[LU-14459] DNE3: directory auto split during create

• Type: Improvement
• Resolution: Unresolved
• Priority: Major
• Labels: dne3
• Assignee: Lai Siyao
• Reporter: Andreas Dilger

Description

Directory auto-split should be done when the dir_split_count is hit during file creation to minimize the number of entries that need to be moved, rather than afterward. Otherwise, the entries are being created on a single MDT first, and only being migrated on a later directory access. This is sub-optimal for two reasons:

• the initial file creation will be limited to a single MDT and not distribute the load across multiple MDTs, so just entry migration will still leave all the inodes on the original MDT
• the post-creation migration will need to move many more files/entries to the other MDTs than if the files are created on the correct MDT to start with

Issue Links

• duplicates: LU-14467 Allow split metadata across MDTs during file creation
• is related to: LU-14464 Auto restripe triggers with none of the reasons
• is related to: LU-14466 metadata performance slows if the metadata migration is process is running
• is related to: LU-15692 performance regressions for files in stripe directory
• is related to: LU-15720 imbalanced file creation in 'crush' striped directory
• is related to: LU-15502 mkdir returns -EBADF if default LMV is set in 2.12 client <-> 2.14 MDS system
• is related to: LU-14146 Massive directory metadata operation performance decrease
• is related to: LU-11025 DNE3: directory restripe