xfs_check and xfs_repair internal working details

xfs_check and xfs_repair internal working details

[Fong Vang]

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:

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?

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.

If anyone can provide more insight into xfs_check and repair, it would be
greatly appreciated.

Thank you.


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Re: xfs_check and xfs_repair internal working details

[David Chinner]

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