Creating multiple vg

[BOMBA_1]

here it is my configuration:

- Partition of a superdome with two HBA
- Clariion FC 4700 array
- 8 LUNS (differents size) created on my array for this partition (3 LUNS on one HBA and 5 on the other).
- Each LUN will be dedicated to one Filesystem.
- The LUNs are created for Oracle.

My question is: Is it necessary to create more than one vg to increase performance.
Thanks

[Stefan Farrelly · Accepted solution]

No, creating > 1 VG is no aid to performance. It is an aid to administration for all your data disks to be in a single VG (eg vg01). We run all our large Oracle servers with hundreds of GB each in a single VG without any problems.

[Michael Tully]

I agree with Stefan. One single Volume group can have up to 255 LUN's, 255 logical volumes which basically adds up to plenty of space.
We run informix databases, and as a guide we have one volume group which is over 250Gb.

The more VG's the more administrative overhead.

[George Petrides_1]

You might want to increase the maximum number of physical volumes (disks) in the group though. The default is 16 and if you want to add more than 16 after the creation, it's impossible. So, I suggest vgcreate -p 32 /dev/vg....
(32 is just a number that I use, you can go 40 or more, however there is a limit of 1TB between the number of physical volumes and the maximum physical extends of the disk - each physical extend is 4MB by default).
I definately thing it's better having only one Volume Group, in fact I see people who only put only one disk per volume group and that defeats the purpose of the LVM manager that lets filesystems span on more than one disks (I guess these guys never had to deal with file systems on partitions... God what a nightmare that was...)
Hope this helps,
George

[V. V. Ravi Kumar_1]

hi,
performance is strictly related to number of luns and lun size. u can have a single vg with out any problem. it will further enhance performance if u enable striping on lv level to stripe across all the luns.

regds

[BOMBA_1]

Thanks for your answers,
So I don't need to create more than one vg.
I don't unterstand the interest of striping in my case, perhaps I dont't told you everything about my configuration:
my 8 luns are created (in a clariion array) in a raid group 1/0 of 4 physical disks. So my luns are already striped.
In that case, i'm not sure that striping lv will increase the performance.
Is it right or not?
Thanks

[Thomas J. Harrold]

Odds are that you will *not* improve performance by further striping. Depending on your I/O patterns, you could even hurt performance. It all depends on the type of I/O that you are doing, and the size of the I/O requests.

Oracle does recommend that you use as many physical disks as possible, so you might want to consider re-configuring your clariion array to spread your LUNs across more disks on the back end.


-tjh

[Nick Wickens]

I would like to add that there may be a case for multiple volume groups as regards performance if you want to guarantee that different applications are not accessing the same disks.

For example we run several Informix "instances" on the same machine and each instance has its own volume group(s).

In this way I can be sure that abnormal disk activity on one database can have no impact (particularly if on seperate I/O channel) on the other - usefull if you run live and development work on the same machine.

You could of course do this within one volume group if you were carefull with your disk allocation to each lvol but this would require closer administration.

If you are running a RAID 5/SAN sort of setup you would also need to ensure that the LUNS do not share the same disks as well.