Re: Is it possible to change sunit of log section post-mkfs

Brian Foster
2015-11-03T19:39:52Z

On Tue, Nov 03, 2015 at 08:22:33PM +0100, Michael Weissenbacher wrote:
> Hi Brian!
>
> On 2015-11-03 14:02, Brian Foster wrote:
> > I don't believe there's any supported way to do this.
> Well, at least i didn't miss anything in the documentation :-)
>
> On 2015-11-03 14:02, Brian Foster wrote:
> > Out of curiosity,
> > I just tried an experiment to modify the superblock logsunit via xfs_db
> > and run repair to zero the log. That seemed to work in terms of taking
> > effect on the subsequent mount, but that's certainly not something I
> > would suggest to do in production.
> Ok, so it would definitely be too risky for a production system.
>
> On 2015-11-03 14:02, Brian Foster wrote:
> > Note that mkfs aligns the physical
> > log based on the stripe unit as well, so it wouldn't really have the
> > same effect anyways.
> TBH, i didn't quite understand that part :-)
> Are you saying, even if i would modify the log's sunit size using
> xfs_db, it would still not be aligned correctly?
>

Yes, exactly. mkfs uses the log stripe unit to decide where to put the
log on disk. If the log itself is not aligned, then there's little use
in aligning the writes to the log.

Brian

> thanks,
> Michael
>
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