VG's creation

[Marco Araya C.]

That such ... regards to all.

I have a Clariion CX.
And a HPUX 11.i
I need to create a VG of 683 GB.

My question is: which is the ideal quantity of discs that I can present and shape a VG?

Atte., Marco
Santiago - Chile

[James R. Ferguson]

Hi:

"Ideal" depends upon what you have. You need to enumerate the size(s) of your physical disk(s) and their number, for a start. You need to think about future expansion of your volume group. Look at the manpages for 'vgcreate'. The parameters you choose (e.g. 'max_pv', etc.) are *fixed* at creation time and cannot be changed thereafter. The LVM header (VGRA) must fit into one physical extent. This can constrain the values you choose.

Regards!

...JRF...

[Marco Araya C.]

But which the ideal thing for the HPUX

For example.

To create 23 discs of 30G and to form a vg of 690GB and one LV of the same size.

Or
To create 8 discs of 85GB and to form a vg of 688GB and one LV of the same size

which the ideal thing?

[James R. Ferguson]

Hi (again) Marco:

Since you are going to configure one logical volume within the volume group, whether you have 23x30GB physical disks or 8x85GB matters less than how you configure the logical volume, in my opinion.

There are still no simple answers.

Are you going to stripe (or distributed-strip) the logical volume? Are the physical disks part of an intelligent SAN with caching and/or an underlying RAID?

The mount options (with OnlineJFS) can help boost performance by bypassing the Unix buffer cache. This may be your most useful performance tweak.

From a growth standpoint, I cannot stress enough, again, to make sure that the parameters you choose for the original 'vgcreate' offer reasonable flexability. For instance, if today your physical volumes are size-X by tomorrow they are size-Y will you waste your 'max_pv' limits with too small disk or will you not be able to utilize all of their capacity because you choose too small a 'max_pe"?

Regards!

...JRF...

[Steven E. Protter]

Shalom Marco,

Specific tweak of the above.

vgcreate distributes available PE's, pysical extents based on a limit of 255 pysical disks per volume group.

If you are certain of having no more than say 10 physical disks or LUNs and want to leave room for growth, use the -p 20 parameter in the vgcreate command. This will permit you to add more physical space to the vg without having to do it over again.

Thats a rule of thumb I developed after having to recreate a bunch of volume groups a few years back.

SEP