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Re: xfs_check and xfs_repair internal working details

To: Fong Vang <sudoyang@xxxxxxxxx>
Subject: Re: xfs_check and xfs_repair internal working details
From: David Chinner <dgc@xxxxxxx>
Date: Tue, 22 Apr 2008 08:02:21 +1000
Cc: xfs@xxxxxxxxxxx
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On Mon, Apr 21, 2008 at 12:57:22PM -0700, Fong Vang wrote:
> I would like to find how how xfs_check and xfs_repair do their work
> internally.  I need to find answers to the following questions:

Read the source code - the answers are all there.

> a) assuming the amount of data is the same for file systems, does it take
> longer for xfs_check and xfs_repair to check/repair a file system with a lot
> more files than one that has fewer?  Assuming two file systems are 1TB each
> completely filled.  One of the file systems is filled with very large files
> while the other one is filled with very small files, does it take longer to
> check and repair the latter?

The obvious thing here is to try it and measure it. Or perhaps go download
the slides/video/audio from this talk:

        http://linux.conf.au/programme/detail?TalkID=135

The slides:

        
http://mirror.linux.org.au/pub/linux.conf.au/2008/slides/135-fixing_xfs_faster.pdf

And that should answer your question.

> b) does xfs_check and repair check only the used blocks or does it check
> everything?  I think there's a free list as well so I'm assuming it checks
> that list as well.

Pretty much everything is checked and/or repaired. If it is not, then that's
a bug.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group


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