Storwize and ESX: change default path selection to RR

Round robin is now an acceptable psp for storwize. However if you don't want to change the psp for every lun you create, it might be handy to adjust the default satp for svc so that it uses RR for every (new) lun it detects.

First of all, lets see all the possible path selection protocols we can use (PSP)
~ # esxcli storage nmp psp list
Name Description
------------- ---------------------------------
VMW_PSP_MRU Most Recently Used Path Selection
VMW_PSP_RR Round Robin Path Selection
VMW_PSP_FIXED Fixed Path Selection

We can see the default MRU for storwize/svc, which we are going to change to RR

First of all we can see that ESX will use a certain SATP if it detects an SVC / Storwize
~ # esxcli storage nmp satp rule list
Name Device Vendor Model Driver Transport Options Rule Group Claim Options Default PSP PSP Options Description
------------------- ------ ------- ---------------- ------ --------- -------------------------- ---------- ----------------------------------- ----------- ----------- --------------------------------------------------------------------------
VMW_SATP_SVC IBM 2145 system

Conveniently this is VMW_SATP_SVC . We can now check which default PSP is associated with this SATP by executing the list rule
~ # esxcli storage nmp satp list
Name Default PSP Description
------------------- ---------------- ------------------------------------------

You can see that by default MRU is chosen. We can change with the following command
esxcli storage nmp satp set --default-psp yourpsp --satp yoursatp

So execute
~ # esxcli storage nmp satp set --default-psp VMW_PSP_RR --satp VMW_SATP_SVC
Default PSP for VMW_SATP_SVC is now VMW_PSP_RR

Now reboot your server, the paths should be reclaimed with RR

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