VMWARE PLUGABLE STORAGE ARCHITECTURE

Pluggable Storage Architecture (PSA)

To manage storage multipathing, ESX/ESXi uses a special VMkernel layer, Pluggable Storage Architecture (PSA). The PSA is an open modular framework that coordinates the simultaneous operation of multiple multipathing plugins (MPPs). PSA is a collection of VMkernel APIs that allow third party hardware vendors to insert code directly into the ESX storage I/O path. This allows 3rd party software developers to design their own load balancing techniques and failover mechanisms for particular storage array. The PSA coordinates the operation of the NMP and any additional 3rd party MPP.

Features

• There are two NMP sub plugin->SATPs (Storage array type plugin) and PSP (path selection plugin)

• Either we can create third party MPP to replace  default NMP or we can replace the sub plugins (SATP/PSP) under NMP

• 3rd party MPP can exist along with native NMP

Vmware SATP

• This module is for selecting the failover path based on the class of storage ,this module can do failover and detect path based on storage

• monitor and report health of the path and perform array specific action for storage failover

• There is a SATP  rule set specific for storage models and the current  rule can be found by

      esxcli storage nmp satp rule list

• There is a default path selection policy of each SATP this is displayed by

           esxcli storage nmp satp list

Vmware PSP

This sub plugin is for the Path selection policy for the i/o data based on the SATP

There will be a default PSP associated with different SATP and we have the option to change the default PSP

Different type of PSP

VMW_PSP_MRU

Most recently used path is selected and onec it become unavailbel next path is selected and once the unavailable path become available it will not transfer back

This is the default policy for active active array

VMW_PSP_FIXED

Host uses fixed path either we can specify explicitly or it uses first working pathand on unavailability it will select new path. In case of explicitly chosen it will remain as such not failover will occur.

This is the default policy of  active -active array

VMW_PSP_RR

This is used for load balancing and used with all type of array

Best practice for Storage model from specific vendor

1.Check in vmware HCL about the supported PSP and SATP rules and once clear change else put        default

2.Check  SATP rule corresponding to the specific vendor

        esxcli storage nmp satp rule list

3.Check PSP for the corresponding  SATP

          esxcli storage nmp satp list

4.If you want to change the PSP  rule for the SATP corresponding to specific vendor and model

esxcli storage nmp device list -d <device-naa-value>

this will give the vendor and model for the specific lun from the storage

esxcli storage nmp satp rule add -V <vendor> -M "<model>" -P <psp> -s satp>

this will change the default rule

esxcli storage nmp satp rule list

check SATP rule again

Conclusion

Here you can see that there is a default rule for the vendor A and there is a rule for the vendor A with model B.The advantage is that we can keep the default policy as such for the vendor and we can i n addition add policy for specific model for the vendor

Links helpful

https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1011375

http://www.gabesvirtualworld.com/changing-satp-claimrules-specific-storage-configurations/