Alternate disk in vgcreate

[ShivKumar_1]

Hi,
When I m try to extend a volume group, the disk which I add , goes always as a ALTERNATE link is there a way I can avoid that.
I have two LUNS of 83GB each, I want to get 166GB on my volume grp but it comes up only as 83GB. I tried difft ways but not succesful any ideas?

Thnks

[Stefan Farrelly]

The disk you add which goes as an alternate link becauase its a different path to the SAME DISK (or LUN). If you add in a second path to the same disk or lun LVM is always going to add it as an alternate link. If you want to add more disk space (not an alternate link) then you need to add in a diskl/lun which is not already in use.

If you want to avoid alternate links at all then dont add in devices which point the same disk/lun you are already using in your vg.

If you want to change the order of an alternate link then when you add it to a VG swap the order it goes in, eg;
vgexteng vgXX
Simply swap primary an alternate over.

Normally for such large volume groups >100GB you need to adjust a lot of VG parameters when you create it. You need to increase the physical extent size from 4MB up to say 16, increase the max pv from 16 up to say double, and possible max pe also if you intend to add in larger size luns to the group. It can take some trial and error until you get the settings you want/need to create a VG of 166GB.

[Tim Adamson_1]

Hi,

The 2nd disk is actually a different path to the first disk. So in actual fact you have 1 LUN with 2 paths to the same LUN. That is why when you see it as an alternate link ib vgdisplay.

If you have other LUNS available, try adding one of them to the VG.

If you aren't sure, post the ouput of ioscan -fnk so we can see what you have.


Tim

[Donny Jekels]

keep in mind everytime you use a disk in a volume group. the disk keeps a signature called the VGID.

vgexport and vgextend and some other vg commands write this info on the disk.

[Eugeny Brychkov]

If 'another' LUN is a business copy of this original LUN then it will not work until you'll change signature with vgchgid. But anyway, it's not good idea to do this way...
Make sure you created really ANOTHER LUN within disk array and none has dd'ed from original LUN. And of course, make sure that path you're adding is not alternate path to the same LUN! Attach 'ioscan -fn' and paths you're trying to arrange
Eugeny