From: Eric Sandeen <sandeen@sandeen.net>
To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com, aurfalien <aurfalien@gmail.com>
Subject: Re: LVM + XFS + external log + snapshots
Date: Sun, 23 Jun 2013 18:24:39 -0500 [thread overview]
Message-ID: <51C783B7.2040502@sandeen.net> (raw)
In-Reply-To: <20130623225546.GB29376@dastard>
On 6/23/13 5:55 PM, Dave Chinner wrote:
> On Fri, Jun 21, 2013 at 10:30:31PM -0700, aurfalien wrote:
>> Hi all,
>>
>> So I have an XFS file system within LVM which has an external log.
>>
>> My mount option in FSTAB is;
>>
>> /dev/vg_spock_data/lv_data /data xfs logdev=/dev/sdc1,nobarrier,logbufs=8,noatime,nodiratime 1 1
>>
>> All is well no issues and very fast.
>>
>> Now I'd like to snapshot this bad boy and then run rsnapshot to create a few days backup.
>
> You need to snapshot the log device as well.
>
> But that is problematic in that you need to snapshot it at the same
> time you snapshot the data volume. Hence yo'd have to do:
>
> # xfs_freeze -f <filesystem>
> # <snapshot data volume>
> # <snapshot log volume>
> # xfs_freeze -u <filesystem>
>
> And now you can mount the snapshot with:
>
> # mount /dev/vg_spock_data/datasnapshot /snapshot -o nouuid,ro,logdev=/dev/vg_spock_log/logsnapshot
>
> If you can't snapshot the log device, then you can't snapshot the
> filesystem. Yet another reason for using internal logs...
Hm, given that freezing the fs makes the log (almost) completely clean, I wonder
if he could mount with /dev/zero (or a loopback 0-filled file) to get at the snapshot,
especially since it's being mounted RO.
Should be safe & consistent, no?
i.e.
truncate --size=2g logfile (or however big it needs to be)
losetup /dev/loop0 logfile
mount /dev/vg_anette_data/datasnapshot /snapshot -o logdev=/dev/loop0,nouuid,ro
-Eric
> Cheers,
>
> Dave.
>
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next prev parent reply other threads:[~2013-06-23 23:24 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-22 5:30 LVM + XFS + external log + snapshots aurfalien
2013-06-22 7:58 ` Stan Hoeppner
2013-06-22 21:13 ` aurfalien
2013-06-23 22:55 ` Dave Chinner
2013-06-23 23:24 ` Eric Sandeen [this message]
2013-06-23 23:39 ` Dave Chinner
2013-06-24 0:33 ` aurfalien
2013-06-24 0:44 ` aurfalien
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