[LU-10258] lfs mirror command to read/write specific mirror copy

• Status: Resolved
• Project: Lustre
• Fix Version/s: Lustre 2.13.0, Lustre 2.12.3
• Type: Improvement
• Priority: Minor
• Reporter: Andreas Dilger
• Assignee: Zhenyu Xu
• Resolution: Fixed
• Labels: FLR2

Description

It would be useful to add an "lfs open [--ifcomp=<component_id>] [--ofcomp=<component_id>] <command>" that opens the stdin and/or stdout with the specified component ID values, so that e.g. "dd" could be used as a resync tool for stale components, or other arbitrary commands (e.g. MPI file utils for parallel resync, HSM tools for archive handling, etc).

Also useful would be to open a specific mirror number for whole-file access, instead of just a single component. That would be something like "--ifrepl=" and "--ofrepl=" options.

Issue Links

• is related to: LU-5170 lfs usability
• is related to: LU-9771 FLR1: Landing tickets for File Level ...
• is related to: LU-11245 add 'lfs mirror dump' to dump a mirro...
• is related to: LU-10177 DoM: manual migration MDT-OST
• is related to: LU-11421 DoM: manual migration OST-MDT, MDT-MDT
• is related to: LU-13831 lfs mirror command to open a specific...

Comments

[Jinshan Xiong (Inactive)]

Should we support the command like lfs mirror dd [--if=<mirror_id>] [--of=<mirror_id>] instead? If -if is not existing, it will read from stdin; if of is not existing, it will write to stdout. Multiple -off can be supported if necessary. This is more like unix and is able to use pipe to chain commands.

The problem with --ifcomp is that sometimes components are not started from beginning of the file; neither are components perfectly aligned. Therefore it would be hard to define the semantics clearly.

[Jinshan Xiong (Inactive)]

From https://review.whamcloud.com/#/c/29100/23/lustre/doc/lfs-mirror-verify.1

Andreas Dilger Nov 22 9:37 PM

Not for this patch, but it would be interesting to use something like:
lfs open --ifrepl=N <file> | diff <file> /dev/stdin
(or with cmp) to be able to find what is different between two replicas.
That makes me wonder if we would want some special open syntax some time later, like:
diff <file> "<file>;N"
to allow opening replica N directly from the command line? This uses the same naming to be consistent with VAX VMS file versions, and has the benefit that virtually no files will have ';' in the name because this is a shell metacharacter. The drawback is that accessing non-primary components would always need to escape or quote the file name, which is probably OK if it isn't commonly used. We might use something like ",,N" to allow easier usage, but have a higher risk of collisions with existing filenames.

[Andreas Dilger]

The problem with --ifcomp is that sometimes components are not started from beginning of the file; neither are components perfectly aligned. Therefore it would be hard to define the semantics clearly.

I think there are legitimate use cases for opening a component and allowing writes outside of the component start/end. For example, migrating a large DoM file from the MDT to the start of an OST object and freeing up space on the MDT.

[Andreas Dilger]

I wonder if we should rename this to "lfs mirror write" and rename "lfs mirror dump" to "lfs mirror read" for consistency?

[Gerrit Updater]

Bobi Jam ([e-mail]) uploaded a new patch: https://review.whamcloud.com/33219
Subject: LU-10258 lfs: lfs mirror write command
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 08c8accd22dc1021da3a0c37d8c6a33f1bf44607

[Gerrit Updater]

Bobi Jam ([e-mail]) uploaded a new patch: https://review.whamcloud.com/33220
Subject: LU-10258 lfs: lfs mirror copy command
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 075a96702fe89c37a9a4e1c11401a75d173dfdad

[Gerrit Updater]

Oleg Drokin ([e-mail]) merged in patch https://review.whamcloud.com/33219/
Subject: LU-10258 lfs: lfs mirror write command
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 14171e787dd00902af7c9edf10a6b54aab45f7b2

[Gerrit Updater]

Oleg Drokin ([e-mail]) merged in patch https://review.whamcloud.com/33220/
Subject: LU-10258 lfs: lfs mirror copy command
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: c6e7c0788d7cd766880d12eae6679782283dc479

[Peter Jones]

Landed for 2.13

[Gerrit Updater]

Jian Yu ([e-mail]) uploaded a new patch: https://review.whamcloud.com/36193
Subject: LU-10258 lfs: lfs mirror copy command
Project: fs/lustre-release
Branch: b2_12
Current Patch Set: 1
Commit: 00a5d4a04710b5c939b81c422e7b800471ffd83d

[Gerrit Updater]

Oleg Drokin ([e-mail]) merged in patch https://review.whamcloud.com/36193/
Subject: LU-10258 lfs: lfs mirror copy command
Project: fs/lustre-release
Branch: b2_12
Current Patch Set:
Commit: 24f181513fb14f111455ec113d69a6ce5b50cf56