Creating a VG with a lot of disks

[Xavier Bibian Ingles]

Hello.
We have a new superdome with 8 CPU and 12GB ram. We are planning to install 8 SAP systems within.
Is there any problem concerning performance for creating a single VG with 50 or more disks?; or will be preferable to define 8 VG, one for every SAP?
The disk will be Symmetrics; and the intention of only one VG is not to waste disk space, because the disks are 20 GB size.

[Trond Haugen]

In my view 50 disks in one vg shouldn't be a problem in general. When evaluating performance there are always manny tings to take into considderation. But if you are able to spread the disks over more than one IO chanal that's a plus.
Also considder that making only one VG is a bit like putting all the eggs in one basket. (If that VG has problems, all SAP instances will have problems.)

Trond

[Tom Geudens]

Hi,
I'm not a SAP specialist, but instead of spreading vertically you could spread horizontally. Example. The Oracle OFA structure wants 4 different mountpoints which should be on different disks (and thus in different volumegroups). Taking your case (8 databases) I would make 4 volumegroups ...
vgora01
/oradatabase1_1
/oradatabase2_1
/oradatabase3_1
/oradatabase4_1
/oradatabase5_1
/oradatabase6_1
/oradatabase7_1
/oradatabase8_1

vgora02
/oradatabase1_2
/oradatabase2_2
... and so on

vgora03
/oradatabase1_3
/oradatabase2_3
... and so on

vgora04
/oradatabase1_4
/oradatabase2_4
... and so on

You get the idea ... :-)

If SAP has a similar structure this could solve both the performance and the diskspace problem ...

Hope this helps,
Tom Geudens

[Pete Devlin]

Following on from what Tround just said, if you do create a VG & want 50 disks remember to use the -p option (max number of physical volumes) with vgcreate as the default max pv is 16. You can have up to 255 if you want. Cheers

[Tom Geudens]

Hi,
One more point :-)
If your working with these sizes, take care to look at the -e, -s and -p parameters of vgcreate before starting to make the volumegroups.
You might run into limits otherwise !

Regards,
Tom Geudens