LVM Disk Mirroring for REL5

i checked it out with my desktop and a usb stick it works pretty god :)

1 setup the devices

pvcreate /dev/sda1
pvcreate /dev/sdb1
vgcreate VG0 /dev/sda1 /dev/sdb1
lvcreate -L 1024M -m1 --corelog -n mirror1 VG0
mkfs.ext3 /dev/VG0/mirror1
mkdir /mnt/disk
mount /dev/VG0/mirror1 /mnt/disk
df -h

2 lets see how it works

lvs -a -o +devices
  LV                 VG   Attr   LSize  Origin Snap%  Move Log Copy%  Convert Devices                                                       
  mirror1            VG0  mwi-ao  1.00G                         50.00         mirror1_mimage_0(0),mirror1_mimage_1(0)
  [mirror1_mimage_0] VG0  Iwi-ao  1.00G                                       /dev/sda1(3544)                        
  [mirror1_mimage_1] VG0  Iwi-ao  1.00G                                       /dev/sdb1(0)                           

cp /home/chris/private/vid/Kiss_Kiss_Bang_Bang.avi /mnt/disk/
md5sum /mnt/disk/Kiss_Kiss_Bang_Bang.avi

3 destroy the mirror

be sure its sync

lvs -a -o +devices
  LV                 VG   Attr   LSize  Origin Snap%  Move Log Copy%  Convert Devices                                
  mirror1            VG0  mwi-ao  1.00G                        100.00         mirror1_mimage_0(0),mirror1_mimage_1(0)
  [mirror1_mimage_0] VG0  iwi-ao  1.00G                                       /dev/sda1(3544)                        
  [mirror1_mimage_1] VG0  iwi-ao  1.00G                                       /dev/sdb1(0)                           

pull out one disk (sdb1) and check what happend :)

vlc /mnt/disk/Kiss_Kiss_Bang_Bang.avi

oh boy, this is a hard job

lvs -a -o +devices
  LV        VG   Attr   LSize  Origin Snap%  Move Log Copy%  Convert Devices
  mirror1   VG0  -wi-ao  1.00G                                       /dev/sda1(3544)

now. the mirror is gone

4 repair the mirror

put the disk back into the server

pvs
  WARNING: Volume Group VG0 is not consistent
  PV         VG   Fmt  Attr PSize   PFree 
  /dev/sda1  VG0  lvm2 a-   148.91G 40.22G

recreate the pv

pvcreate /dev/sdb1
  WARNING: Volume group VG0 is not consistent
  Physical volume "/dev/sdb1" successfully created

add it to the vg again

pvs
  PV         VG   Fmt  Attr PSize   PFree 
  /dev/sda1  VG0  lvm2 a-   148.91G 40.22G
  /dev/sdb1       lvm2 --     1.91G  1.91G

vgextend VG0 /dev/sdb1
  Volume group "VG0" successfully extended

pvs
  PV         VG   Fmt  Attr PSize   PFree 
  /dev/sda1  VG0  lvm2 a-   148.91G 40.22G
  /dev/sdb1  VG0  lvm2 a-     1.91G  1.91G

lvconvert -m1 --corelog /dev/VG0/mirror1 
  /dev/VG0/mirror1: Converted: 3.1%
  /dev/VG0/mirror1: Converted: 6.2%
  ...

thats all, its a nice thing
it worked fine, and the data are save

here also some nice logs

Dec  2 14:19:17 lompetier lvm[22839]: VG0-mirror1 is now in-sync 
Dec  2 14:21:35 lompetier kernel: usb 1-3: USB disconnect, address 7
Dec  2 14:21:42 lompetier kernel: scsi 7:0:0:0: rejecting I/O to dead device
Dec  2 14:22:17 lompetier last message repeated 20 times
Dec  2 14:22:17 lompetier kernel: device-mapper: raid1: A read failure occurred on a mirror device.
Dec  2 14:22:17 lompetier kernel: device-mapper: raid1: Trying different device.
Dec  2 14:22:18 lompetier kernel: scsi 7:0:0:0: rejecting I/O to dead device
Dec  2 14:22:18 lompetier lvm[22839]: Mirror device, 253:11, has failed. 
Dec  2 14:22:18 lompetier lvm[22839]: Device failure in VG0-mirror1 
Dec  2 14:22:18 lompetier lvm[22839]: WARNING: dev_open(/etc/lvm/lvm.conf) called while suspended
Dec  2 14:22:25 lompetier kernel: scsi 7:0:0:0: rejecting I/O to dead device
Dec  2 14:22:25 lompetier last message repeated 3 times
Dec  2 14:22:25 lompetier lvm[22839]: WARNING: dev_open(/dev/mapper/VG0-mirror1_mimage_1) called while suspended
Dec  2 14:22:25 lompetier kernel: scsi 7:0:0:0: rejecting I/O to dead device
Dec  2 14:22:26 lompetier lvm[22839]: WARNING: Bad device removed from mirror volume, VG0/mirror1
Dec  2 14:22:26 lompetier lvm[22839]: WARNING: Mirror volume, VG0/mirror1 converted to linear due to device failure.
Dec  2 14:22:28 lompetier lvm[22839]: WARNING: dev_open(/etc/lvm/lvm.conf) called while suspended
Dec  2 14:22:30 lompetier lvm[22839]: No longer monitoring mirror device VG0-mirror1 for events 

5 Links

how mirroring works
how to configure it