Question regarding SCSI-3 Persistent Reservation

Hello Sreeja,

As far as I know, requirement of this bit is totally dependent on OS the LUN is presented to.

From a windows perspective, It's a requirement for Windows 2008 clusters for SC3 or PER bit to be enabled. This volume attribute may be referred to as the PER bit or flag (for SCSI Persistent) or PGR bit or flag (for Persistent Group Reservation).

This flag should be set in certain SC 3.0 environments that require SCSI-3 Persistent Reservation support. Note that this requirement depends on the cluster configuration

Can the PER bit be set for every device in the configuration?

• There is a small risk involved in configuring devices for PER that do not need to be configured as such.
• The Symmetrix stores the persistent reservation information of the devices that are configured for this support. If we get an I/O to one of these devices, we must first check that access privilege of the host that generated the I/O against this information. If, for some reason, we were unable to retrieve this information (media error on the drive on these tracks, etc), we have no choice but to fail the host I/O.
• It is not recommended to set PER on all devices, but at the same time, if you have an environment in which the set of devices requiring PER to be enabled is dynamic and you are aware of this information, you may want to do risk assessment.
• Caution!! Be careful if enabling the PER bit on the VCMDB or V-Max ACLX volume. As per solution emc59914 the PER bit must be enabled on the VCMDB in a Sun Cluster 3.x environment. As per solution emc212577 the PER bit must NOT be enabled on the VCMDB in a Windows 2003 cluster environment.

also, please refer to specific Host connectivity guides (available on Powerlink) on whether this bit is a requirement for specific OS environment or not.

Hi Sreeja,

In Server 2003 clustering, persistent table (that decides which host should have access to the disk) is maintained on the host itself but in Server 2008 Failover clustering, this table is maintained on the Storage. Enabling PER (SCSI3) bit on devices updates the PR table on storage so server 2008 failover clustering can use it.

regards,

Saurabh

Note that in code 5875, (not sure which revision), THE DEFAULT VALUE OF THIS CHANGED WITHOUT ANY NOTICE.

I shouted there because it caused a couple outages in our ESX environment. (ESX 4.1i)  The defualt value used to be scsi3_persist_reserv=no.  Now the default is yes, which can apprently cause problems when presenting storge to ESX clusters.  Worse yet, in the version of SMC that we have (7.3.1.4), you can specifically set the value to nowhen you create the device, but the VMax ignores that, and creates it with a value of yes.

You have to go back and change the devices later in a separate operation.