When VMware released vSphere 4 last year, one of the changes they made was a completely re-written software iSCSI initiator. This was done to optimize performance which is great considering how popular iSCSI SANs have become. They also gave the ability to use Round Robin MPIO (mutlipathing) in the software initiator in addition to Fixed Path and MRU which were previously available.
I’m working on a vSphere implementation using Dell EqualLogic SANs and wanted to configure Round Robin on all of my datastores. Dell has a great whitepaper on how to set this up, but unfortunately the document fails to mention one key thing: this doesn’t change the default path selection plugin (PSP) from Fixed to Round Robin. That means that you’ll have to set the multipathing policy to Round Robin on all of your existing datastores and will have to remember to do that on all future datastores. When you’ve got multiple ESX hosts with lots of datastores this can quickly become a pain.
Luckily there is a way to force the default multipathing policy to Round Robin. The following commands can be used to change the default PSP to Round Robin as well as configure round robin specifically for the EqualLogic provider. These commands can be entered at the Service Console or via the vSphere CLI 4.0:
esxcli nmp satp setdefaultpsp –satp VMW_SATP_DEFAULT_AA –psp VMW_PSP_RR
esxcli nmp satp setdefaultpsp –satp VMW_SATP_EQL –psp VMW_PSP_RR
esxcli corestorage claimrule load
esxcli corestorage claimrule run
Note that “satp” and “psp” are preceded by two dashes and not a single dash as it appears in this blog post.
Once you enter those commands (no rebooting required) any volume you add, either new or existing, will use Round Robin MPIO by default.