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Re: Is xfs defrag *reliably* aligned to stripes?

To: Spelic <spelic@xxxxxxxxxxxxx>
Subject: Re: Is xfs defrag *reliably* aligned to stripes?
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 23 Nov 2010 10:07:28 +1100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4CEAC203.9040800@xxxxxxxxxxxxx>
References: <4CEAC203.9040800@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Mon, Nov 22, 2010 at 08:18:27PM +0100, Spelic wrote:
> Hello xfs people,
> does the xfs defrag (xfs_fsr, I think) reliably aligns files to stripes?

No, the allocator does best effort attempts only.

> Does it do that? Will it do that in the future?

If the filesystem has large enough contiguous free space extents, it
will align the initial allocation to stripe unit, but once you age
the filesystem there is no guarantee this will be possible. use
"xfs_bmap -vvp" to look at the alignment of files.

Of course, this all only works if you mkfs your filesystem with
sunit/swidth or su/sw parameters....


Dave Chinner

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