Changing Path Selection Policy (PSP)

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VirtuCache inserts a Path Selection Plugin (PSP) in VMware Multi Path Plugin (MPP). When you install VirtuCache, VirtuCache makes a note of the VMware PSP you have currently, and then it replaces the VMware PSP with VirtuCache PSP. So say you had the VMW_PSP_MRU, VirtuCache will replace it with VNX_PSP_MRU.

We use the Pluggable Storage Architecture APIs from VMware to intercept storage IO in the host. We need to intercept storage IO at the host to make a decision of where to serve the data from (for reads) and to write all recent writes to the in-host cache media.

Please do not revert the VNX_PSP* back to VMW_PSP* on the fly. The only way to cleanly revert the VNX_PSP* back to the original VMware PSP (VMW_PSP*) is to uninstall VirtuCache caching driver from the host.

You can change one VNX_PSP_* (VNX_PSP_RR, VNX_PSP_Fixed, or VNX_PSP_MRU) with another VNX_PSP_* on the fly without requiring maintenance mode and while storage IO is happening. However, there should really be a very good reason why you want to do this. The PSP recommendation usually comes from the storage appliance vendor, in terms of whether you would go with Fixed, MRU, or RR PSP policy, and you should adhere to those recommendations. It doesn’t matter to VirtuCache which specific PSP policy you apply so long as it is a VNX_PSP_* policy. Also as far as the storage appliance goes, VNX_PSP* is the same as VMW_PSP*.

Sometimes VMware automatically replaces the Administrator assigned PSP with MRU PSP, since MRU is the default VMware PSP. If this is the case in your environment then please follow this link to understand why this happened and its resolution.

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