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File-system uuid on LVM snapshot

linux-lvm Rajesh Joseph 2 participants 4 messages Jun 5, 2014 1 message not in the archive

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Rajesh Joseph

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#1 lore raw

Hi all,

Origin volume and snapshot volume share the same file-system UUID. So after the snapshot we fix the uuid by running xfs_admin or tune2fs. Do you have any recommendation or best practice in this regard?

Thanks & Regards,
Rajesh

#2 lore raw

Dne 5.6.2014 10:26, Rajesh Joseph napsal(a):

Quoted 5 lines

Hi all,

Origin volume and snapshot volume share the same file-system UUID. So after the snapshot we fix the uuid by running xfs_admin or tune2fs. Do you have any recommendation or best practice in this regard?

With thin pools and thin volumes - snapshot of thin volume is now created 'inactive' and it's skipped from default activation (you could always override skip with -K i.e. : lvchange -ay -K vg/mythinsnap)

So with thins you should mostly have only a single volume active with the FS UUID. If you happen to have multiple volumes active and you need to mount xfs filesystem - use 'nouuid' (and eventually norecovery for read-only activated snapshots) mount options.

For old-snapshosts - all volumes need to be available/active - so you need to use 'nouuid' option always.

I don't see much point in changing FS UUID on your snapshot - unless of course you plan to use snapshots as different volumes with just a 'single' starting point (i.e. preinstalled tree of files)

Regards

Zdenek

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#3 lore raw

Thanks Zdenek for the quick reply.

We are using thin volumes and thin snapshot, but we need all or most snapshots active. Therefore we are enabling the snapshot by-default. As you suggested we can have a workaround to mount those snapshot volumes by using 'nouuid' option.
But the problem is in most of our use case the origin volume is mounted using the /etc/fstab. And here the mount entry is made using UUID. So in some cases instead of Origin volume the snapshot volume get mounted.

Thanks & Regards,
Rajesh

----- Original Message -----

Quoted 42 lines

From: "Zdenek Kabelac" <[email protected]>
To: [email protected]
Sent: Thursday, June 5, 2014 2:49:51 PM
Subject: Re: [linux-lvm] File-system uuid on LVM snapshot

Dne 5.6.2014 10:26, Rajesh Joseph napsal(a):

Quoted 6 lines

Hi all,

Origin volume and snapshot volume share the same file-system UUID. So after the snapshot we fix the uuid by running xfs_admin or tune2fs. Do you have any recommendation or best practice in this regard?

With thin pools and thin volumes - snapshot of thin volume is now created 'inactive' and it's skipped from default activation (you could always override skip with -K i.e. : lvchange -ay -K vg/mythinsnap)

So with thins you should mostly have only a single volume active with the FS UUID. If you happen to have multiple volumes active and you need to mount xfs
filesystem - use 'nouuid' (and eventually norecovery for read-only activated snapshots) mount options.

For old-snapshosts - all volumes need to be available/active - so you need to use 'nouuid' option always.

I don't see much point in changing FS UUID on your snapshot - unless of course you plan to use snapshots as different volumes with just a 'single' starting point (i.e. preinstalled tree of files)

Regards

Zdenek

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#4 lore raw

Dne 5.6.2014 11:29, Rajesh Joseph napsal(a):

Quoted 6 lines

Thanks Zdenek for the quick reply.

We are using thin volumes and thin snapshot, but we need all or most snapshots active. Therefore we are enabling the snapshot by-default. As you suggested we can have a workaround to mount those snapshot volumes by using 'nouuid' option.
But the problem is in most of our use case the origin volume is mounted using the /etc/fstab. And here the mount entry is made using UUID. So in some cases instead of Origin volume the snapshot volume get mounted.

So this rather looks like you are not using 'snapshot' as snapshot but rather as a quick COW device clone - where you obviously need to change identifiers, since they are used later independently. (something like we do with 'vgimportclone' where we duplicate VG)

Maybe it might be worth to think about fsadm extension to support filesystem cloning as a built-in feature which would handle change if fs UUID across different filesystems...

Regards

Zdenek