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Using the PSP_RR path selection policy with MSCS results in quorum disk problems (1010041)

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Symptoms

When you use the PSP_RR path selection policy with MSCS, the quorum disk experiences problems and the cluster may not operate.

Purpose

MSCS conducts SCSI-3 reservations on the quorum disk. SCSI-3 registration sent down one path allows the MSCS cluster to do SCSI-3 reservations only on that path. When PSP_RR later switches to another path, MSCS receives an error if it tries to do a reservation or use other SCSI-3 commands, depending on the reservation.

Resolution

This issue is resolved in vSphere 5.5. For more information about this version, see the VMware vSphere 5.5 Release Notes. You can download the latest release from the VMware Download Center.

With the introduction of round-robin support, there are a number of changes for the SCSI locking mechanism used by MSCS when a failover of services occurs. To facilitate this new path policy, these changes mean that it is irrelevant which path is used to place the SCSI reservation; any path can free the reservation.

For ESX versions 5.1 and earlier, do not switch the device used for the MSCS quorum disk to PSP_RR. Instead, use the PSP_MRU or PSP_FIXED policies depending on the normal default for the array.
 
ESXi uses Roundrobin policy (VMW_PSP_RR) for some storage arrays by default. If you use the LUN for MSCS it must be changed to use a different policy, as specified in this table:

Array SATP PSP to use for MSCS
EMC Clariion ALUA_CX FIXED
EMC Symmetrix SYMM FIXED
EMC VNX ALUA_CX FIXED
HITACHI DEFAULT_AA FIXED
IBM 2810XIV ALUA MRU
IBM 2810XIV DEFAULT_AA FIXED
NETAPP Data ONTAP 7-Mode DEFAULT_AA FIXED

Update History

09/30/2013 - Added resolution information for vSphere 5.5.

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