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Re: Optimal XFS formatting options?

To: xfs@xxxxxxxxxxx, stan@xxxxxxxxxxxxxxxxx
Subject: Re: Optimal XFS formatting options?
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Tue, 17 Jan 2012 10:19:55 +0100
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
In-reply-to: <4F14EBAF.10808@xxxxxxxxxxxxxxxxx>
Organization: it-management http://it-management.at
References: <33140169.post@xxxxxxxxxxxxxxx> <20120116231121.GB6922@dastard> <4F14EBAF.10808@xxxxxxxxxxxxxxxxx>
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On Dienstag, 17. Januar 2012 Stan Hoeppner wrote:
> Thanks for the correction/reminder Dave.  So in this case the first
> sector of the first partition would need to reside at LBA1280 in this
> array (655360 byte stripe width, 1280 sectors/stripe), as the
> partition table itself is going to occupy some sectors at the
> beginning of the first stripe.  By creating the partition at LBA1280
> we make sure the first sector of the XFS filesystem is aligned with
> the first sector of the 2nd stripe.

There's one big problem with that: Many people will sooner or later 
expand and existing array. If you add one drive, all your nice stripe 
width alignment becomes bogus, and suddenly your performance will drop.

There's no real way out of that, but three solutions come to my mind:
- backup before expand/restore after expand with new alignment
- leave existing data, just change mount options so after expansion at 
least new files are going to be aligned to the new stripe width. 
- expand array by factors of two. So if you have 10 data drives, add 10 
data drives. But that creates other problems (probability of single 
drive failure + time to recover a single broken disk)

mit freundlichen Grüssen,
Michael Monnerie, Ing. BSc

it-management Internet Services: Protéger
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