Importance of Path Change Settings in VMware

[matthiasgoodman77]

I believe it is either by IOPS or bytes. Whichever is the last one set will be the policy so setting both would be unnecessary. Of course I could be wrong.

This probably explains the differing results since most seem to be setting bytes first then setting IOPS to 0. Effectively it is just using poor mans LQD in that case with IOPS at 0.

We saw our best improvements by setting IOPS to 0.

[boyler0571]

(I posted this is another thread but just wanted to cross-post here as well, since this thread comes up first in Google search.)  FYI: I tried configuring both iops=0 and bytes=0 for all Nimble volumes using the above CLI commands, which worked until the next reboot.  After the reboot, iops stayed at 0, but bytes returned to the default of 10485760.  This appears to be by design; the PSP policy can be either based on IOPS or Bytes but not both (pick one or the other).  There doesn't seem to be any reason to configure bytes=0; the consensus seems to be that setting iops=0 for Nimble volumes is a best practice.  Also, I was able to find a very simple and elegant command line to set all Nimble datastores (including new ones added after-the-fact) to default to the Round Robin PSP with the PSP policy iops=0.  After issuing the following command, reboot the ESXi host and you will see that all Nimble volumes (including new ones) will default to Round Robin with iops=0:

esxcli storage nmp satp rule add --psp=VMW_PSP_RR --satp=VMW_SATP_ALUA --vendor=Nimble --psp-option="policy=iops;iops=0"

Note that if you previously configured a user-defined SATP rule for Nimble volumes to simply use the Round Robin PSP (per the Nimble VMware best practices guide), you will first need to remove that simpler rule, before you can add the above rule, or else you will get an error message that a duplicate user-defined rule exists.  The command to remove the simpler rule is:

esxcli storage nmp satp rule remove --psp=VMW_PSP_RR --satp=VMW_SATP_ALUA --vendor=Nimble

Hope this helps (and makes its way into the Nimble VMware best practices guide!).

Bill

[Nick_Dyer]

Hi Bill,

Yes you are correct - these path changes get reset by default when a host reboots (good old VMware!).

The great thing is now that Nimble OS 2.0 is GA it's possible to use Nimble Connection Manager which replaces the need for these scripts and also maintains settings after reboots... (requires VMware Enterprise or Enterprise Plus licensing though).

[boyler0571]

Thanks Nick!  Does Nimble Connection Manager require that the Nimble array(s) are on firmware 2.x, or will it still work with Nimble arrays on firmware 1.4.x?

[Nick_Dyer]

NCM for VMware does indeed require firmware 2.0 on your Nimble array for it to work as required. More info with regards to 2.0 should be posted up here shortly