[LU-15850] MDT QOS should always be used for round-robin directories.

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Affects Version/s: Lustre 2.15.0
• Labels: MON
• Assignee: Lai Siyao
• Reporter: Andreas Dilger

Description

The MDT QOS should always be used for subdirectories created in a parent that has round-robin activated, if the MDT space balance exceeds qos_threshold_rr. Otherwise, subdirectories in that directory tree will suddenly change from r-r to being "sticky" on a single MDT, which significantly changed the behavior and load distribution across MDTs. The "threshold by depth" should only be used for directories that would otherwise have always been created on the parent already.

Related to this, it should be possible to tune the weighting of subdirectories by depth so that this can be adjusted without recompiling the code.

Issue Links

• is related to: LU-13439 DNE3: MDT QOS tuning to avoid full MDTs completely
• is related to: LU-14762 qos subdirectory creation stay on parent MDT if less full than average doesn't work as expected
• is related to: LU-13417 DNE3: mkdir() automatically create remote directory on MDS which has more space
• is related to: LU-15910 ROOT default LMV is not working for subdirectory mount
• is related to: LU-13440 DNE3: limit directory default layout inheritance