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5.4.16.9. Replacing a RAID device
RAID is not like traditional LVM mirroring. LVM mirroring required failed devices to be removed or the mirrored logical volume would hang. RAID arrays can keep on running with failed devices. In fact, for RAID types other than RAID1, removing a device would mean converting to a lower level RAID (for example, from RAID6 to RAID5, or from RAID4 or RAID5 to RAID0). Therefore, rather than removing a failed device unconditionally and potentially allocating a replacement, LVM allows you to replace a device in a RAID volume in a one-step solution by using the
--replace argument of the lvconvert command.
The format for the
lvconvert --replace is as follows.
lvconvert --replace dev_to_remove vg/lv [possible_replacements]
The following example creates a RAID1 logical volume and then replaces a device in that volume.
# lvcreate --type raid1 -m2 -L 1G -n my_lv my_vg
Logical volume "my_lv" created
# lvs -a -o name,copy_percent,devices my_vg
LV Copy% Devices
my_lv 100.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0] /dev/sdb1(1)
[my_lv_rimage_1] /dev/sdb2(1)
[my_lv_rimage_2] /dev/sdc1(1)
[my_lv_rmeta_0] /dev/sdb1(0)
[my_lv_rmeta_1] /dev/sdb2(0)
[my_lv_rmeta_2] /dev/sdc1(0)
# lvconvert --replace /dev/sdb2 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV Copy% Devices
my_lv 37.50 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0] /dev/sdb1(1)
[my_lv_rimage_1] /dev/sdc2(1)
[my_lv_rimage_2] /dev/sdc1(1)
[my_lv_rmeta_0] /dev/sdb1(0)
[my_lv_rmeta_1] /dev/sdc2(0)
[my_lv_rmeta_2] /dev/sdc1(0)
The following example creates a RAID1 logical volume and then replaces a device in that volume, specifying which physical volume to use for the replacement.
# lvcreate --type raid1 -m1 -L 100 -n my_lv my_vg
Logical volume "my_lv" created
# lvs -a -o name,copy_percent,devices my_vg
LV Copy% Devices
my_lv 100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0] /dev/sda1(1)
[my_lv_rimage_1] /dev/sdb1(1)
[my_lv_rmeta_0] /dev/sda1(0)
[my_lv_rmeta_1] /dev/sdb1(0)
# pvs
PV VG Fmt Attr PSize PFree
/dev/sda1 my_vg lvm2 a-- 1020.00m 916.00m
/dev/sdb1 my_vg lvm2 a-- 1020.00m 916.00m
/dev/sdc1 my_vg lvm2 a-- 1020.00m 1020.00m
/dev/sdd1 my_vg lvm2 a-- 1020.00m 1020.00m
# lvconvert --replace /dev/sdb1 my_vg/my_lv /dev/sdd1
# lvs -a -o name,copy_percent,devices my_vg
LV Copy% Devices
my_lv 28.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0] /dev/sda1(1)
[my_lv_rimage_1] /dev/sdd1(1)
[my_lv_rmeta_0] /dev/sda1(0)
[my_lv_rmeta_1] /dev/sdd1(0)
You can replace more than one RAID device at a time by specifying multiple
replace arguments, as in the following example.
# lvcreate --type raid1 -m 2 -L 100 -n my_lv my_vg
Logical volume "my_lv" created
# lvs -a -o name,copy_percent,devices my_vg
LV Copy% Devices
my_lv 100.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0] /dev/sda1(1)
[my_lv_rimage_1] /dev/sdb1(1)
[my_lv_rimage_2] /dev/sdc1(1)
[my_lv_rmeta_0] /dev/sda1(0)
[my_lv_rmeta_1] /dev/sdb1(0)
[my_lv_rmeta_2] /dev/sdc1(0)
# lvconvert --replace /dev/sdb1 --replace /dev/sdc1 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV Copy% Devices
my_lv 60.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0] /dev/sda1(1)
[my_lv_rimage_1] /dev/sdd1(1)
[my_lv_rimage_2] /dev/sde1(1)
[my_lv_rmeta_0] /dev/sda1(0)
[my_lv_rmeta_1] /dev/sdd1(0)
[my_lv_rmeta_2] /dev/sde1(0)
Note
When you specify a replacement drive using the
lvconvert --replace command, the replacement drives should never be allocated from extra space on drives already used in the array. For example, lv_rimage_0 and lv_rimage_1 should not be located on the same physical volume.
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