Live Virtual Class on Linux and z/vm

Transcription

1 Live Virtual Class on Linux and z/vm High Availability Applications Using Disk Mirroring Dr. Holger Smolinski, IBM STG - LTC Boeblingen

2 Agenda Disk mirroring technology State of the art and its snags The enhancements Real-time enhancement Distribution integration Recovery hardening How can I get this to my IT-shop? 2

3 A Typical Storage Environment Setup HBA SAN Critical Data application is mirrored across two storage controllers HBA Storage Contr. HBA Application SW RAID 1, or PPRC like Copy Service HBA Runtime environment Protection against data loss in case of disastrous failure HBA HBA Storage Contr. SAN 3

4 Demo: An Application writes data to a disk... 4

5 What has happened? The Disk device has stopped responding SCSI timeouts do not apply due to queue-if-no-path behavior The Application has encountered an I/O timeout Application Transactions will terminate Rollback attempts may create additional I/O workload Paging and Swapping will stop System tools will not execute due to missing text segments The system will be unresponsive Operator attempts a reboot, which will hang 5

6 Why is disk storage critical? System Utilities File System Host system Application Binaries Runtime environment Page Cache Mem. Mgmt Kernel Disk Storage usage application data but used at runtime Swap space user heap and stack data program text loaded on demand shared memory segments paged out on memory shortage. File System Swap Space Appl. Data 6

7 The solution is simple: Mirror any data across two independent Storage Controllers Secures data against disastrous failure Abandon I/O, if one half is not responsive after timeout But: do not allow both halves to timeout Allow root/swap to be mirrored But: allow boot, when only one half is operational Resynchronize partially after transient failure is over Log desynchronized regions 7

8 Good path: Write Application / System mirror log 8

9 Good path: Write Application / System mirror Log log 9

10 Good path: Write Application / System mirror log 10

11 What's the cost of this on good path? twice the bandwidth as compared to non-mirrored configuration Same as 'normal' SW-RAID1 PPRC requires addt'l bandwidth between storage controllers Twice the cache memory used during I/O Transient: memory is released when I/O is finished Slightly more CPU cycles For duplicating data 11

12 Degraded path: Write Application / System mirror log 12

13 Degraded path: Write Application / System mirror Log 13

14 Degraded path: Write Application / System mirror Log 14

15 Degraded state operations Subsequent write attempts are not mirrored Data will not be duplicated in cache Read requests are not issued against degraded device No additional timeouts will occur Failure of the still active half will cause an I/O stall 15

16 Degraded state demo 16

17 Degraded path: Recovery Application / System mirror Log 17

18 Degraded path: Recovery Application / System mirror Log 18

19 Recovery Process Demo 19

20 Cost of recovery process Additional I/O workload for the system during synchronization Additional I/O bandwidth for read/write of data Additional memory for store-and-forward of data Limited requirement, because regions are synched 1-by-1 CPU load slightly increased Needs to be considered during sizing Utilize I/O bandwidth by no more than 50% of capacity Plan extra memory: region-size * nr of mirrored LVs 20

21 State diagram & Master device Other device(s) Regions Up-to-date Not up-to-date Device Active Degraded Inactive Active Degraded Inactive Up-to-date Active None swap master swap master swap master swap master swap master Degraded Auto recover I/O stall swap master swap master swap master swap master Inactive Online need repair I/O stall need repair Permanent Failure Not up-todate Active Auto recover I/O stall Degraded Auto recover I/O stall Inactive Online need repair I/O stall need repair 21

22 Key differentiators against other SW RAID 1 implementations Non-blocking Previous solutions stall the mirror, if one half is not responding LVM tools previously stalled, if device does not respond Can be achieved by failfast or fail-if-no-path policy at the cost of reduced qualities of service. Timeout handling User specified I/O timeout compatible with DASD behaviour, or queue-if-no-path option of multipath Selective recovery For transient failure, no full synchronisation of mirror contents is required Also available with md-raid1 in SLES10 SP1 mdadm --create <mddev> --name=<name> -e 1.2 -l 1 -n 2 -- bitmap=internal <devs> 22

23 Distribution integration Add-on Package with mirroring module Loads into kernel provided by distribution partner Replacement packages for LVM2 device-mapper mkinitrd Initscripts Additional package for syslog analysis and statistics 23

24 Hardening the solution Perform selective recovery of modified regions Also mirror the log in preparation of partial availability perform log recovery based on timestamps and sequence numbers Allow replacement of defective devices Full synchronization required Synchronization while online using recovery process Adapt IPL/boot process Allow to IPL with partial configuration 24

25 How can I get this to my IT shop? The IBM LVM Disk Mirroring Offering Asset Description STG Lab Services can be contracted (or subcontracted by GTS or a Business Partner) to install, configure and architect this solution at individual clients. Purchase of this asset includes 1 full year of defect support and basic setup/use documentation. Implementation and configuration may also be contracted as a valueadded service scoped and priced to each specific client. Pricing First year, US$40,000 which includes 1 year of DEFECT support Subsequent years, for DEFECT support = US$20,000 Note, all pricing is based on specific contract terms. 24/7 support etc will effect the asset cost. Contact Michael Daubman: mdaubma@us.ibm.com 25

26 Questions? During this LVC Raise hand and speak Use Text Chat and send message to all presenters After the LVC Send to We will collect questions and reply 26

27 Backup 27

28 Comparison vs. HW/SW RAID1 HBA Solution Sychronous Consistency Failover Failback PPRC/ Metro Mirror Yes / Block Always 3 rd Party SW 3 rd Party SW Async PPRC/ Global Mirror Linux/ md RAID1 Linux/ dm-mirror No / continue 5 sec / Loss 3 rd Party SW 3 rd Party SW Yes / Block Always No No Yes / Block Always No No Storage Contr. Metro /Global Mirror SAN SAN SW RAID Syst. Appl. Swap Linux/ dm-rtmirror Timeout / continue No / Recover Auto Auto Storage Contr. HBA 28

29 IBM System z Expo featuring z/os, z/vm, z/vse and Linux on System z October 13-17, 2008 Las Vegas, Nevada For more information please visit: The future runs on System z and your future begins today. Attend the System z Expo to hone your System z skills and learn how the new IBM System z10 Enterprise Class, green by design, provides significantly lower total cost of ownership, reduced energy consumption, improved security and more. More than 300 sessions cover a range of technology topics and the advances related to System z, z/os, z/vm, z/vse, and Linux on System z. Technical experts from IBM System z development, the community of ISV providers, and customers share their experience and expertise for an unforgettable week.