[linux-lvm] ext3 on an logical volume - snapshot using how?

[linux-lvm] ext3 on an logical volume - snapshot using how?

[Ph. Marek]

Hi everybody!

I'm using LVM and ext3 and am very satisfied with it.


But now I have the following problem:
I have a filesystem on a LV which is in use -
files are created, modified and so on.
To do a backup I'd like to create a snapshot
of this volume which gets backup'd  and then dropped.

	 # lvcreate -s -L 20M -n snapshot /dev/vg/data
	lvcreate -- WARNING: the snapshot will be automatically disabled once it gets full
	lvcreate -- INFO: using default snapshot chunk size of 64.00 KB for "/dev/vg/snapshot"
	lvcreate -- doing automatic backup of "vg"
	lvcreate -- logical volume "/dev/vg/snapshot" successfully created

So far, so good.
Now I want to mount that filesystem - after all, it's 
possible several GB of which only parts are used.

(statements mixed with output in /var/log/messages ">")

	 # mount /dev/vg/snapshot /mnt/tmp/
	mount: block device /dev/vg/snapshot is write-protected, mounting read-only
	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
	       or too many mounted file systems
	> EXT2-fs: lvm(58,12): couldn't mount because of unsupported optional features (4).

	 # mount /dev/vg/snapshot /mnt/tmp/ -t ext3
	mount: block device /dev/vg/snapshot is write-protected, mounting read-only
	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
	       or too many mounted file systems
	> EXT3-fs: INFO: recovery required on readonly filesystem.
	> EXT3-fs: write access unavailable, cannot proceed.

So looking in the kernel sources I find some mount-options ...

	 # mount /dev/vg/snapshot /mnt/tmp/ -t ext3 -o ro,errors=remount-ro
	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
	       or too many mounted file systems
	> EXT3-fs: INFO: recovery required on readonly filesystem.
	> EXT3-fs: write access unavailable, cannot proceed.

	 # mount /dev/vg/snapshot /mnt/tmp/ -t ext3 -o ro,errors=remount-ro,noload
	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
	       or too many mounted file systems
	> ext3: No journal on filesystem on lvm(58,12) 

If the snapshot wasn't ro I'd do a tune2fs or e2fsck or something.

So can somebody please drop me a hint?
Is that not possible?


Thanks in advance!!


Regards,

Phil

[linux-lvm] RE: ext3 on an logical volume - snapshot using how?

[Rechenberg, Andrew]

I believe you need the VFS-lock patch applied to your kernel to be able to do snapshots on a journaling filesystem (LVM/ext3 gurus correct me if I am incorrect).  Patches for various kernels are in PATCHES directory in the LVM source.  Read the README file in the PATCHES directory for more info.

I have applied this patch to clean 2.4.18 source, compiled and running on RedHat 7.2 (which doesn't include LVM in the distro), and have successfully created snapshots of logical volumes.

Hope this helps.

Regards,
Andy.


Andrew Rechenberg
Network Team, Sherman Financial Group


-----Original Message-----
From: Ph. Marek [mailto:marek@bmlv.gv.at]
Sent: Monday, April 08, 2002 9:53 AM
To: ext3-users@redhat.com; linux-lvm@sistina.com
Subject: ext3 on an logical volume - snapshot using how?


Hi everybody!

I'm using LVM and ext3 and am very satisfied with it.


But now I have the following problem:
I have a filesystem on a LV which is in use -
files are created, modified and so on.
To do a backup I'd like to create a snapshot
of this volume which gets backup'd  and then dropped.

	 # lvcreate -s -L 20M -n snapshot /dev/vg/data
	lvcreate -- WARNING: the snapshot will be automatically disabled once it gets full
	lvcreate -- INFO: using default snapshot chunk size of 64.00 KB for "/dev/vg/snapshot"
	lvcreate -- doing automatic backup of "vg"
	lvcreate -- logical volume "/dev/vg/snapshot" successfully created

So far, so good.
Now I want to mount that filesystem - after all, it's 
possible several GB of which only parts are used.

(statements mixed with output in /var/log/messages ">")

	 # mount /dev/vg/snapshot /mnt/tmp/
	mount: block device /dev/vg/snapshot is write-protected, mounting read-only
	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
	       or too many mounted file systems
	> EXT2-fs: lvm(58,12): couldn't mount because of unsupported optional features (4).

	 # mount /dev/vg/snapshot /mnt/tmp/ -t ext3
	mount: block device /dev/vg/snapshot is write-protected, mounting read-only
	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
	       or too many mounted file systems
	> EXT3-fs: INFO: recovery required on readonly filesystem.
	> EXT3-fs: write access unavailable, cannot proceed.

So looking in the kernel sources I find some mount-options ...

	 # mount /dev/vg/snapshot /mnt/tmp/ -t ext3 -o ro,errors=remount-ro
	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
	       or too many mounted file systems
	> EXT3-fs: INFO: recovery required on readonly filesystem.
	> EXT3-fs: write access unavailable, cannot proceed.

	 # mount /dev/vg/snapshot /mnt/tmp/ -t ext3 -o ro,errors=remount-ro,noload
	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
	       or too many mounted file systems
	> ext3: No journal on filesystem on lvm(58,12) 

If the snapshot wasn't ro I'd do a tune2fs or e2fsck or something.

So can somebody please drop me a hint?
Is that not possible?


Thanks in advance!!


Regards,

Phil



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[linux-lvm] Re: ext3 on an logical volume - snapshot using how?

[Stephen C. Tweedie]

Hi,

On Mon, Apr 08, 2002 at 03:53:17PM +0200, Ph. Marek wrote:
 
> I'm using LVM and ext3 and am very satisfied with it.
> 
> But now I have the following problem:
> I have a filesystem on a LV which is in use -
> files are created, modified and so on.
> To do a backup I'd like to create a snapshot
> of this volume which gets backup'd  and then dropped.

> 	mount: wrong fs type, bad option, bad superblock on /dev/vg/snapshot,
> 	       or too many mounted file systems
> 	> EXT3-fs: INFO: recovery required on readonly filesystem.
> 	> EXT3-fs: write access unavailable, cannot proceed.

> If the snapshot wasn't ro I'd do a tune2fs or e2fsck or something.

There is a "VFS-lock" patch distributed with the LVM sources, which
adds code to LVM to tell filesystems to quiesce themselves for a
snapshot.  This results in a filesystem which can be mounted safely
without recovery.

Ext3 already supports this functionality, but the LVM code in the main
kernel does not have the code to call it.  The VFS-lock patch adds
that code.

Cheers,
 Stephen