Protection from the case where precisely half the hosts fail is of particular importance in a two machine configuration with an even number of hosts. In this configuration, where a single machine failure causes half the hosts to fail, a tiebreaker is needed to obtain operational quorum.
DB2 pureScale Feature supports all storage area network (SAN) and directly attached shared block storage, referenced as a logical unit number (LUN).
Before recovering a failed member in the DB2 pureScale instance, DB2 cluster services ensures that it is not possible for the failed member to modify shared data on disk. This precaution is known as I/O fencing. Some storage controllers and multipath I/O driver combinations support specialized capability, known as SCSI-3 Persistent Reserve (PR), with the write exclusive all registrants persistent reservation type (type 7h). This type enables DB2 cluster services to perform fast I/O fencing, in as little as 1 - 2 seconds.
Recovery time is the elapsed time from a host failure until the release of locks for uncommitted transactions. For a typical OLTP workload with short transactions, fast I/O fencing results in recovery times of approximately 20 seconds. Fast I/O fencing is much faster than the alternative method, based on expiry of lock leases. When deciding which category to use, evaluate if fast I/O fencing support is required to meet your service level agreements (SLAs).
A subcluster of hosts requires operational quorum for IBM Reliable Scalable Cluster Technology (RSCT) to allow the subcluster to continue running the DB2 pureScale instance in the event of host failures. To be granted operational quorum by RSCT, a subcluster must contain a majority of the hosts. If exactly half of the hosts in cluster remain in communication, the tiebreaker can be exclusively reserved by that subcluster to obtain operational quorum.
In DB2 Cancun Release 10.5.0.4 and later fix packs, on supported AIX® and Linux operating systems, the device used as the cluster manager tiebreaker disk must have SCSI-3 PR WRITE EXCLUSIVE REGISTRANTS ONLY reservation type code 0x50 enabled.
The tiebreaker disk is not a requirement. However, if your cluster has an even number of machines and you do not have a tiebreaker disk, if half of the machines in the cluster fail, operational quorum is lost. You must have operational quorum for the cluster to be up and running. Without operational quorum, the database is not available for use.
Upgrading SDDPCM to 2.6.3.x might cause device configurations to fail if the algorithm attribute on the upgraded device is set to fail_over. If the device configuration settings fail, the DB2 pureScale cluster might be affected. You must set the timeout_policy attribute to retry_path if you want to use the fail_over option on the algorithm attribute. For more information, see http://www-01.ibm.com/support/docview.wss?&uid=ssg1S1004072.
Storage Devices | Multipath I/O drivers required for AIX systems | Multipath I/O drivers required for Linux systems | Protocol |
---|---|---|---|
IBM Storwize® V7000 (6.4.0.1 or higher) | SDDPCM, MPIO | DM-MP | Fibre Channel |
IBM SAN Volume Controller (6.4.0.1 or higher) | SDDPCM, MPIO | DM-MP | Fibre Channel |
IBM System Storage® DS8000® series | SDDPCM driver provided by IBM (driver file devices.fcp.disk.ibm.mpio.rte and devices.sddpcm<Your specific AIX version>.rte) | DM-MP | Fibre Channel |
IBM System Storage DS5000 series | MPIO driver provided by IBM (driver file devices.fcp.disk.ibm.mpio.rte) | DM-MP or RDAC | Fibre Channel |
IBM System Storage DS4000® series | MPIO driver provided by IBM (driver file devices.fcp.disk.ibm.mpio.rte) | DM-MP or RDAC | Fibre Channel |
IBM System Storage DS3000 series | MPIO driver provided by IBM (driver file devices.fcp.disk.ibm.mpio.rte) | DM-MP or RDAC | Fibre Channel |
EMC VMAX/Symmetrix family 1 | EMC PowerPath 5.5 P04 B00310 and EMC AIX ODM Package 5.3.0.6 MPIO driver provided by EMC (driver file EMC.Symmetrix.fcp.MPIO.rte) |
DM-MP | Fibre Channel |
NetApp FAS filers | MPIO driver provided by NetApp | DM-MP | iSCSI |
Virtual I/O Server (VIOS) 2 | MPIO or SDDPCM | Not Applicable | Fibre Channel |
Hitachi Virtual Storage Platform (VSP)5 | MPIO driver provided by IBM or HDLM | not supported as category 1 in Linux | Fibre Channel |
Hitachi Universal Storage (HUS) 100 Series6 | MPIO driver provided by IBM or HDLM | DM-MP | Fibre Channel |
Hitachi Universal Storage (HUS) VM7 | MPIO driver provided by IBM or HDLM | not supported as category 1 in Linux | Fibre Channel |
Hitachi VSP G10007 | MPIO driver provided by IBM or HDLM | not supported as category 1 in Linux | Fibre Channel |
IBM XIV® Storage System | MPIO | DM-MP8 | Fibre channel |
IBM FlashSystem™ 8409 | MPIO driver provided by IBM (driver file devices.fcp.disk.ibm.mpio.rte) | DMMP | Fibre Channel |
IBM Storwize V5000 (7.3.0 or higher)9 | SDDPCM | DM-MP | Fibre Channel |
Note:
|
Storage Devices | Multipath I/O drivers required for AIX systems | Multipath I/O drivers required for Linux systems | Protocol |
---|---|---|---|
EMC VMAX/Symmetrix family | EMC PowerPath | Fibre Channel | |
Hitachi Universal Storage Platform V (USP V) | MPIO | Fibre Channel |
All storage devices and multipath I/O driver combinations not identified as category 1 or category 2 fall into category 3. Category 3 combinations have not been validated with the DB2 pureScale Feature, though they are supported.