[lustre-discuss] Usage for lfs setstripe -o ost_indices

Patrick Farrell paf at cray.com
Fri Nov 9 13:03:21 PST 2018

“I am not able to specify -o to an existing file.”
Yes, that’s expected - As with any other setstripe command, you cannot apply it to existing files which already have stripe information.  (The exception is files created with LOV_DELAY_CREATE or mknod(), which do not have striping information until they are written to.)
If you instead use lfs setstripe -o to create a file, that should work.

  *   Patrick

From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of "Ms. Megan Larko" <dobsonunit at gmail.com>
Date: Friday, November 9, 2018 at 2:20 PM
To: Lustre User Discussion Mailing List <lustre-discuss at lists.lustre.org>
Subject: Re: [lustre-discuss] Usage for lfs setstripe -o ost_indices

Responding to A. Dilger (orig e-mail copied below)
I am not sure what the overall objective is trying to achieve in specifically identifying to which OSTs to write; it was a question from one in our user community.   I am not able to specify -o to an existing file.  I have not tried to use the lustrelibapi to specify OST layout during the write.
I concur that LU-8417 points out a very significant disadvantage to having users employ the -o option to "lfs setstripe" and that using Lustre Pools is a better idea for the file system. (I'm speculating that perhaps the users themselves want to be able to create such Lustre Pool-like areas and currently only sysadmins may create Lustre Pools.  Avoid the middle-man/woman!  Smile!)
Let me get back to my users to better understand what it is that needs to be done causing them to wish to invoke the -o option to "lfs set-stripe".

A. Dilger wrote:
[Image removed by sender.]
Andreas Dilger

12:51 PM (2 hours ago)

to Mohr, me, Lustre
[Image removed by sender.]

This is https://jira.whamcloud.com/browse/LU-8417 "setstripe -o does not work on directories", which has not been implemented yet.

That said, setting the default striping to specific OSTs on a directory is usually not the right thing to do. That will result in OST imbalance.

Equivalent mechanisms include OST pools (which also allow a subset of OSTs to be used, unlike -o currently does), and has the benefit of labeling files with the pool to find them easier in the future (eg. for migrating out of the pool).

What is the end goal that you are trying to achieve?

Cheers, Andreas
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