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Re: XFS Logs on Another Device

To: David Lloyd <lloy0076@xxxxxxxxxxx>
Subject: Re: XFS Logs on Another Device
From: Eric Sandeen <sandeen@xxxxxxx>
Date: Fri, 25 Oct 2002 21:23:38 -0500 (CDT)
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <20021026105131.6d692c0d.lloy0076@xxxxxxxxxxx>
Sender: linux-xfs-bounce@xxxxxxxxxxx
On Sat, 26 Oct 2002, David Lloyd wrote:

> 
> I can't quite work out how to get XFS to put the logs on another device
> or volume. A few questions:
> 
> 1) How does one setup the other device?
>  - does it need a separate partition
>  - or...?

Yes, the external log needs it's own partition, on any disk.  I suppose
a whole disk might work, but that would be a horrible waste of space.  :)

> 2) What would a mkfs.xfs look like for this situation?
>  - could one alter an existing partition to use an external log

Well, from the man page.... ;-)

       The metadata log can be placed on another device to reduce
       the number of disk seeks.  To create a filesystem  on  the
       first  partition on the first SCSI disk with a 10000 block
       log located on the first  partition  on  the  second  SCSI
       disk, use:

            mkfs.xfs -l logdev=/dev/sdb1,size=10000b /dev/sda1

It's technically possible to alter an existing internal-log fs to use
an external log, but it's neither automatic nor supported.

> 3) What would happen if the other device went down but the main device
> didn't?

Your next log write would fail, and the filesystem would shut down.  You'd
also have a slightly inconsistent fs, but in general you could recover
from it.

-Eric
> 
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> 
> 


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