PVG Strict-mirroring

[Woo Kim Chye]

Hi,
I am quite new the system administration. Can someone explain to me what is PVG strict-mirroring? What is the different between it and the normal normal mirroring?
Thanks.

[Robin Wakefield · Accepted solution]

Hi,

If you man lvmpvg, you'll see you can define physical volume groups associated with a particular vg. In this way, you can, say, separate out groups of disks that are on the same controllers, for instance.

When you define you LV to be PVG-strict, you're asking the system to obey the lvmpvg "rules", so that disks within one PVG are only mirrored with disks in a separate PVG, i.e. on different controllers.

Normal mirroring just ensures that the *different* disks must be used, but they may be on the same controller - if you lose the controller, you lose both halves of the mirror.

Rgds, Robin.

[Vincent Farrugia]

Hello,

Quoting from man lvchange:

"Mirror copies of a logical extent can be allocated to share or not share the same physical volume group.

PVG Strict-mirroring is when the mirror copies share the same volume group. Using:

lvchange -s y

enables strict allocation policy, but the mirrors of a logical extent cannot share the same physical volume.

lvchange -s g

sets a PVG-strict allocation policy. Mirrors of a logical extent cannot share the same physical volume group. A PVG-strict allocation policy cannot be set on a logical volume in a volume group that does not have a physical volume group defined."

HTH,
Vince

[James R. Ferguson]

Hi:

"PVG" stands for Physical Volume Group. PVG-mirroring allows you to gain the benefit of both striping *and* mirroring. With standard LVM stripes, mirroring is not (directly) allowed.

To insure that the mirrored extents of a logical volume can be placed on disks that are not connected to the same channel, you can create physical volume groups.

This makes it much easier to create mirrors yet maintain strict allocation policy where mirror extents do not share a common disk or physical volume group.

Have a look at the man pages (1M) for 'lvcreate' and 'vgcreate' for more information.

Regards!

...JRF...

[Vincent Farrugia]

In the above thread:

PVG Strict-mirroring is when the mirror copies share the same volume group.

should read

PVG Strict-mirroring is when the mirror copies cannot share the same volume group.

Apologies,
Vince

[Sanjay_6]

Hi Woo,

Try this link,

http://docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/B3936-90053/B3936-90053_top.html&con=/hpux/onlinedocs/B3936-90053/00/00/34-con.html&toc=/hpux/onlinedocs/B3936-90053/00/00/34-toc.html&searchterms=pvg%7cstrict%7cmirroring&queryid=20011210-102657

Hope this helps.

Regds