Db2 pureScale Best Practice Series: 1-Disk Storage Type

Answer

DB2 pureScale supports all SAN storage, with 3 categories of support
• Category 1: Validated storage which supports fast I/O fencing
• Category 2: Validated storage without fast I/O fencing
• Category 3: All other types of shared storage

For production, use Category 1 storage for optimal member recovery time.
• Uses fast IO fencing , known as SCSI-3 Persistent Reserve to quickly isolate shared storage from a failing member , in testing, SCSI-3 PR reduces the time taken to recover from major failures from almost two minutes down to roughly 20-30 seconds in most scenarios.
• Without fast IO fencing, it generally takes several 1-2mins
• SCSI-3 Persistent Reserve should have the write exclusive all registrants persistent reservation type (type 7h)
• Search for “Shared storage support for DB2 pureScale environments” in IBM Knowledge Center for the latest support

If your storage falls into the category 1 list, then it supports fast I/O fencing .
Or you may use following way to check whether it supports SCSI-3 Persistent Reserve

lsattr command could check the SCSI-3 PR status , if the output includes no_reserve, single_path,PR_exclusive and PR_shared , this means disk support SCSI-3 and SCSI 2 ;
If the output prints only "no_reserve, single_path , that indicates disk support only SCSI 2;
lsattr -R -l hdisk2 -a reserve_policy
no_reserve
single_path
PR_exclusive
PR_shared

How to know whether SCSI-3 PR(fast I/O fencing) enabled in the pureScale ?

./mmlsconfig
Configuration data for cluster db2cluster_20150922152243.P3L2:
--------------------------------------------------------------
clusterName db2cluster_20150922152243.P3L2
clusterId 6106356779434752147
dmapiFileHandleSize 32
maxFilesToCache 10000
pagepool 1G
verifyGpfsReady yes
worker1Threads 512
sharedMemLimit 2047M
usePersistentReserve yes
tiebreakerDisks gpfs1nsd
afmHashVersion 1
minReleaseLevel 4.1.1.4
autoload yes
........
usePersistentReserve =yes means we are enjoying the benefit of fast I/O fencing .

./mmlsnsd -X
Disk name NSD volume ID Device Devtype Node name Remarks
---------------------------------------------------------------------------------------------------
gpfs1nsd 097B64DE5601B8AA /dev/hdisk1 hdisk P3L3 pr=yes

The "Remarks" field value pr=yes indicates that SCSI-3 Persistent Reserve has been enabled for the devices found .

How to enable PR ? please redirect knowledge center for detailed procedure .
https://www.ibm.com/support/knowledgecenter/en/SSEPGG_10.5.0/com.ibm.db2.luw.qb.server.doc/doc/t0058724.html