DB2 10.5 for Linux, UNIX, and Windows

Shared storage support for DB2 pureScale environments

Shared storage devices supported by IBM® DB2® pureScale® Feature are divided into three categories. These categories group storage devices and multipath I/O driver pairs based on two storage features. The two features, fast I/O fencing support, and DB2 cluster services tiebreaker support, provide faster recovery times for failed hosts, better resiliency and improve availability.

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).

Fast I/O fencing

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).

DB2 cluster services tiebreaker support

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.

Subsystem Device Driver Path Control Module (SDDPCM)

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.

Category 1 storage device and multipath I/O driver combinations

Storage devices and multipath I/O driver combinations listed in this category can successfully support both the DB2 cluster services tiebreaker and fast I/O fencing. Category 1 devices have been validated with the DB2 pureScale Feature and result in the highest resiliency and fastest recovery times.

Table 1. Category 1 storage device and multipath I/O driver combinations
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: Each host port connected to the EMC VMAX/Symmetrix family storage system must have the SCSI_3 (SC3) flag set on the front-end adapter port configuration. On the hypervolume, the logical unit number (LUN), used for the DB2 cluster services tiebreaker the SCSI3_persist_reserv option must be set. On supported Linux systems, the device selected for cluster manager (RSCT) tiebreaker, must support reservation type of WRITE EXCLUSIVE REGISTRANTS ONLY type code 5h. With SCSI-3 PR, there is one persistent reservation holder, which is the node that acquires the quorum device. A DB2 pureScale cluster using EMC VMAX shared storage, must have the SCSI3_persist_reserve type option enabled for the disks mapped. It is not enabled by default. A Virtual I/O Server must be used with N_Port ID Virtualization (NPIV) for a storage system and an AIX system multipath I/O driver combination. The VIOS storage is in the same category of storage that the underlying physical hardware storage system is in. For VIOS storage to be considered category 1 storage the physical storage hardware and driver combination must be in the category 1 table. Starting from SDDPCM v2630 and higher, before installing the DB2 pureScale Feature, you must change the timeout_policy attribute to retry_path on the tiebreaker disk. To change the value of the timeout_policy attribute, enter the following command: `chdev -l hdiskX -a timeout_policy=retry_path` For details, see: http://www-01.ibm.com/support/docview.wss?rs=540&context=ST52G7&dc=D600&uid=ssg1S1004072&loc=en_US&cs=utf-8&lang=en For more information about these drivers, see: For RDAC: http://www.lsi.com/sep/Pages/rdac/index.aspx For DM-MP on RHEL 6.1: http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/DM_Multipath/index.html For DM-MP on SUSE: http://www.novell.com/documentation/sles11/stor_admin/?page=/documentation/sles11/stor_admin/data/bookinfo.html The following restrictions apply: HDLM (Hitachi Dynamic Link Manager) for AIX Version 7.3.1 or later provided by Hitachi Minimum micro code level 70-04-31-00/00 If HDLM is used, set the load balancing setting of the tiebreaker disk to OFF using HGLM (Hitachi Global Link Manager Software) Fast I/O fencing (SCSI-3PR) enabled Specific settings for disks that have fast I/O fencing enabled and are part of the GPFS™ file system: On AIX, host mode options 72 on Fibre channel only when HDLM is used The following restrictions apply: HDLM for AIX Version 7.3.1 or later provided by Hitachi Multipath I/O drivers required for Linux systems - DM- MP only Minimum micro code level 0945/A Select the Allocation length Expand mode check box if the disk is to be used as a tie breaker disk Fast I/O fencing (SCSI-3PR) enabled Select the Unique Reserve mode 2 check box for disks that are part of the GPFS file system and have fast I/O fencing enabled The following restrictions apply: Supported only on AIX platforms HDLM for AIX Version 7.3.1 or later provided by Hitachi HUS VM minimum micro code level 73-01-32-00/00 VSP G1000 minimum micro code level 80-01-41-00/00 If HDLM is used, set the load balancing setting of the tiebreaker disk to OFF using HGLM Fast I/O fencing (SCSI-3PR) enabled Specific settings for disks that have fast I/O fencing enabled and are part of the GPFS file system: Host mode options 72 on Fibre channel only when HDLM is used On Linux operating systems, SCSI-3 PR is not enabled automatically with IBM XIV Storage. You must manually enable SCSI-3 PR. For details see Enabling SCSI-3 Persistent Reserve for DB2 pureScale Feature Supported in DB2 Cancun Release 10.5.0.4 and later fix packs. To support SCSI-3 PR changes in EMC PowerPath 5.5 P04 B003, EMC Symmetrix must be running Enginunity code 5876 base-level or higher.

Category 2 storage device and multipath I/O driver combinations

Storage devices and multipath I/O driver combinations listed in this category are supported and have been validated with the DB2 pureScale Feature. The combinations in this category can successfully support the DB2 cluster services tiebreaker, but not fast I/O fencing.

Table 2. Category 2 storage device and multipath I/O driver combinations
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

Category 3 storage device and multipath I/O driver combinations

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.

Recovery times for host failures in a DB2 pureScale environment are competitive with other vendors solutions, regardless of the category of storage device and multipath I/O driver.

Note: Storage devices in this category might not have the capability to support fast I/O fencing or the disk tiebreaker capabilities.