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Re: [linux-lvm] lvm2 2.02.105 breaks snapshots



Dne 4.2.2014 09:55, Christian Hesse napsal(a):
Christian Hesse <list eworm de> on Thu, 2014/01/23 14:27:
Hello everybody,

looks like lvm2 2.02.105 breaks snapshots. This is my block device tree:

NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda                   8:0    0   477G  0 disk
|-sda1                8:1    0   767M  0 part
| `-vg0-boot        254:0    0    64M  0 lvm   /boot
|-sda2                8:2    0 444,2G  0 part
| `-cvg             254:3    0 444,2G  0 crypt
|   |-cvg-root      254:4    0    40G  0 lvm   /
|   |-cvg-swap      254:5    0     4G  0 lvm   [SWAP]
|   |-cvg-log       254:6    0     1G  0 lvm   /var/log
|   `-cvg-home      254:8    0   320G  0 lvm   /home
|-sda3                8:3    0    32G  0 part
`-sda128            259:0    0     1M  0 part

Creating a snapshot succeeds, but it is broken and can not be mounted:

# lvcreate -s -pr -l50%free -n snap-home cvg/home
   Logical volume "snap-home" created
# mount /dev/cvg/snap-home /mnt/tmp
mount: /dev/mapper/cvg-snap--home is write-protected, mounting read-only
mount: wrong fs type, bad option, bad superblock on
/dev/mapper/cvg-snap--home, missing codepage or helper program, or other
error

Syslog has a lot of these messages:

[ 4823.002220] EXT4-fs (dm-7): ext4_check_descriptors: Checksum for group
256 failed (43470!=57954)

Downgrading to lvm2 2.02.104 fixes the problem:

# lvcreate -s -pr -l50%free -n snap-home
cvg/home Logical volume "snap-home" created
# mount /dev/cvg/snap-home /mnt/tmp
mount: /dev/mapper/cvg-snap--home is write-protected, mounting read-only

This is an Arch Linux system with Linux 3.12.8.

Hello everybody,

did anybody notice my mail? This is a real regression for me and I would like
to get this sorted. I will help with whatever is needed to find the problem.



Ok -  could you test this:

Create an lv  -  ('lvcreate -Lsmallsize  vg'
mount this lv somewhere
modify this filesystem (via dd)

'fsfreeze --freeze  mountpoint'

now  - copy whole frozen device somewhere (via dd)

'fsfreeze --unfreeze mountpoint'

umount mountpoint

losetup -r  /dev/loop_free_number    frozen_copy_of_device

and now - try to mount your  read-only loop device copy.

Does it work for you ?

I've been testing this - and it seem fsfreeze API in kernel is not working properly and you need to reply journal.

Then try to repeat the same with 3.10 kernel and 3.4 kernel.

So far I'm not convinced lvm2 version has anything to do with this problem

For 3.10  ext4 seems to work, but xfs is broken.

Regards

Zdenek




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