VG best practice question

[Andreas Mueller_1]

Hello all,
I've been tasked to conduct data migration from an XP-256 array to an XP-1024 array. The data to be migrated currently resides on 5 VG's, each with one LV (about 115GB each) and it's own mount point. I'd like to change this architecture a bit, and create one larger VG with 5 lvols, and retain the same 5 mount points as before. Each lvol will be using 9 disks on one Port, and 9 more disks (LDEV) with as an alternate link on a second Port on the XP-1024. Striping is done internally within the array. What are the advantages / disadvantages to having 5 smaller VG's with one LV, versus one larger VG one with 5 lvols? System is an rp5430 (L2000-44), disks to be used are 14GB.
Thanks in advance, Andy

[Mark Grant]

The more volume groups you have, the fewer logical volumes you'll break if you accidently hose a volume group. However, the more logical volumes you have in one volume group, the more flexible you can be with reducing/increasing the size of them as time goes on. Because a disk can only be in one volume group, adding a disk to a big volume group will allow you to allocate that new space to all the logical volumes in it if you want. If you only have one logical volume in your volume group and you want to increase it by 1GB, you'll have to allocate an entire LUN to it that can't be used for anything else.

Another consideration though is that you would need to be more careful of the maximum number of physical volumes allowed in a volume group. The default is 255.

[Elmar P. Kolkman]

There is more to it than that. Especially if you're going to use cluster software. You can move disks (and thus volumegroups) from one server to another, but you can not move seperate lvols around... So if you want to be able to failover on part of your system, using a single lvol, to another system on the XP1024, you need to have it in a seperate volume group.

[Andreas Mueller_1]

To clarify, this system is using MCSG for failover, however, in the event of failover, the entire application (i.e all 5 VG's with one lvol, or one VG with 5 lvols) will need to failover.

[Trond Haugen · Accepted solution]

From a SG point of view I would have prefered one VG as it would be easier to handle in the package script. Also as all 5 lvols is needed to run the application, they might as well be in the same VG.
If you need to grow the lvols it could be easier to add "some2 disk to the one VG. As aooposed to adding "some" disk to each of the 5.

Regards,
Trond

[Elmar P. Kolkman]

If all lvols belong to the same MCSG package, it's better to use one vg, I would say...