PVG mirrors?

[thinphony]

Hi!
Should anyone kindly give me some clear idea about the difference about PVG mirror and mirror & in which case they are used?


Thanks in advance.
thinphonny

[Tom Danzig]

Physical Volume Groups allow you to group disks together so that when you create mirrors, they are spread accross the disks you intended.

[Denver Osborn]

be sure to refer to the man page for lvmpvg, it gives an example for setting up the /etc/lvmpvg file.

Let's say you have vg03 and it contains 6 physical volumes. You could create an /etc/lvmpvg file with the following.

VG /dev/vg03
PVG pvg0
/dev/dsk/c0t2d0
/dev/dsk/c0t3d0
/dev/dsk/c0t4d0
PVG pvg1
/dev/dsk/c1t2d0
/dev/dsk/c1t3d0
/dev/dsk/c1t4d0

Now if you have an lvol1 in vg03 that is contained on c0t2d0 and c0t3d0 you can extend it to mirrored copies of 1 by specifing the PVG that contains pv c1t*d0

# lvextend -m 1 /dev/vg03/lvol1 pvg1
It'd be the same as
# lvextend -m 1 /dev/vg03/lvol1 /dev/dsk/c1t2d1 /dev/dsk/c1t2d2

You could see that if you are working with several disks it may help with keeping track of how things are layed out on the system.

[Dan Hetzel]

Hi Denver,

Good explanation, but I guess that last lines should read:
---------------
It'd be the same as
# lvextend -m 1 /dev/vg03/lvol1 /dev/dsk/c1t2d0 /dev/dsk/c1t3d0
---------------

Shouldn't they ?

Dan

[Denver Osborn]

yup, it should've read that way. once again I was thinking one thing and typing another. oops.

[Dan Hetzel]

Hi,

One more point, you do NOT need the PVG to mirror your LVOLs, it's just a bit more convenient because it saves typing (see Denver's answer above)

Dan

[thinphony]

Thank you all for quick reply.
But can I make two PVs as a mirror without PVG?
then why I use PVG?
What's the differences?


Thanks!
thinphony.

[Darrel Louis]

Don't know if you're using hpux 10.20 or hpux 11.X
Check the man page for lvsplit and lvmerge aswell.

Within hpux 11.X you can specify which PVG you want to split.
e.g.
# lvsplit -g PVG1 /dev/vg04/lvol1
This functionallity wasn't in the previous version of hpux. This can be handy for instance when you have a three way mirror.

Good luck

[Rob Mallard · Accepted solution]

PVGs are usually used to group PV by controller to increase performance. LV can be mirrored on the same disk, on two different disks (default), or on two different PVGs. This is controlled by the -s option (strictness) of lvextend -m

lvextend -m 1 -s n ... (allow mirroring on same disk)

lvextend -m 1 -s y ... (mirrors can not be on the same disk - DEFAULT)

lvextend -m 1 -s g ... (mirrors must be on different PVG)

Setting up PVGs in the /etc/lvmpvg file allows PV location to be defined once. You can build your own /etc/lvmpvg by hand or use the -g option of vgcreate when creating the volume groups.