LVM mirroring

Mirror setup

  1. Create pv.
# pvcreate /dev/sd[bc]
  Writing physical volume data to disk "/dev/sdb"
  Physical volume "/dev/sdb" successfully created
  Writing physical volume data to disk "/dev/sdc"
  Physical volume "/dev/sdc" successfully created
  1. Create vg.
# vgcreate -s 4m vgmirror /dev/sd[bc]
  Volume group "vgmirror" successfully created
  1. Create mirrored lv.
# lvcreate -L 4g -m 1 -n mirror vgmirror
  Logical volume "mirror" created
  1. Monitor mirror silvering.
# lvs vgmirror
  LV     VG       Attr     LSize [[snip]]  Move Log         Copy%  Convert
  mirror vgmirror mwi-a-m- 4.00g                mirror_mlog   7.23
# lvs vgmirror
  LV     VG       Attr     LSize [[snip]]  Move Log         Copy%  Convert
  mirror vgmirror mwi-a-m- 4.00g                mirror_mlog  27.15
# lvs vgmirror
  LV     VG       Attr     LSize [[snip]]  Move Log         Copy%  Convert
  mirror vgmirror mwi-a-m- 4.00g                mirror_mlog 100.00
  1. Create filesystem and mount
# mkfs.ext4 /dev/vgmirror/mirror
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
[[snip]]
This filesystem will be automatically checked every 33 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
# mkdir -p -m 755 /mnt/mirror
# mount /dev/vgmirror/mirror /mnt/mirror
# echo "This is a test of the emergency broadcasting system." > /mnt/mirror/README
# md5sum /mnt/mirror/README
9a75a8122c57b3ae0e4831d30b744593  /mnt/mirror/README

Splitting the mirror and volume group

  1. W/filesystem still mounted, split the mirror:
# lvconvert --splitmirrors 1 --name copy vgmirror/mirror
  Logical volume mirror converted.
# lvs vgmirror -o +devices
  LV     VG       Attr     LSize [[snip]]  Convert Devices
  copy   vgmirror -wi-a--- 4.00g                   /dev/sdc(0)
  mirror vgmirror -wi-ao-- 4.00g                   /dev/sdb(0)
  1. Split the volume group:
# lvchange -a n vgmirror/copy
# vgsplit vgmirror vgcopy /dev/sdc
  New volume group "vgcopy" successfully split from "vgmirror"
# vgs -o +devices | grep -v vg00
  VG       #PV #LV #SN Attr   VSize  VFree Devices
  vgcopy     1   1   0 wz--n- 10.00g 6.00g /dev/sdc(0)
  vgmirror   1   1   0 wz--n- 10.00g 6.00g /dev/sdb(0)
# lvs -o +devices | grep -v vg00
  LV     VG       Attr     LSize  [[snip]]  Convert Devices
  copy   vgcopy   -wi-----  4.00g                   /dev/sdc(0)
  mirror vgmirror -wi-ao--  4.00g                   /dev/sdb(0)
  1. Activate, and mount the split vg/lv
# lvchange -a y vgcopy/copy
# mkdir -p -m 755 /mnt/mirror1
# mount /dev/vgcopy/copy /mnt/mirror1
# md5sum /mnt/mirror/README /mnt/mirror1/README
9a75a8122c57b3ae0e4831d30b744593  /mnt/mirror/README
9a75a8122c57b3ae0e4831d30b744593  /mnt/mirror1/README

Resilver split mirrors and volume groups

  1. Unmount/delete split logical volume. Source lv stays mounted.
# umount /mnt/mirror1
# lvremove -f vgcopy/copy
  Logical volume "copy" successfully removed
# lvs vgmirror vgcopy -o +devices
  LV     VG       Attr     LSize [[split]]  Convert Devices
  mirror vgmirror -wi-ao-- 4.00g                    /dev/sdb(0)
  1. Merge split volume groups:
# vgmerge vgmirror vgcopy
  Volume group "vgcopy" successfully merged into "vgmirror"
  1. Remirror logical volume:
# lvconvert -m 1 vgmirror/mirror
  vgmirror/mirror: Converted: 0.0%
  vgmirror/mirror: Converted: 4.3%
  [[snip]]
  vgmirror/mirror: Converted: 99.3%
  vgmirror/mirror: Converted: 100.0%
# vgs
  VG       #PV #LV #SN Attr   VSize  VFree
  vg00       1   2   0 wz--n- 19.51g     0
  vgmirror   2   1   0 wz--n- 19.99g 11.99g
# lvs
  LV     VG       Attr     LSize  [[snip]]  Move Log         Copy%  Convert
  root   vg00     -wi-ao-- 17.54g
  swap   vg00     -wi-ao--  1.97g
  mirror vgmirror mwi-aom-  4.00g               mirror_mlog 100.00

Error conditions: simulated disk failure

  1. Shutdown guest, delete one of the disks, and restart guest
# virsh destroy guest
Domain guest destroyed
# virsh domblklist guest
Target     Source
------------------------------------------------
hda        /var/lib/libvirt/images/guest.img
hdb        /var/lib/libvirt/images/guest-1.img
hdc        /var/lib/libvirt/images/guest-2.img
# virsh detach-disk guest hdb --persistent
Disk detached successfully
# virsh domblklist guest
Target     Source
------------------------------------------------
hda        /var/lib/libvirt/images/guest.img
hdc        /var/lib/libvirt/images/guest-2.img
# virsh start guest
Domain guest started
  1. Check for mounted filesystem, errors:
# h
guest
# mount | grep mirror
# mount /dev/vgmirror/mirror /mnt/mirror
mount: you must specify the filesystem type
# lvdisplay /dev/vgmirror/mirror
  **Couldn't find device with uuid WupKj6-4auC-H3Qg-xdK2-Fb8g-ttKJ-XMQEEt.**
  --- Logical volume ---
  LV Path                /dev/vgmirror/mirror
  LV Name                mirror
  VG Name                vgmirror
  LV UUID                TXwTkn-umnN-4Xh3-OuAE-SDJn-0Mh4-ELqIeT
  LV Write Access        read/write
  LV Creation host, time guest, 2013-03-24 08:57:35 -0500
  **LV Status              NOT available**
  LV Size                4.00 GiB
  Current LE             1024
  Mirrored volumes       2
  **Segments               1**
  Allocation             inherit
  Read ahead sectors     auto
# vgdisplay vgmirror
  Couldn't find device with uuid DzqgRx-kwyZ-kp6O-xSSt-MO3m-sDiq-v9baRp.
  --- Volume group ---
  VG Name               vgmirror
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  29
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               0
  Max PV                0
  **Cur PV                2**
  **Act PV                1**
  VG Size               19.99 GiB
  PE Size               4.00 MiB
  Total PE              5118
  Alloc PE / Size       2049 / 8.00 GiB
  Free  PE / Size       3069 / 11.99 GiB
  VG UUID               0sof6K-R7ub-8mtG-3jYJ-xXzP-RYCD-6nDRPS
# lvchange -a y vgmirror/mirror
  Couldn't find device with uuid WupKj6-4auC-H3Qg-xdK2-Fb8g-ttKJ-XMQEEt.
  Refusing activation of partial LV mirror. Use --partial to override.
# lvchange -a y --partial vgmirror/mirror
  Partial mode. Incomplete logical volumes will be processed.
  Couldn't find device with uuid WupKj6-4auC-H3Qg-xdK2-Fb8g-ttKJ-XMQEEt.
# mount /dev/vgmirror/mirror /mnt/mirror
# mount | grep mirror
/dev/mapper/vgmirror-mirror on /mnt/mirror type ext4 (rw)
# pvs
  **Couldn't find device with uuid WupKj6-4auC-H3Qg-xdK2-Fb8g-ttKJ-XMQEEt.**
  PV             VG       Fmt  Attr PSize  PFree
  /dev/sda2      vg00     lvm2 a--  19.51g     0
  /dev/sdb       vgmirror lvm2 a--  10.00g  6.00g
  **unknown device vgmirror lvm2 a-m  10.00g 10.00g**
  1. Fix the volume group:
# vgreduce --removemissing --force vgmirror
  Couldn't find device with uuid WupKj6-4auC-H3Qg-xdK2-Fb8g-ttKJ-XMQEEt.
  Wrote out consistent volume group vgmirror
# vgdisplay vgmirror
  --- Volume group ---
  VG Name               vgmirror
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  26
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               1
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               10.00 GiB
  PE Size               4.00 MiB
  Total PE              2559
  Alloc PE / Size       1024 / 4.00 GiB
  Free  PE / Size       1535 / 6.00 GiB
  VG UUID               0sof6K-R7ub-8mtG-3jYJ-xXzP-RYCD-6nDRPS
# lvdisplay /dev/vgmirror/mirror
  --- Logical volume ---
  LV Path                /dev/vgmirror/mirror
  LV Name                mirror
  VG Name                vgmirror
  LV UUID                TXwTkn-umnN-4Xh3-OuAE-SDJn-0Mh4-ELqIeT
  LV Write Access        read/write
  LV Creation host, time guest, 2013-03-24 08:57:35 -0500
  LV Status              available
  # open                 1
  LV Size                4.00 GiB
  Current LE             1024
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:6
  1. Replace disk, remirror logical volume:
# virsh destroy guest
Domain guest destroyed

# virsh domblklist guest
Target     Source
------------------------------------------------
hda        /var/lib/libvirt/images/guest.img
hdc        /var/lib/libvirt/images/guest-2.img

# virsh vol-create-as default guest-3.img 10g
Vol guest-3.img created

# virsh attach-disk guest /var/lib/libvirt/images/guest-3.img hdd --persistent
Disk attached successfully

# virsh domblklist guest
Target     Source
------------------------------------------------
hda        /var/lib/libvirt/images/guest.img
hdc        /var/lib/libvirt/images/guest-2.img
hdd        /var/lib/libvirt/images/guest-3.img

# virsh start guest
Domain guest started
# ssh guest
Last login: Sun Mar 24 10:13:12 2013 from 192.168.122.1
# grep sd /proc/partitions | sort -k 4
   8        0   20971520 sda
   8        1     512000 sda1
   8        2   20458496 sda2
   8       16   10485760 sdb
   8       32   10485760 sdc
# pvs
  PV         VG       Fmt  Attr PSize  PFree
  /dev/sda2  vg00     lvm2 a--  19.51g    0
  /dev/sdb   vgmirror lvm2 a--  10.00g 6.00g
# pvcreate /dev/sdc
  Writing physical volume data to disk "/dev/sdc"
  Physical volume "/dev/sdc" successfully created
# vgextend vgmirror /dev/sdc
  Volume group "vgmirror" successfully extended
# lvconvert -m 1 vgmirror/mirror
  vgmirror/mirror: Converted: 0.0%
  vgmirror/mirror: Converted: 2.2%
  vgmirror/mirror: Converted: 4.3%
  [[snip]]
  vgmirror/mirror: Converted: 96.2%
  vgmirror/mirror: Converted: 98.3%
  vgmirror/mirror: Converted: 100.0%
# lvdisplay vgmirror/mirror | grep -i mirrored
  Mirrored volumes       2
# vgdisplay vgmirror | grep -i pv
  Max PV                0
  Cur PV                2
  Act PV                2