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Is xfs defrag *reliably* aligned to stripes?

To: xfs@xxxxxxxxxxx
Subject: Is xfs defrag *reliably* aligned to stripes?
From: Spelic <spelic@xxxxxxxxxxxxx>
Date: Mon, 22 Nov 2010 20:18:27 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100713 Thunderbird/3.0.6
Hello xfs people,

does the xfs defrag (xfs_fsr, I think) reliably aligns files to stripes?

There is one scenario which requires this: if you make raw disk images for virtual machines, you want such files to be reliably aligned to stripes.

Even if a complete defrag for one file is not possible because there is no contiguous free space (you remain e.g. with 2 trunks for one of such files you still need to ensure that every trunk begins exactly at the beginning of a stripe and ends exactly at the end of a stripe.

This is the only way to be able to align the guest filesystems to the RAID, inside the virtual machine. (obviously this also requires some work by the system administrator because he needs to ensure that partitions inside the guest also are offsetted by multiples of the stripe size, ok, but it's still anyway needed that xfs_fsr guarantees total alignment to the stripes like I described)

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

Thank you

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