what is PVG (Physical Volume Group)

[senthil_kumar_1]

Hi All,

what is PVG (Physical Volume Group)

[Patrick Wallek]

A group of physical volumes. It is typically used for mirroring and/or distributed striping.

# man lvmpvg

for more information.

[Viktor Balogh]

Hi,

With the help of defining PVGs (Physical Volume Groups) you can group your LUNs/disks. This is used in conjunction with the "PVG-Strict" LV policy: you don't need to feed the device files to the lvextend command and the two mirror halves will be created from separate PV groups.

For more info on the format of /etc/lvmpvg:

http://docs.hp.com/en/B9106-90011/lvmpvg.4.html
(which is the "man lvmpvg")

We use this method to mirror our LVs across datacenters. This way, in the case of loss of a datacenter we have the complete mirror because the two mirror halves will be kept in a separate datacenter.

[Raj D.]

Senthil,

lvmpvg is an ASCII file that stores the volume-group information for all of the physical volume groups in the system. The information is stored in a hierarchical format.

More details from the man page:
http://docs.hp.com/en/B9106-90011/lvmpvg.4.html

I haven't seen much usage of PVG so unless you have a specific requirement you don't need PVG.



See this also:
A Physical VolumeGroup is the possibility to separate physical disk
devices [1] within a volumegroup in a way to use them easy for mirroring
and/or extent based striping.
Usually it is quite complicated to force LVM to use dedicated physical
devices for dedicated parts of a mirror if you have several physical
devices. If you use physical volume groups you can set the lvols to
pvgstrict (lvchange -s g ...).
More ( http://fixunix.com/hp-ux/143734-pvg-hp-ux-lvm.html )


Hth,
Raj.

[Rahul Rai_1]

Hi Senthil,

Its a combination of PVs where we can associate few disks with the same size and with strict policy but the physical volume group name must be unique, now instead using vgcreate and vgextend commands, the administrator can edit this file to create PVGs

ex:-

PVG PVG0
/dev/dsk/c2d0s2
/dev/dsk/c2d1s2

[SoorajCleris]

Hi,

#man lvmpvg

==> This concept is used to give one more level of redundancy to LVM failure when you have mirroring.

1. level one is disk failure ( used with the help of "strict" policy ==> #man lvchange

2. next level is , controller failure ( used with the help of "PVG-Strict" policy ==> man lvchage"

the disks belog to same controller grouped together, so that mirror can happen with a different controller. In case of a controller failure, all the disks (data copy) belong to other controller in the mirror is available.

Regards,
Sooraj

[Pete Randall]

People:

This thread is three months old!!!!

The value of repeating advice already given is questionable when done expediently and totally wasted when done after the author has already forgotten they asked the question.


Pete

[Matti_Kurkela]

Alone, the PVGs have no significance. They have meaning only when combined with PVG-strict extent allocation policy.

For example, let's assume you have a total of four disks on two controllers (two disks on each controller), and all these four disks must belong to vg00. (In other words, an old system whose disks are so small you need more than two disks for a reasonable-sized mirrored vg00).

When you use MirrorDisk to mirror your system disk, you would like to place the mirror halves on different controllers to maximize your fault tolerance (and possibly performance too).

It *is* possible to do this without using PVGs, simply by always specifying explicitly where to place the mirror copy when setting up the mirrors. But this is prone to mistakes: if you forget, the system may place the mirror copy automatically to any disk.

With PVGs and the PVG-strict extent allocation policy, you can tell the system that you want to place your mirrors so that two halves of any mirror may not be on the same controller. Once you've configured the PVGs and set the allocation policy to PVG-strict, the system simply *won't allow* such a mistake to happen.

If your system has a only single SCSI controller, or all disks are on different controllers, there is not much point to set up PVGs.

PVGs are useful if your VG spans multiple controllers and some of the controllers control multiple disks. In that case, you define one PVG for each controller and assign the disks to the respective controller's PVG.

PVGs can be set up simply by creating the /etc/lvmpvg file and writing in the appropriate configuration: see "man lvmpvg" for details.

MK

[Pete Randall]

Well, at least Matti provided additional detailed information!

;^)


Pete