Ramdisk (Memory-based Disk) Support on HP-UX 11i v2

Transcription

1 Ramdisk (Memory-based Disk) Support on HP-UX 11i v2 Introduction... 2 Terms and Definitions... 2 Ramdisk Features in HP-UX 11i v Ramdisk Installation... 3 Ramdisk Configuration... 3 Ramdisk Device Special File (DSF)... 3 No-swap and Swap Ramdisks... 4 Ramdisk Performance... 4 Ramdisk Support... 4 LVM Support... 4 File System Support... 4 I/O Statistics Support... 4 Ioscan Support... 5 Diskinfo Support... 5 SAM Support... 5 Ramdisk vs Memfs... 6 Limitations... 6 Related Information

2 2 Introduction Ramdisk is an emulation of a disk in memory (RAM) which operates at high speeds. HP-UX 11i v2 supports creating a ramdisk in no-swap or swap memory. A no-swap memory-based ramdisk operates on memory pages that are always resident in system memory, so the ramdisk can operate at guaranteed close-to-memory speeds. A swap memory-based ramdisk operates on memory pages that may be paged out based on system memory pressure, so the ramdisk performance can vary depending on system memory pressure. Typical usages of a ramdisk are in large database applications, file system servers, FTP servers, and so forth. A database application that uses huge temporary files can configure those files on a ramdisk. An ftp server can mount the ftp directories on a ramdisk for better performance. File system servers can have shared file systems residing on a ramdisk. Certain applications have confidential data files that are active for a certain period of time then must be completely destroyed to protect privacy. Frequent removal of data files in such cases can be done efficiently on a ramdisk. Ramdisk keeps its contents in memory, and its contents are volatile. Ramdisk contents are not persistent across reboots. Terms and Definitions LVM DSF SAM Logical Volume Manager Device Special File System Administration Manager Ramdisk Features in HP-UX 11i v2 In HP-UX 11i v2, ramdisk supports the following features: Creation of ramdisks using no-swap memory, up to a maximum 4GB per ramdisk. Creation of large ramdisks using swappable memory, up to 256GB per ramdisk (tested limit). ramutil(1m) tool to manage ramdisks. ioscan(1m), SAM, Glance, and diskinfo(1m) support. LVM and VxFS support (See details in LVM, File system sections ). Persistent ramdisk configuration across reboots. Note that data on a ramdisk is not preserved across reboots. Up to 14 instances of ramdisk at a time system-wide.

3 3 Ramdisk Installation The ramdisk support in HP-UX 11i v2 is delivered in two core patches one command and one kernel patch. PHKL_37170 delivers necessary support for ramdisk in the kernel. This patch also delivers the ramdisc(7) man page. PHCO_37169 delivers the ramutil tool with an associated ramutil(1m) man page, and scripts to manage ramdisks. Ramdisk command/kernel patches are dependant on each other, and have to be installed together. In addition, kernel patch PHKL_36321 and LVM patch PHCO_34421 are required for ramdisk functionality. To configure ramdisk using SAM, install SAM patch PHCO_ Without this patch, ramdisks are not visible in SAM. Ramdisk Configuration The ramutil command creates and removes ramdisks. Each ramdisk in the system is identified by a unique volume/instance number. Ramdisk supports 14 ramdisks with instance numbers ranging from A ramdisk instance uses either swap memory or no-swap memory, depending on the ramutil options you specify at creation. Swap and no-swap ramdisks can not co-exist at the same volume/instance number. Ramdisk Device Special File (DSF) For every ramdisk in the system, two DSFs are created as below: For example: /dev/dsk/ram[volume number] this represents the block DSF. /dev/rdsk/ram[volume number] this represents the raw DSF. brw-r bin sys 9 0x May 21 12:26 /dev/dsk/ram1 crw-r bin sys 9 0x May 21 12:26 /dev/rdsk/ram1 The ramutil command provides option to re-create any missing DSFs for all active ramdisk instances in the system. For more information, see the ramutil(1m) manpage. Ramdisk configurations in the system remain persistent across reboots. Ramdisk contents, however, including any file systems, are lost across a reboot. Ramdisk configurations in the system are tracked in the file /etc/ramdsktab. This file is managed by ramdisk utilities, and must not be manually edited. RC scripts /sbin/rc2.d/s295ramdisk and /sbin/rc1.d/k705ramdisk handle ramdisk configurations across system reboot and shutdown. When creating a ramdisk, you can specify its size in kilobytes (KB) or in gigabytes (GB) for large ramdisks. If you specify KB, ramutil rounds down the size of ramdisk to the next 64KB boundary. If you specify GB, ramutil rounds down the size of ramdisk to the next 1GB boundary.

4 4 No-swap and Swap Ramdisks A no-swap ramdisk uses memory pages that always stay resident. I/O operations to a no-swap ramdisk can operate at close to memory speeds. A no-swap ramdisk reserves system physical memory equal to its size during its existence. The size of a no-swap ramdisk can not exceed 4GB. Depending upon system configurations and limitations, the maximum supported size of no-swap ramdisk can vary. A swap ramdisk uses memory pages that can get paged depending on system memory pressure. A swap ramdisk does not reserve system physical memory; it operates on memory pages that in turn use physical memory based on demand. On systems with adequate physical memory and swap space, swap ramdisks of large sizes can be created. Swap ramdisks of 256GB size have been. When creating swap ramdisks, consider the following: If you are creating swap ramdisks larger than 4GB, you must increase the maxdsiz_64bit tunable appropriately. For details, see the maxdsiz_64bit(5m) and kctune(1m) man pages. The sum of available physical memory and swap space in the system defines the maximum possible memory size available for creating swap ramdisks. If swap space is inadequate, you must configure additional swap space. For details, see swapon(2m) and fstab(4m). Ramdisk Performance Read and write operations to a no-swap ramdisk can complete at near memory speeds, since the ramdisk is configured on memory pages that are always resident. The performance of a swap ramdisk depends on system memory pressure. If paging activity in the system is negligible, and the ramdisk pages stay resident in memory, a swap ramdisk can achieve speeds close to that of no-swap ramdisk. Ramdisk Support LVM Support Ramdisks can be configured in LVM just like a physical disk. However, ramdisks are not supported as spare disks or in mirrored LVM configurations. See Limitations. If a ramdisk remains configured in LVM across a system reboot, the LVM subsystem displays messages regarding a missing ramdisk. This is because the ramdisk contents are lost across reboot. File System Support Both VxFS and HFS are supported on ramdisks. However, since ramdisk data is not persistent across reboots, ramdisk entries in the /etc/fstab file are not supported. I/O Statistics Support Use glance(1m) to collect ramdisk I/O statistics.

5 5 Ioscan Support Ramdisks are visible in the I/O configuration under the I/O Tree virtual root, /255. Sample ioscan output: # ioscan -fknh /255 Class I H/W Path Driver S/W State H/W Type Description ============================================================== vroot_rdsk 0 255/43 rdsk_root CLAIMED VIRTBUS disk /43/12 ramdisc CLAIMED DEVICE HP Ramdisk (NoSwap) 1.0 /dev/dsk/ram12 /dev/rdsk/ram12 disk /43/13 ramdisc CLAIMED DEVICE HP Ramdisk 1.0 /dev/dsk/ram13 /dev/rdsk/ram13 In the sample output, /255 refers to the I/O Tree virtual root. Below this, the ramdisk virtual root vroot_rdsk is configured at hardware path /255/43. Ramdisks are registered below the path /255/43. In the output, the description HP Ramdisk (NoSwap) refers to a ramdisk that uses noswap memory. HP Ramdisk refers to a ramdisk that uses swap memory. If a ramdisk instance is removed, its state becomes NO_HW, as in following ioscan output: # ioscan -fnh /255 Class I H/W Path Driver S/W State H/W Type Description ========================================================================= vroot_rdsk 0 255/43 rdsk_root CLAIMED VIRTBUS disk /43/12 ramdisc NO_HW DEVICE HP Ramdisk (NoSwap) disk /43/13 ramdisc NO_HW DEVICE HP Ramdisk Diskinfo Support The diskinfo command supports ramdisks. For example: # diskinfo /dev/rdsk/ram12 SCSI describe of /dev/rdsk/ram12: vendor: HP product id: RAM_DISK type: direct access size: Kbytes bytes per sector: 1024 SAM Support Ramdisks can be configured using SAM. SAM patch PHCO_37169 must be installed to configure ramdisk using SAM.

6 6 Ramdisk vs Memfs The memfs file system provides an optimized memory-based file system solution. Ramdisk does not provide any file system; it only emulates a disk in memory. However, you can create a file system to operate on a ramdisk. Ramdisk also supports raw access to the disk. Since ramdisk emulates a disk, it can be extended to support different file systems and volume managers. Currently VxFS, HFS, and LVM are supported. Limitations LVM mirror configurations are not supported with ramdisk. WARNING: HP-UX 11i v2 (11.23) Ramdisk version 1 has not been certified for use with HP's Logical Volume Manager (LVM) in mirrored configurations. HP does not support such configurations since there is a possibility of data loss from a redundancy failure of a physical disk or disk interface component. Other LVM mirrored configuration failure modes may exist that may further impact data integrity. Note: Ramdisk data is not persistent across system reboots. HP disclaims all warranties, express or implied, including but not limited to the implied warranties of merchantability, fitness for a particular purpose, and noninfringement, if you use HP-UX 11i v2 (11.23) Ramdisk version 1 with LVM mirrored configurations, you assume all responsibility for any problems resulting from such usage in these configurations. Third party products exist that provide ramdisk based LVM mirrored configurations with additional support software; these products are delivered on configurations tested and validated by the product vendor. The use of such products is permitted on 11i v2 (11.23); the third party product vendors are responsible for supporting these products. Ramdisks can not be used as spare disks in LVM mirror configurations. Ramdisk is not tested or certified with VxVM, vpars, or HP VM environments. Ramdisk is not supported for use in any root/boot/swap/dump configurations. Ramdisk can not be part of LVM devices used for configuring root/boot/swap/dump. Related Information For more information, see the HP-UX 11i v2 Ramdisk Release Notes at Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein. UNIX is a registered trademark of The Open Group.