Description of problem:

here: http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html-single/Logical_Volume_Manager_Administration/index.html#mirrorrecover
In chapter 6.3 it states an example where a write to the mirror after one leg has failed causes LVM to detect the error and remove the faulty mirror part from volume, turning it to a linear device (mirrorrecover, chapter 6.3). While it is true that LVM removes the broken leg, the writing to the lv in the example corrupts the filesystem:



In this example, the primary leg of the mirror /dev/sda1 fails. Any write activity to the mirrored volume causes LVM to detect the failed mirror. When this occurs, LVM converts the mirror into a single linear volume. In this case, to trigger the conversion, we execute a dd command

[root@link-08 ~]# dd if=/dev/zero of=/dev/vg/groupfs count=10
10+0 records in
10+0 records out

You can use the lvs command to verify that the device is now a linear device. Because of the failed disk, I/O errors occur.

[root@link-08 ~]# lvs -a -o +devices
  /dev/sda1: read failed after 0 of 2048 at 0: Input/output error
  /dev/sda2: read failed after 0 of 2048 at 0: Input/output error
  LV      VG   Attr   LSize   Origin Snap%  Move Log Copy%  Devices
  groupfs vg   -wi-a- 752.00M                               /dev/sdb1(0)


At this point you should still be able to use the logical volume, but there will be no mirror redundancy. 



Version-Release number of selected component (if applicable):

Book identifier: Logical_Volume_Manager_Administration(EN)-5 (2010-12-23T15:20)


How reproducible:
100%


Steps to Reproduce:

[root@g0rion ~]# lvcreate -L 1G vg_skeleton -n test
  Logical volume "test" created
[root@g0rion ~]# mkfs.ext4 /dev/vg_skeleton/test 
mke2fs 1.41.14 (22-Dec-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
65536 inodes, 262144 blocks
13107 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=268435456
8 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376

Writing inode tables: done                            
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 22 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
[root@g0rion ~]# mount /dev/vg_skeleton/test /mnt/
[root@g0rion ~]# umount /mnt/
[root@g0rion ~]# dd if=/dev/zero of=/dev/vg_skeleton/test count=10
10+0 records in
10+0 records out
5120 bytes (5.1 kB) copied, 0.0164429 s, 311 kB/s
[root@g0rion ~]# mount /dev/vg_skeleton/test /mnt/
mount: you must specify the filesystem type



Actual results:

[root@g0rion ~]# mount /dev/vg_skeleton/test /mnt/
mount: you must specify the filesystem type

Expected results:


At this point you should still be able to use the logical volume, but there will be no mirror redundancy.