[LU-3479] add OBD_INCOMPAT_FID on OST when FID-on-OST is enabled?

Tue, 14 Dec 2021 22:56:25 +0000

It came up during discussion of unified targets design that we should consider setting the OBD_INCOMPAT_FID feature flag in the last_rcvd file, so that if the OST is used for DNE it can't be mounted by an old version of Lustre that doesn't support FID-on-OST. That would avoid the problem of unintentionally mounting the OST with an old version of the code and the FID_SEQ_NORMAL objects are no longer accessible.

However, this would also prevent downgrading the filesystem from 2.4+ DNE to 2.1.x. By the time the MDS is running some non-DNE release, then the inodes that reference the FID_SEQ_NORMAL objects on the other MDTs will not be visible anymore, so it is no more harmful if OST objects cannot be accessed, so that would be a reason not to set OBD_INCOMPAT_FID to cause gratuitous incompatibility... Thoughts?

Whamcloud Community JIRA

[LU-3479] add OBD_INCOMPAT_FID on OST when FID-on-OST is enabled?