[LU-17300] Avoid creating new dir/file/object on newly added MDT/OST

Cloners — Mon, 22 Jan 2024 06:00:06 +0000

When a new MDT is added to a filesystem without no_create then the DNE MDT auto-balance is enabled, then a new subdirectory could be created on the new MDT relatively quickly after it is added to the filesystem. However, it might take a few seconds for the addition of the new MDT to be propagated across all of the clients, so there is a small risk that an MDT is holding a subdirectory that another client is not yet aware of.

I think there are two relatively simple solutions to this:

don't consider a new MDT for subdirectory creation for, say, 30s after it appears in the config, to give other clients a chance to discover it
if a new MDT is used for a subdirectory that is not in the config, then the client should pull the config from the MGS to see if it was newly added.

The similar situation exists with new OSTs added to an existing files, where the MDS is notified about an OST addition and allocates an object to a file, but the client has not yet been notified about the new OST and will return an error accessing the file. The solution in this case is the same - avoiding to use a new OST for object allocation for ~30s after the OST is added, and similarly for clients to pull the config from the MGS to see if the OST was newly added.

This ticket is tracking the first issue - don't create new subdirs/files/objects on newly-added targets. LU-17344 is separately tracking the client more gracefully handling the presence of subdirs/files/objects on an MDT or OST that it doesn't know about.

Whamcloud Community JIRA

[LU-17300] Avoid creating new dir/file/object on newly added MDT/OST