SC Storage Customer Notification: VMware vSphere multipathing changes for ALUA in Storage Center OS version 6.6 and later

This alert pertains to VMware vSphere (ESXi) hosts default multipathing settings and how the addition of ALUA capabilities added in Storage Center OS version 6.6 and later requires host configuration changes to remain within best practices.

Alert:

When upgrading the Storage Center OS to version 6.6 or later, ESXi hosts will detect the Storage Center volumes as being ALUA capable, and automatically switch the Storage Array Type Plug-in (SATP) from VMW_SATP_DEFAULT_AA to VMW_SATP_ALUA for each of the volumes. When this change occurs, any hosts that previously had the Path Selection Policy (PSP) default set to VMW_PSP_RR (Round Robin) or VMW_PSP_FIXED (Fixed), will automatically change to VMW_PSP_MRU (Most Recently Used), which is the default PSP for the VMW_SATP_ALUA module.  Since the MRU PSP is not HCL certified with the Storage Center array, this configuration falls outside of best practices.  The MRU PSP may have the undesired effect of multipathed traffic that is spread unevenly between initiator ports.  Note that when the change occurs, connectivity is not lost, but pathing may become sub-optimal.

Affected versions:

All supported versions of VMware vSphere (ESXi) hosts

Storage Center OS version 6.6 and later


 

Resolution:

Reconfigure the path selection policy default for the VMW_SATP_ALUA module. For example, if the previous policy default was set to VMW_PSP_RR (Round Robin), modify the VMW_SATP_ALUA SATP module either via VMware PowerCLI or via the host’s ESXi shell as shown below.

ESXi Shell commands:

• Fibre Channel, iSCSI, or Direct Attach
  • For Storage Center OS version 6.5 and earlier

esxcli storage nmp satp set -P VMW_PSP_RR -s VMW_SATP_DEFAULT_AA

• • For Storage Center OS version 6.6 and later

esxcli storage nmp satp set -P VMW_PSP_RR -s VMW_SATP_ALUA

• FCoE
  • For Storage Center OS version 6.5 and earlier

esxcli storage nmp satp rule add -R fcoe -s VMW_SATP_DEFAULT_AA

• • For Storage Center OS version 6.6 and later

esxcli storage nmp satp rule add -R fcoe -s VMW_SATP_ALUA

Notes:

• Both SATP modules can have VMW_PSP_RR (Round Robin) set as default at the same time
• Ideally the VMW_SATP_ALUA module will have default set to VMW_PSP_RR prior to the upgrade to Storage Center OS version 6.6 or later, however this can be changed on all the datastores via script retroactively.
• If the previous path selection policy was VMW_PSP_FIXED for purposes such as with Live Volume, that policy will need to be modified on each of the volumes as well.

Additional information regarding multipath module best practices, as well as scripting examples to automate these recommended changes, are available in the Dell Storage Center Best Practices with VMware vSphere 5.x and 6.x documents available on Dell Tech Center. https://www.dell.com/support/article/SLN312469/