Shared storage disk settings for Category 1 Storage Devices

Recommended settings for Category 1 Storage devices and multipath I/O driver combinations in pureScale environments when enabling the SCSI-3 Persistent Reserve feature.

Enabling SCSI-3 Persistent Reserve feature in the storage device involves a trial attempt to reserve and unreserve target disks in exclusive mode by IBM Reliable Scalable Cluster Technology (RSCT) peer domain and IBM® Storage Scale during Db2® instance setup. If this step succeeds, relevant attributes of the target disks are altered to reflect the SCSI-3 PR enablement. This step can fail if the target disks contain stale reservation bits from previous use. You can set the pre-Db2 instance on the target disks to clear any previously existing reservation or unexpected bits to ensure a smooth instance setup.

Before creating a pureScale instance, it is recommended that the disk RSCT peer domain attribute, RESERVE_POLICY, be set to no_reserve. This recommendation applies to all supported shared storage devices, device drivers, and disk types.

Once db2icrt is finished running and the Db2 pureScale instance is created, some of these attributes are updated by RSCT peer domain and IBM Storage Scale as they try to open the device in the mode specified.
  • For the RSCT peer domain tiebreaker disk, the ALGORITHM value is set to fail_over and TIMEOUT_POLICY value is set to retry_path if the TIMEOUT_POLICY exists
    • If the disk has SCSI-3 PR enabled, then RESERVE_POLICY value is set to PR_exclusive
    • If the disk has SCSI-2 enabled, then RESERVE_POLICY value is set to single_path
  • For the IBM Storage Scale NSDs and the IBM Storage Scale tie breaker disk for when the disk quorum is used, the recommended value for ALGORITHM is fail_over or load_balance and for TIMEOUT_POLICY is retry_path
    • If the disk has SCSI-3 PR enabled, the RESERVE_POLICY value is set to PR_shared
    • If the disk does not have SCSI-3 PR enabled, the RESERVE_POLICY value is set to no_reserve, if the RESERVE_POLICY exists
Note:
  1. All values that are mentioned for ALGORITHM, RESERVE_POLICY, and TIMEOUT_POLICY are validated by IBM. Other values might not produce the behavior that is expected by Db2 pureScale®.
  2. For the SDDPCM device driver, if ALGORITHM is set to fail_over, the TIMEOUT_POLICY attribute must be set to retry_path. For more information, the support page for Subsystem Device Driver Path Control Module (SDDPCM).