[MVLUG] Software Raid

Samat K Jain lists at samat.org
Mon Sep 27 03:51:43 MDT 2010

On Monday, September 27, 2010 12:18:47 am Jonathan Lindsey wrote:
> "On the Linux XFS implementations, compatibility issues between different
> architectures exists due to journaling-optimization. This can be solved by
> running xfs_repair (to clean the journal) before mounting the file system
> on a different architecture."
> http://ubuntuforums.org/archive/index.php/t-285858.html

An error on my part—there *IS* one one XFS architecture-specific limitation—
the contents of XFS's uncommitted journal (called the "log" in XFS lingo, 
which is why you've had trouble finding information on the topic) is stored in 
an architecture-specific manner (presumably for performance reasons).

That is, if you uncleanly mount an XFS filesystem (i.e. crash, yank a disk 
out, etc), the contents of the log will be uncommitted and you may have 
problems mounting it on a different architecture.

This is what happened in the mentioned forum topic. You can see the line about 
an attempt to start XFS recovery, after which the XFS driver crashes.

This is easy to avoid. Don't let your filesystems unmount uncleanly, and if 
you do, re-mount it on the same architecture first to make sure everything is 
OK. If you can't, you run the xfs_repair command (as the post mentions) which 
will either attempt to replay the log, or zero it (you will lose data).

Samat K Jain <http://samat.org/> | GPG: 0x4A456FBA

Sometimes it is entirely appropriate to kill a fly with a sledge hammer.
-- Major I L Holdridge (625)
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