In a distributed and clustered environ, which kvstores need migration to wiredTiger prior to upgrading to 9.0.4?

[Glasses2]

I am about to upgrade 8.1.3 distributed / clustered environment to 9.0.4.

Per Docs> 

• Migrate your App Key Value Store storage engine from the Memory Mapped (MMAP) storage engine to the Wired Tiger storage engine, and update your MongoDB version from 3.6 to 4.2. These updates are required in Splunk Enterprise 9.0. See Migrate the KV store storage engine in the Admin manual to plan your migration.
• Back up your App Key Value Store (KV Store) databases prior to starting an upgrade. If you run version 7.1 and lower of Splunk Enterprise, you must stop Splunk Enterprise instances first.

I am going to do this part prior to the Upgrade.

I inherited this deployment so IDK where all the KVstore(s) are located or which nodes have a default KVstore needing the same migration/upgrade (e.g. MC or DS).

My Environment> SHC(4), SHC-deployer, IDXCM, IDXC(10), MC/LM, DS, HFs, UFs

Any advice appreciated.  If someone can share knowledge such as, how to validate KVstore locations and which KVstore(s) need update...  that would help.

Thank you

Thank you

[Glasses2]

I think, better safe than sorry, looks like some apps use KVstores... 

[richgalloway · Accepted solution]

Indexers and UFs never use KVStore so no upgrades are needed there.

Definitely upgrade the SHs.

I'm on the fence regarding SHCD, CM, MC/LM, and DS.  Absent advice to the contrary, I'd play it safe and upgrade them.