[LU-12867] DNE3: new DNE2 hash function to handle rsync temporary filename

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Assignee: Lai Siyao
• Reporter: Andreas Dilger

Description

When copying or resyncing a file with rsync it will create a temporary pathname for the target file, copy the data into the temporary pathname, and then rename the file over the original in order to avoid damaging the original file if the rsync is interrupted.

$ rsync twoshoes.dilger.ca:/myth/tv/2103_20150920012700.mpg .
^Z
ls -l .2*
 3328 -rw-------  1 adilger 2883584 Oct 16 09:10 .2103_20150920012700.mpg.gyCFCs

It is creating a temporary file with a leading "." and a trailing ".XXXXXX" using mktemp(3) or similar. When the temporary filename is renamed to the target filename in a striped directory, it would likely move to a new MDT and become a remote entry. That causes overhead due to invoking remote rename operations, and leaves a lasting performance impact due to the remote directory entry.

It would be useful to add a new hash function (e.g. FNV_1a_TEMP) that will handle the case of filenames with a leading "." and trailing ".xxxxxx" 6-8 chars after the "." by dropping those parts of the filename and using the remaining characters for the hash, on the assumption that the final filename would be the just the remaining characters. That will keep the rename to be local to a single MDT in most cases, and not be worse than the current case.

Issue Links

• is related to: LU-13481 sanity test_33h: MDT index mismatch 5 times
• is related to: LU-11025 DNE3: directory restripe

Comments

[Andreas Dilger]

This functionality was included into the patch https://review.whamcloud.com/36775 "LU-11025 dne: introduce new directory hash type: 'crush'" which landed for 2.14.

[Gerrit Updater]

Lai Siyao ([e-mail]) uploaded a new patch: https://review.whamcloud.com/36799
Subject: LU-12867 dne: place temp file on MDT where target is
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 92d3050f760f00f22e85abdc456fe8ccb2d6e7f4

[Andreas Dilger]

I believe that MPIFileUtils dcp is also creating temporary filenames for the target, so it would be good to handle this case as well, possibly modifying the MPIFileUtils code to make this filename pattern more easily detected.