Questions about physicall volume groups

[Santos Vega]

Hello,

I have many questions about pvgs. I hope sombody help me to understand it.

- Do have the pvgs the same function as the stripping?
- Can I create pvgs by putting them in "/etc/lvmpvg" or I have to create them in the vgcreate/vgextend steps?
- In a SG enviroment, if I add one pvg to a shared VG and I do not update the file "/etc/lvmpvg" of the other node, what could be the consecuences if the pkg migrates and the VG is activated in this node?
And the last one (sorry for such an amount of questions ...)
- Lets suppose I have a LVOL created in one pvg with two disks(stricted and distributed), and then, I lvextend this LVOL but I do not specify the pvg to extend into, therefore the LVOL could get any other disk, and instead of having two or four disks (one or two pvgs) the LVOL finally has three disks. what could be the consecuence of this?

Regards,

S.V.

[Geoff Wild · Accepted solution]

- Do have the pvgs the same function as the stripping?
No

- Can I create pvgs by putting them in "/etc/lvmpvg" or I have to create them in the vgcreate/vgextend steps?

From man page:
lvmpvg is an ASCII file that stores the volume-group information for all of the physical volume groups in the system.

Instead of using the vgcreate and vgextend commands, the administrator can edit this file to create and extend physical volume groups. However, care must be taken to ensure that all physical volumes to be included in the file have already been defined in their respective volume groups by previous use of vgcreate or vgextend.

- In a SG enviroment, if I add one pvg to a shared VG and I do not update the file "/etc/lvmpvg" of the other node, what could be the consecuences if the pkg migrates and the VG is activated in this node?
Package won't start.

There's more info here:

http://docs.hp.com/en/B3936-90100/ch05s04.html

Rgds...Geoff

[Bill Costigan]

the /etc/lvmpvg is only used when allocating new extents.

You need to do the pvcreate and vgextend to actually add the PV to the VG. During this step you can have LVM update the /etc/lvmpvg file by specifying the PVG group that you wish to add the PV to.

Once the extents are allocated the entries in /etc/lvmpvg as not all that imporatant. So while it might me good practice to keep all the /etc/lvmpvg files within a cluster in-sync it is not necessary. Only the file on the node that does the lvextend or lvcreate is used.

I'm not quite sure about the answer to your last question. I assume you are talking about extent striping. My guess is that the new extents will striped across all the disks that are now listed in the PVG while the existing extents will remain where they are.