Re: Question: Does XFS journal data or only metadata?

Re: Question: Does XFS journal data or only metadata?

[Michal Szymanski]

Steve Lord <lord <at> xfs.org> writes:

> > OK - After looking at the strace I checked the _other_ superblocks. 
> > As I only altered SB0, the other superblocks SB1+ still contains the  
> > old logstart value.
> > 
> > Wrote "logfile 0" to SB 0 - SB 15, and it all works! :)
> > 
> > It this the way to do it, or am I missing something obvious?
> > 
> 
> That is the way to do it, the tools are more picky than they used
> to be about this. Which is why getting the facility built into
> the tools would help a lot - since it would do the fixup of all
> superblocks itself.
> 
> Steve

This is a pretty old thread but I have not found anything newer, so
maybe somebody is still watching.

I went through internal->external log procedure as described here and
linked-to articles a few years  ago and it worked fine. These days I got
into similar problem after reconfiguring a disk which holds the 
external log for a XFS partition. The question to the gurus is
following:

Is it possible to migrate an external log to internal if the XFS
filesystem was originally created without  an internal log, i.e. it was
put on external device straight at mkfs.xfs invocation? 

xfs_growfs still says, after 7 years, at least in the man page, that
-l/-i/-x options are not implemented.  Is it really so?

regards, Michal.

PS. Just to comment on multiple SBs issue. The need for manually rewrite
ALL superblocks' data was  mentioned in the first comment (by Eric
Sandeen) to the excellent HOWTO written by Steve Lord in 
http://oss.sgi.com/archives/xfs/2003-11/msg00683.html 
The thread is titled:
It just begs the question everywhere: how to move a journaling
log to a new device?


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Re: Question: Does XFS journal data or only metadata?

[Dave Chinner]

On Thu, Feb 09, 2012 at 11:45:38AM +0000, Michal Szymanski wrote:
> I went through internal->external log procedure as described here and
> linked-to articles a few years  ago and it worked fine. These days I got
> into similar problem after reconfiguring a disk which holds the 
> external log for a XFS partition. The question to the gurus is
> following:
> 
> Is it possible to migrate an external log to internal if the XFS
> filesystem was originally created without  an internal log, i.e. it was
> put on external device straight at mkfs.xfs invocation? 

Not easily. The log region needs to be contiguous, and removed from
the free space btrees, which means it is a tricky operation to do.
It's possible that all you need to do is find enough contiguous free
space somewhere and point the superblock at that (with xfs_db), then
run repair to fix up the free space trees. I would not try this on a
filesystem that holds data you care about, though, until you know
whether it works...

> xfs_growfs still says, after 7 years, at least in the man page, that
> -l/-i/-x options are not implemented.  Is it really so?

Very few people ever ask about doing this or need it and it's quite
complex to implement and test, so it's never been done. It will
probably stay unimplemented until someone who really needs it helps
implement it.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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