[LU-15314] set default max-inherit to 3 for default dir stripe policy if stripe count is not 0 or 1

• Type: New Feature
• Resolution: Fixed
• Priority: Critical
• Fix Version/s: Lustre 2.15.0
• Affects Version/s: Lustre 2.7.0
• Labels: easy
• Assignee: Feng Lei
• Reporter: Feng Lei

Description

From LU-15307 by adilger
 
In addition to limiting the stripe count used when selecting "-c -1" it also makes sense to return an error from "lfs setdirstripe" when creating a default directory striping that has a stripe count > 1 but does not have max-inherit set. There have repeatedly been problems hit when a filesystem is configured with "lfs setdirstripe -c N -D $MOUNT" (for any N > 1) causing REMOTE_PARENT_DIR to be filled or have tens of millions of entries, excessive MDT inode usage, performance issues, etc.

With automatic DNE MDT space balancing (LU-13440) the need to stripe directories by default is almost completely eliminated. It should still be possible to set this by explicitly specifying --max-inherit=N, but this is too dangerous to let users shoot themselves in the foot by accident by what "seems" like a good idea but is actually very bad over time.
Edit

Issue Links

• is related to: LUDOC-501 Document (dir)stripe limits
• is related to: LU-15307 Option to set max directory stripe count per filesystem
• is related to: LU-14792 DNE3: enable filesystem-wide default LMV
• is related to: LU-13440 DNE3: limit directory default layout inheritance