topic Re: vgcreate option in Operating System - HP-UX

vgcreate option

Sebastien Masson — Tue, 27 Nov 2001 11:58:37 GMT

I all,

Because I run easly into trouble when I use the default max_pe and pe_size, I change both to the max value each time a build a new VG.

So I can add a new disk (or lun) into my VG without the not enought PV for PE.

Someone can tell me if, by using the max value (max_pe = 65636 and pe_size=16MB), that will cause performance problem or waste resource ?!

Otherwise why this limitation exist and that maybe a very good reason to move on VxVM.

Re: vgcreate option

Duncan Edmonstone — Tue, 27 Nov 2001 12:09:02 GMT

These figures are really governing the amount of space reserved on the disk for the VGRA. A larger number of max_pe per pv means more space on the disk reserved for a lookup table which points to all those PEs.

So the VGRA of a disk with a max_pe size of the value you are suggesting is going to take up a lot more space than a VG with smaller max_pe size.

Of course, we are still talking about KBs rather than GBs, so in a world of 72GB disks, it's not really worth worring about.

HTH

Duncan

Re: vgcreate option

Carlos Fernandez Riera — Tue, 27 Nov 2001 12:34:43 GMT

Thera some threads regarding PE Size and MAX PEs.

The correct way seem to increase PE Size to 8 MB.

I noticed last day ( nigth) that default installation from HP in 36 GB disks is using this value yet.

Re: vgcreate option

Roger Baptiste — Tue, 27 Nov 2001 13:11:32 GMT

Hi,

Here is a doc which explains it in detail:

http://us-support.external.hp.com/cki/bin/doc.pl/sid=1a325ef617d6081e9f/screen=ckiDisplayDocument?docId=200000052474625

The key thing to remember is , every disk belonging to the VG, needs to have a VG header map which contains the details of addressing every Physical extent in the VG. This header will be the size of a PE extent of the VG. So, if the PE extent is large (say 16MB), it can address more VG space and the VG can have a larger disk. If you are increasing the maximum number of PE's of a VG, it would automatically increase the size of the PE extent, since the Header map needs to be larger to address that much size.

Regarding performance issues, no- there is no performance issue at play here, unless you are not using Distributed extent striping. If you are using Distributed striping, then you would prefer to have a lesser PE extent size.

HTH
raj