f68656c6f Chapter 3. Installing Linux distributions on multipathed iscsi target devices 7

16 d. In general, multipath device names take the form of /dev/mapper/mpathxpy, where X is the multipath number and Y is the partition number. From the previous step, mpath0 corresponds to /dev/sda. Therefore, you can translate /dev/sda1 to /dev/mapper/mpath0p1 and replace the LABEL=/boot with the multipath device name of /dev/sda1: /dev/mapper/mpath0p1. Here is the new entry for the boot device in the /etc/fstab file: /dev/mapper/mpath0p1 /boot ext3 defaults,_netdev 1 2 It replaces the old entry: LABEL=/boot /boot ext3 defaults,_netdev 1 2 Note: If you choose to not to use friendly names in step 4.a, you need to use this format: /dev/mapper/<wwid>p<partition number> for the multipath device names. For example, here is an entry in /etc/fstab for /boot without friendly names: /dev/mapper/360a f68656c6f fp1 /boot ext3 defaults,_netdev Create an iscsi/multipath capable initrd image by following these steps: a. Save the original /sbin/mkinitrd and /boot/initrd image files for backup. Enter the following commands to create backup files: # cp /sbin/mkinitrd /sbin/mkinitrd.orig # cp /boot/initrd el5.img /boot/initrd el5.img.orig b. Edit the /sbin/mkinitrd file. Open the file and search for the findstoragedriver () function. The arguments passed to findstoragedriver () are not correct for the default LVM installation. Typing ls -d /sys/block/sd* shows you all paths. Replace the $@ in the first line of findstoragedriver() function definition with your list of all boot and root device paths. On the test system, there are two disks with two paths per disk, for a total of four path names. Therefore, change the for loop from: for device in $@ ; do to: for device in sda sdb sdc sdd; do c. Enable multipath in the mkinitrd script. Search within the /sbin/mkinitrd file for use_multipath=0, and change it to use_multipath=1. On the test system, this definition is on line d. Because your specific devices are not going to be listed in the initrd image created by the default /sbin/mkinitrd script, you must add them to the correct place in the script. Search for "echo Creating multipath devices" in the file. On the test system, this definition was found on line For each of your multipath disks, add a line such as the following example after the echo command: emit "/bin/multipath -v 0 <wwid>" For example, on the test system, these two lines were added to the /sbin/mkinitrd file: emit "/bin/multipath -v 0 360a f68656c6f f" emit "/bin/multipath -v 0 360a f68656c6f " To show the changes that we made, here is a comparison between the original and the modified mkinitrd file: # diff -Nau /sbin/mkinitrd.orig /sbin/mkinitrd --- /sbin/mkinitrd.orig :29: /sbin/mkinitrd ,7 } findstoragedriver () { - for device in $@ ; do + for device in sda sdb sdc sdd ;do case " $handleddevices " in *" $device "*) continue -1222,7 echo $NONL "$@" >> $RCFILE } 8 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

17 -use_multipath=0 +use_multipath=1 use_emc=0 use_xdr=0 if [ -n "$testdm" -a -x /sbin/dmsetup -a -e /dev/mapper/control ]; -1666,6 if [ "$use_multipath" == "1" ]; then emit "echo Creating multipath devices" + emit "/bin/multipath -v 0 360a f68656c6f f" + emit "/bin/multipath -v 0 360a f68656c6f " for wwid in $root_wwids ; do emit "/bin/multipath -v 0 $wwid" done e. Use the modified mkinitrd script to create a new initrd image: # mkinitrd -f /boot/initrd-$(uname -r).img $(uname -r) f. Reboot your system: # reboot 8. After the system reboots, the root file system image should be discovered on multpath iscsi devices. Repeat the instructions in step 2 to verify. 9. To ensure that these changes persist even if you change the storage environment, follow these steps: a. Restore the original mkinitrd that you saved in step 8.1: # cp /sbin/mkinitrd.orig /sbin/mkinitrd b. Edit /etc/sysconfig/mkinitrd/multipath file and change MULTIPATH=no to MULTIPATH=yes. If this file does not exist on your system, create the file by entering the following command: echo "MULTIPATH=yes" > /etc/sysconfig/mkinitrd/multipath Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Installing SLES 11 on a multipath iscsi storage device (System x only) The following steps are currently supported in System x only. Procedure 1. Follow all the steps in the iscsi Overview blueprint at lnxinfo/v3r0m0/topic/liaai/iscsi/liaaiiscsi.htm to install SLES 11 on an iscsi LUN. The following steps are needed once you have completed the installation and your system has rebooted. 2. Enable Multipath services at system startup by entering the following commands: # chkconfig boot.multipath on # chkconfig multipathd on 3. Create the /etc/multipath.conf file. The default SLES 11 installation does not create the /etc/multipath.conf file. See the /usr/share/doc/packages/multipath-tools/ directory for more information. In that directory, refer to the multipath.conf.synthetic template and the multipath.conf.annotated HOWTO. In the test environment, the multipath.conf.synthetic file was copied to the /etc/multipath.conf file. To do so, enter the following command: # cp /usr/share/doc/packages/multipath-tools\ /multipath.conf.synthetic /etc/multipath.conf Chapter 3. Installing Linux distributions on multipathed iscsi target devices 9

18 All entries in the example file are commented. You can change the values in this file if necessary for your environment. 4. Enter the iscsiadm -m discovery -t sendtargets -p <target node ip address>:<target port> command to add the node records that were not discovered during installation. In this example, there are two target nodes ( and with the default iscsi target port 3260) # iscsiadm -m discovery -t sendtargets -p : :3260,1001 iqn com.netapp:sn :3260,1000 iqn com.netapp:sn # iscsiadm -m discovery -t sendtargets -p : :3260,1001 iqn com.netapp:sn :3260,1000 iqn com.netapp:sn Enter the iscsiadm -m node -p <target node ip address>:<target port> -T <target IQN> -o update -n node.startup -v onboot command to set each node to start up onboot. Note that the test target IQN is iqn com.netapp:sn # iscsiadm -m node -p :3260 -T iqn com.netapp:sn \ -o update -n node.startup -v onboot # iscsiadm -m node -p :3260 -T iqn com.netapp:sn \ -o update -n node.startup -v onboot 6. Enter the iscsiadm -m node -p <target node ip address>:<target port> -T <target IQN> -o update -n node.conn\[0\].startup -v onboot command to set each node connection to start up onboot # iscsiadm -m node -p :3260 -T iqn com.netapp:sn o update -n node.conn\[0\].startup -v onboot # iscsiadm -m node -p :3260 -T iqn com.netapp:sn o update -n node.conn\[0\].startup -v onboot 7. Verify that the host system can now find all iscsi paths required for booting a. Enter the ls -d /sys/block/sd* command to see how many block devices are found by the initrd image created by the installer, as follows: # ls -d /sys/block/sd* /sys/block/sda /sys/block/sdb b. Enter the iscsiadm -m node --login command to find other iscsi paths: # iscsiadm -m node --login Logging in to [iface: default, target: iqn com.netapp:sn , portal: ,3260] Logging in to [iface: default, target: iqn com.netapp:sn , portal: ,3260] Login to [iface: default, target: iqn com.netapp:sn , portal: ,3260]: successful iscsiadm: Could not login to [iface: default, target: iqn com.netapp:sn , portal: ,3260]: iscsiadm: initiator reported error (15 - already exists) c. You should see extra device paths in the /sys/block/ directory after running the above command. These devices are newly-created iscsi paths. In this example, the newly-discovered iscsi paths are sdc and sdd, as follows: # ls -d /sys/block/sd* /sys/block/sda /sys/block/sdb /sys/block/sdc /sys/block/sdd 8. Create a multipath-capable initrd image a. Edit the /etc/sysconfig/kernel file to add dm-multipath to INITRD_MODULES keyword. If your storage configuration requires additional multipath modules, add them here as well. On the test system, only dm-multipath was added, as the storage NetApp File server did not need additional kernel modules. Here is a comparison between the original and modified file on the test system: # diff -Nau /etc/sysconfig/kernel.orig /etc/sysconfig/kernel --- /etc/sysconfig/kernel.orig :46: /etc/sysconfig/kernel ,7 # ramdisk by calling the script "mkinitrd" # (like drivers for scsi-controllers, for lvm or reiserfs) # 10 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

19 -INITRD_MODULES="processor thermal fan jbd ext3 edd" +INITRD_MODULES="dm-multipath processor thermal fan jbd ext3 edd" ## Type: string ## Command: /sbin/mkinitrd b. Create a backup copy of your initrd file c. Run the mkinitrd command to create an initrd image: # mkinitrd 9. Update your boot loader configuration with the new initrd, if needed. During the test, the original initrd file was overwritten, so the boat loader configuration file did not require updating. 10. Reboot with the new initrd image and verify that your root is on multipath. a. Use the mount command to find where the root is. The following output shows that root is on the device mapper (DM) device /dev/dm-3: # mount /dev/dm-3 on / type ext3 (rw,acl,user_xattr) /proc on /proc type proc (rw) sysfs on /sys type sysfs (rw) debugfs on /sys/kernel/debug type debugfs (rw) udev on /dev type tmpfs (rw) devpts on /dev/pts type devpts (rw,mode=0620,gid=5) fusectl on /sys/fs/fuse/connections type fusectl (rw) securityfs on /sys/kernel/security type securityfs (rw) b. Enter the ls -l command on the DM device to find its major and minor numbers. The following output shows that /dev/dm-3's major number is 253 and minor number is 3: # ls -l /dev/dm-3 brw-rw root disk 253, 3 Jul 26 16:13 /dev/dm-3 c. Enter the dmsetup table command with the major and minor numbers as parameters to look at the current table of the device. The following output shows that /dev/dm-3 is a linear mapping (partition) on DM devices whose major number is 253 and minor number is 0: # dmsetup table --major minor linear 253: d. Enter the dmsetup info command with the major and minor numbers we get from the last step, 253 and 0 in this example, to get the device name. This output shows that the suspected multipath device name is 360a f68656c6f f. # dmsetup info -c -o name,major,minor --major minor 0 Name Maj Min 360a f68656c6f f e. Enter the multipath -ll command with the device name as parameter. Check if multiple paths are discovered. In this output, two paths are shown under device 360a f68656c6f f: sda and sdc. If you see similar output, the multipath setup is complete. # multipath -ll 360a f68656c6f f 360a f68656c6f f dm-0 NETAPP,LUN [size=5.0g][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=4][active] \_ 0:0:0:0 sda 8:0 [active][ready] \_ 1:0:0:0 sdc 8:32 [active][ready] Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Chapter 3. Installing Linux distributions on multipathed iscsi target devices 11

20 12 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

21 Chapter 4. Troubleshooting tips This topic discusses troubleshooting tips and caveats. The host blade installed when testing this blueprint has two network adapters. Configuring the eth0 interface for iscsi was unsuccessful. The BIOS failed to log in to the target. Configuring the eth1 interface for iscsi was successful. Make sure that the /etc/fstab has correct LVM or multipath names because /etc/init.d/netfs tries to mount all net devices. A LABEL in the /etc/fstab file for a network device causes problems because the script tries to use underlying devices rather than a multipath device. Use only by-id names in the /etc/fstab file for the SLES 11 distribution. Both SLES 11 and RHEL 5.3 x86_64 Xen kernels failed to boot from the iscsi boot device. However, physical machine installations for both distributions were successful. SLES 11 non-xen default kernels also failed to boot from iscsi boot device with our network installation. When the ip=* parameter was removed from the grub menu, the kernel booted fine. The failsafe kernel booted normally in either case. SLES 11 cannot boot even to rescue mode if the target iqn wasn't set to onboot mode (automatic as suggested in the iscsi paper for SLES 10 Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Copyright IBM Corp

22 14 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

23 Chapter 5. Installing Linux on a Multipath iscsi LUN on an IP Network Scope, requirements, and support This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Systems to which this information applies System x running Linux and PowerLinux iscsi and Multipath overview The iscsi standard (RFC 3720) defines transporting of the SCSI protocol over a TCP/IP network that allows block access to target devices. A host connection to the network can be provided by a iscsi host bus adapter or a iscsi software initiator that uses the standard network interface card in the host. For more information, see RFC 3720 at The connection from the server through the Host Bus Adapter (HBA) to the storage controller is referred as a path. Within the context of this blueprint, multipath connectivity refers to a system configuration where multiple connection paths exist between a server and a storage unit (Logical Unit (LUN)) within a storage subsystem. This configuration can be used to provide redundancy or increased bandwidth. Multipath connectivity provides redundant access to the storage devices, for example, to have access to the storage device when one or more of the components in a path fail. Another advantage of using multipath connectivity is the increased throughput by way of load balancing. Note that multipathing protects against the failure of path(s) and not the failure of a specific storage unit. A simple example of multipath connectivity is two NICs connected to a network to which the storage controllers are connected. In this case, the storage units can be accessed from either of the NICs and hence you have multipath connectivity. In the following diagram, each host has two NICs and each storage unit has two controllers. With the given configuration setup, each host will have four paths to each of the LUNs in each of the storage devices. Copyright IBM Corp

24 Figure 2. Simple IP network example Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Installing Linux distributions on multipathed iscsi target devices Use these instructions to install RHEL 5.3 or SLES 11 distribution to logical volumes created from two physical iscsi storage devices. Before beginning, complete the physical configuration of the multipath servers to the iscsi storage. Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Installing RHEL5.3 on a multipath iscsi storage device Follow these steps to install Red Hat Enterprise Linux 5.3 on a multipath iscsi storage device. 16 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

25 Procedure 1. To install RHEL 5.3 on an iscsi LUN, follow the steps in the iscsi Overview blueprint at Adjust the following step to prepare for the multipath creation after the installation: Add the mpath parameter at the boot prompt during installation. For example, instead of using the command linux vnc, this blueprint used linux mpath vnc command in the test environment. This demonstration assumes the default LVM partitioning scheme. If you want to install RHEL 5.3 onto a different partitioning scheme, adjust the steps. 2. Check that your root file system image is discovered as installed on a multipath iscsi device. If it is, then you have completed all required steps and no further multipath configuration is necessary. Otherwise, continue with the next step. a. Enter the mount command to find where the root file system image is located. The following output shows that root is on the logical volume VolGroup00/LogVol00: # mount /dev/mapper/volgroup00-logvol00 on / type ext3 (rw,_netdev) proc on /proc type proc (rw) sysfs on /sys type sysfs (rw) devpts on /dev/pts type devpts (rw,gid=5,mode=620) tmpfs on /dev/shm type tmpfs (rw) none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw) sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw) /dev/sda1 on /boot type ext3 (rw,_netdev) b. Enter the lvs -o lv_name,vg_name,devices command to check where this logical volume resides. If the output is similar to the following output (which shows that the root file system image is located on devices named /dev/sdx), then the root file system image is detected through single path devices. In the following output, the root file system image is detected on /dev/sda2 and /dev/sdb1 which are not multipath devices. If your root file system image is detected on single path devices as below, go to step 3. # lvs -o lv_name,vg_name,devices LV VG Devices LogVol00 VolGroup00 /dev/sdb1(0) LogVol00 VolGroup00 /dev/sda2(0) LogVol01 VolGroup00 /dev/sda2(31) On the other hand, if you see something like the following output (which shows that the root file system image is on devices named /dev/dm-x), gather more information to see if the DM device is a multipath device. # lvs -o lv_name,vg_name,devices LV VG Devices LogVol00 VolGroup00 /dev/dm-2(0) LogVol00 VolGroup00 /dev/dm-4(0) LogVol01 VolGroup00 /dev/dm-4(31) c. Enter the command ls -l on both DM devices to find their major and minor numbers: # ls -l /dev/dm-2 brw-rw root root 253, 2 Jul 14 14:30 /dev/dm-2 # ls -l /dev/dm-4 brw-rw root root 253, 4 Jul 14 14:30 /dev/dm-4 d. Enter the dmsetup command with the major and minor numbers as parameters to see if they are multipath devices. If they are, determine the corresponding mpath names. The following output shows that /dev/dm-2 and /dev/dm-4 correspond to mpath1p1 and mpath0p2. If they are, then this root file system image is installed on a multipath iscsi LUN. # dmsetup info -c -o name,major,minor --major minor 2 Name Maj Min mpath1p # dmsetup info -c -o name,major,minor --major minor 4 Name Maj Min mpath0p Chapter 5. Installing Linux on a Multipath iscsi LUN on an IP Network 17

26 The multipath -ll command shows you that mpath0 and mpath1 are multipath devices with two paths each, as follows: # multipath -ll mpath1 (360a f68656c6f ) dm-1 NETAPP,LUN [size=7.0g][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=4][active] \_ 0:0:0:1 sdb 8:16 [active][ready] \_ 1:0:0:1 sdd 8:48 [active][ready] mpath0 (360a f68656c6f f) dm-0 NETAPP,LUN [size=5.0g][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=4][active] \_ 0:0:0:0 sda 8:0 [active][ready] \_ 1:0:0:0 sdc 8:32 [active][ready] If you see similar output, you are finished because the multipath setup was performed automatically. No further multipath configuration is necessary. If you do not see similar output, continue to the next step. 3. Create multiple iscsi sessions (multiple paths) a. Enter the command ls -d /sys/block/sd* to see how many block devices are found by the initrd image created by the installer, as follows: # ls -d /sys/block/sd* /sys/block/sda /sys/block/sdb b. Enter the command iscsiadm -m node --login to find other iscsi paths: # iscsiadm -m node --login Logging in to [iface: default, target: iqn com.netapp:sn , portal: ,3260] Logging in to [iface: default, target: iqn com.netapp:sn , portal: ,3260] Login to [iface: default, target: iqn com.netapp:sn , portal: ,3260]: successful iscsiadm: Could not login to [iface: default, target: iqn com.netapp:sn , portal: ,3260]: iscsiadm: initiator reported error (15 - already exists) c. You should see extra device paths in the /sys/block/ directory after running the above command. These devices are newly-created iscsi paths. In this example, the newly-discovered iscsi paths are sdc and sdd, as follows: # ls -d /sys/block/sd* /sys/block/sda /sys/block/sdb /sys/block/sdc /sys/block/sdd 4. Edit the /etc/multipath.conf file. a. Ensure that the file contains the following line: defaults { user_friendly_names yes } b. Multipath-tools blacklist everything listed within the blacklist {} statement contained in the /etc/multipath.conf file. Comment out the wwid line within the blacklist {} statement so that the iscsi devices are not blacklisted. For example, here is a modified multipath.conf file: # cat /etc/multipath.conf defaults { user_friendly_names yes } blacklist { devnode "^(ram raw loop fd md dm- sr scd st)[0-9]*" devnode "^(hd xvd vd)[a-z]*" # wwid "*" } 18 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

27 5. Enter the multipath command to create a bindings file named /var/lib/multipath/bindings. This file is included in the new initrd image. # multipath 6. Edit /etc/fstab file to ensure it doesn't have single path device names or LABELs The /etc/init.d/netfs script may try to mount single path names (such as /dev/sda1) because the label is the same on a single path device as well as its corresponding multipath device name. However, the script cannot mount the device because the corresponding multipath device is already active. To avoid this error during boot, edit the /etc/fstab file and replace any LABELs or path names with LVM names or multipath names, as appropriate. See the next step for an example. In this example, the default LVM partitioning scheme was accepted during system installation so the /etc/fstab file on the test system contains the following LABEL entry: LABEL=/boot / boot ext3 defaults,_netdev 1 2 a. Find out which multipath device corresponds to /boot LABEL. Enter the blkid -l -t LABEL=/boot command to determine which device has /boot LABEL. The following output shows that /dev/sda1 has /boot LABEL: # blkid -t LABEL=/boot /dev/sda1: LABEL="/boot" UUID="cec3f5e afb-a3fec0b40ccb4420" SEC_TYPE="ext2" TYPE="ext3" b. Determine the wwid (World Wide IDentifier, a unique identifier for a logical unit in a SCSI storage subsystem) of the boot device (/dev/sda in this example) by typing the following command: # /sbin/scsi_id -g -u -s /block/sda 360a f68656c6f f c. Determine the boot device's mpath name by looking at the /var/lib/multipath/bindings bindings file. In our bindings file, the wwid of sda corresponds to mpath0: # cat /var/lib/multipath/bindings # Multipath bindings, Version : 1.0 # NOTE: this file is automatically maintained by the multipath program. # You should not need to edit this file in normal circumstances. # # Format: # alias wwid # mpath0 360a f68656c6f f mpath1 360a f68656c6f d. In general, multipath device names take the form of /dev/mapper/mpathxpy, where X is the multipath number and Y is the partition number. From the previous step, mpath0 corresponds to /dev/sda. Therefore, you can translate /dev/sda1 to /dev/mapper/mpath0p1 and replace the LABEL=/boot with the multipath device name of /dev/sda1: /dev/mapper/mpath0p1. Here is the new entry for the boot device in the /etc/fstab file: /dev/mapper/mpath0p1 /boot ext3 defaults,_netdev 1 2 It replaces the old entry: LABEL=/boot /boot ext3 defaults,_netdev 1 2 Note: If you choose to not to use friendly names in step 4.a, you need to use this format: /dev/mapper/<wwid>p<partition number> for the multipath device names. For example, here is an entry in /etc/fstab for /boot without friendly names: /dev/mapper/360a f68656c6f fp1 /boot ext3 defaults,_netdev Create an iscsi/multipath capable initrd image by following these steps: a. Save the original /sbin/mkinitrd and /boot/initrd image files for backup. Enter the following commands to create backup files: # cp /sbin/mkinitrd /sbin/mkinitrd.orig # cp /boot/initrd el5.img /boot/initrd el5.img.orig b. Edit the /sbin/mkinitrd file. Open the file and search for the findstoragedriver () function. The arguments passed to findstoragedriver () are not correct for the default LVM installation. Typing Chapter 5. Installing Linux on a Multipath iscsi LUN on an IP Network 19

28 ls -d /sys/block/sd* shows you all paths. Replace the in the first line of findstoragedriver() function definition with your list of all boot and root device paths. On the test system, there are two disks with two paths per disk, for a total of four path names. Therefore, change the for loop from: for device in $@ ; do to: for device in sda sdb sdc sdd; do c. Enable multipath in the mkinitrd script. Search within the /sbin/mkinitrd file for use_multipath=0, and change it to use_multipath=1. On the test system, this definition is on line d. Because your specific devices are not going to be listed in the initrd image created by the default /sbin/mkinitrd script, you must add them to the correct place in the script. Search for "echo Creating multipath devices" in the file. On the test system, this definition was found on line For each of your multipath disks, add a line such as the following example after the echo command: emit "/bin/multipath -v 0 <wwid>" For example, on the test system, these two lines were added to the /sbin/mkinitrd file: emit "/bin/multipath -v 0 360a f68656c6f f" emit "/bin/multipath -v 0 360a f68656c6f " To show the changes that we made, here is a comparison between the original and the modified mkinitrd file: # diff -Nau /sbin/mkinitrd.orig /sbin/mkinitrd --- /sbin/mkinitrd.orig :29: /sbin/mkinitrd ,7 } findstoragedriver () { - for device in $@ ; do + for device in sda sdb sdc sdd ;do case " $handleddevices " in *" $device "*) continue -1222,7 echo $NONL "$@" >> $RCFILE } -use_multipath=0 +use_multipath=1 use_emc=0 use_xdr=0 if [ -n "$testdm" -a -x /sbin/dmsetup -a -e /dev/mapper/control ]; -1666,6 if [ "$use_multipath" == "1" ]; then emit "echo Creating multipath devices" + emit "/bin/multipath -v 0 360a f68656c6f f" + emit "/bin/multipath -v 0 360a f68656c6f " for wwid in $root_wwids ; do emit "/bin/multipath -v 0 $wwid" done e. Use the modified mkinitrd script to create a new initrd image: # mkinitrd -f /boot/initrd-$(uname -r).img $(uname -r) f. Reboot your system: # reboot 20 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network

29 8. After the system reboots, the root file system image should be discovered on multpath iscsi devices. Repeat the instructions in step 2 to verify. 9. To ensure that these changes persist even if you change the storage environment, follow these steps: a. Restore the original mkinitrd that you saved in step 8.1: # cp /sbin/mkinitrd.orig /sbin/mkinitrd b. Edit /etc/sysconfig/mkinitrd/multipath file and change MULTIPATH=no to MULTIPATH=yes. If this file does not exist on your system, create the file by entering the following command: echo "MULTIPATH=yes" > /etc/sysconfig/mkinitrd/multipath Related reference: Chapter 1, Scope, requirements, and support, on page 1 This blueprint applies to System x running Linux and PowerLinux. You can learn more about the systems to which this information applies. Installing SLES 11 on a multipath iscsi storage device (System x only) The following steps are currently supported in System x only. Procedure 1. Follow all the steps in the iscsi Overview blueprint at lnxinfo/v3r0m0/topic/liaai/iscsi/liaaiiscsi.htm to install SLES 11 on an iscsi LUN. The following steps are needed once you have completed the installation and your system has rebooted. 2. Enable Multipath services at system startup by entering the following commands: # chkconfig boot.multipath on # chkconfig multipathd on 3. Create the /etc/multipath.conf file. The default SLES 11 installation does not create the /etc/multipath.conf file. See the /usr/share/doc/packages/multipath-tools/ directory for more information. In that directory, refer to the multipath.conf.synthetic template and the multipath.conf.annotated HOWTO. In the test environment, the multipath.conf.synthetic file was copied to the /etc/multipath.conf file. To do so, enter the following command: # cp /usr/share/doc/packages/multipath-tools\ /multipath.conf.synthetic /etc/multipath.conf All entries in the example file are commented. You can change the values in this file if necessary for your environment. 4. Enter the iscsiadm -m discovery -t sendtargets -p <target node ip address>:<target port> command to add the node records that were not discovered during installation. In this example, there are two target nodes ( and with the default iscsi target port 3260) # iscsiadm -m discovery -t sendtargets -p : :3260,1001 iqn com.netapp:sn :3260,1000 iqn com.netapp:sn # iscsiadm -m discovery -t sendtargets -p : :3260,1001 iqn com.netapp:sn :3260,1000 iqn com.netapp:sn Enter the iscsiadm -m node -p <target node ip address>:<target port> -T <target IQN> -o update -n node.startup -v onboot command to set each node to start up onboot. Note that the test target IQN is iqn com.netapp:sn # iscsiadm -m node -p :3260 -T iqn com.netapp:sn \ -o update -n node.startup -v onboot # iscsiadm -m node -p :3260 -T iqn com.netapp:sn \ -o update -n node.startup -v onboot 6. Enter the iscsiadm -m node -p <target node ip address>:<target port> -T <target IQN> -o update -n node.conn\[0\].startup -v onboot command to set each node connection to start up onboot Chapter 5. Installing Linux on a Multipath iscsi LUN on an IP Network 21

30 # iscsiadm -m node -p :3260 -T iqn com.netapp:sn o update -n node.conn\[0\].startup -v onboot # iscsiadm -m node -p :3260 -T iqn com.netapp:sn o update -n node.conn\[0\].startup -v onboot 7. Verify that the host system can now find all iscsi paths required for booting a. Enter the ls -d /sys/block/sd* command to see how many block devices are found by the initrd image created by the installer, as follows: # ls -d /sys/block/sd* /sys/block/sda /sys/block/sdb b. Enter the iscsiadm -m node --login command to find other iscsi paths: # iscsiadm -m node --login Logging in to [iface: default, target: iqn com.netapp:sn , portal: ,3260] Logging in to [iface: default, target: iqn com.netapp:sn , portal: ,3260] Login to [iface: default, target: iqn com.netapp:sn , portal: ,3260]: successful iscsiadm: Could not login to [iface: default, target: iqn com.netapp:sn , portal: ,3260]: iscsiadm: initiator reported error (15 - already exists) c. You should see extra device paths in the /sys/block/ directory after running the above command. These devices are newly-created iscsi paths. In this example, the newly-discovered iscsi paths are sdc and sdd, as follows: # ls -d /sys/block/sd* /sys/block/sda /sys/block/sdb /sys/block/sdc /sys/block/sdd 8. Create a multipath-capable initrd image a. Edit the /etc/sysconfig/kernel file to add dm-multipath to INITRD_MODULES keyword. If your storage configuration requires additional multipath modules, add them here as well. On the test system, only dm-multipath was added, as the storage NetApp File server did not need additional kernel modules. Here is a comparison between the original and modified file on the test system: # diff -Nau /etc/sysconfig/kernel.orig /etc/sysconfig/kernel --- /etc/sysconfig/kernel.orig :46: /etc/sysconfig/kernel ,7 # ramdisk by calling the script "mkinitrd" # (like drivers for scsi-controllers, for lvm or reiserfs) # -INITRD_MODULES="processor thermal fan jbd ext3 edd" +INITRD_MODULES="dm-multipath processor thermal fan jbd ext3 edd" ## Type: string ## Command: /sbin/mkinitrd b. Create a backup copy of your initrd file c. Run the mkinitrd command to create an initrd image: # mkinitrd 9. Update your boot loader configuration with the new initrd, if needed. During the test, the original initrd file was overwritten, so the boat loader configuration file did not require updating. 10. Reboot with the new initrd image and verify that your root is on multipath. a. Use the mount command to find where the root is. The following output shows that root is on the device mapper (DM) device /dev/dm-3: # mount /dev/dm-3 on / type ext3 (rw,acl,user_xattr) /proc on /proc type proc (rw) sysfs on /sys type sysfs (rw) debugfs on /sys/kernel/debug type debugfs (rw) udev on /dev type tmpfs (rw) devpts on /dev/pts type devpts (rw,mode=0620,gid=5) fusectl on /sys/fs/fuse/connections type fusectl (rw) securityfs on /sys/kernel/security type securityfs (rw) 22 Blueprints: Installing Linux on a Multipath iscsi LUN on an IP Network