EMC VNX and CX issues with ALUA failover mode 4
It seems that there is an issue with EMC VNX and CX with VMware 4.x when ALUA (failover mode 4) is used.
If there are no data LUNs numbered 0 presented to the VMware, the hosts failover mode 4 can switch back to failover mode 1.
Refer to primus case, emc262738
Symptom After a storage processor reboot (either because of a non-disruptive upgrade [NDU] or other reboot event), the failover mode for the ESX 4.x hosts changed from 4 (ALUA) to 1 on all host initiators.
Cause On this particular array, for each Storage Group a Host LUN Zero was not configured. This allowed the array to present to the host a “LUNZ.” All host initiators had been configured to failover mode 4 (ALUA). When the storage processor rebooted due to a non-disruptive upgrade (NDU), when the connection was reestablished, the ESX host saw the LUNZ as an active/passive device and sent a command to the array to set the failover mode to 1. This changed all the failover mode settings for all the LUNs in the Storage Group and since the Failover Policy on the host was set to FIXED, when one SP was rebooting, it lost access to the LUNs.
Fix VMware will fix this issue in an upcoming patch for ESX 4.0 and 4.1. ESX 5.x does not have this issue.
To work around this issue, you can bind a small LUN, add to the Storage Group and configure the LUN as Host LUN 0 (zero). You will need to reboot each host after adding the HLU 0. For each Storage Group you will need a HLU 0. See solution emc57314 for information on changing the HLU.
These are the directions from VMware for the workaround:
Present a 1.5 GB or larger LUN0 to all ESX hosts. (This volume does not need to be formatted, but must be equal to or larger than 1.5 GB.
Roll a reboot through all hosts to guarantee that they are seeing the LUN 0 instead of the LUNZ. A rescan may work, but a reboot guarantees that they will not have any legacy data for the CommPath volume.
Thanks to Glen for pointing out the reason and solution.
There is a fix in ESX version 5, so those hosts aren’t affected.