RE adding new disk to mirrored volume

[grace white]

Hi
I am about to add a new disk to a mirrored volume what I want to know is the following :

a. how do I split the volume to enable me to lvexend existing mirrored volume with new disk.
b. should I take a backup using vgcfgbackup of volume as well


The following configuration is as followed at present :

Bdf

Filesystem kbytes used avail %used Mounted on
/dev/vg01/lvol12 17776640 16272844 1410625 92% /home3
/dev/vg00/lvol6 573440 479731 87910 85% /opt


--- Logical volumes ---
LV Name /dev/vg01/lvol12
VG Name /dev/vg01
LV Permission read/write
LV Status available/syncd
Mirror copies 1
Consistency Recovery MWC
Schedule parallel
LV Size (Mbytes) 17360
Current LE 4340
Allocated PE 8680
Stripes 0
Stripe Size (Kbytes) 0
Bad block on
Allocation PVG-strict
IO Timeout (Seconds) default

--- Distribution of logical volume ---
PV Name LE on PV PE on PV
/dev/dsk/c5t9d0 4340 4340
/dev/dsk/c7t9d0 4340 4340

--- Logical extents ---
LE PV1 PE1 Status 1 PV2 PE2 Status 2
00000 /dev/dsk/c5t9d0 00000 current /dev/dsk/c7t9d0 00000 current

Thanks
Grace

[Stefan Farrelly · Accepted solution]

a. to split the volume - ie. remove the mirror so you can add in the new disk do;

lvreduce -m 0 /dev/vg01/lvol12

b. No need to to a vgcfgbackup, normal vg commands automatically do one. When you now add in the new disk using vgextend it will run vgcfgbackup.

But your problem is you have disk A (17GB) mirrored to disk B (17GB) and you want to add a third disk ? If the size of the new disk is also 17GB you wont be able to mirror it (not easily anyway). Normally to extend a mirrored lvol you add 2 new disks, one to extend the data and one to extend the mirror.

If your new disk is 36GB then youre fine, you can do it. Just lvextend vg01/lvol12 onto the old mirror disk (c7t9d0), then when you do lvextend -m 1 /dev/vg01/lvol12 it will mirror to the new disk.

If youre adding a new disk also 17GB then you should only increase vg01/lvol12 by half that amount (8.5GB) to leave enough space to mirror it all also. Even then it wont be easy to have a mirrored lvol using 3 disks (normally you use an even number of disks). It will take some precise lvextend and mirror commands to accomplish it, but it is possible.

[grace white]

Hi Stefan

Thanks for the reply there is just one thing i want to clarify with you. I have two disks both 17Gb each the new disk is 36Gb so when i come to mirror this do i just do lvextend -m 1 /dev/vg01/lvol12 not a -m2 as i thought.

Regards
Grace

[Stefan Farrelly]

Hi Grace,

yes, reduce your mirror, extend your volume to the 17Gb mirror drive which is now free, then add the 36GB drive, and when you reapply the mirror with lvextend -m 1 it will automatically use the new spare 36GB drive.

[grace white]

Great

Thanks for that.

Grace