topic Re: Max PE per PV in Operating System - HP-UX

Max PE per PV

dev44 — Mon, 12 May 2008 15:54:00 GMT

I am adding a 500GB lun to an existing volume group. In the past, when I try to extend the vg with a lun that big I get the max PE per PV error that there are not enough extents and only x extents will be used. How can I tell if this existing VG will accept a 500GB lun without actually doing the vgextend and it erroring?

Thanks,

Re: Max PE per PV

Ivan Krastev — Mon, 12 May 2008 15:59:05 GMT

Check with vgdisplay vgname.
For example:
Max PE per PV 4356
PE Size (Mbytes) 32

This can cover HDD up to 4356*32=139392MB - 140G disk.

You can change it with vgmodify.

regards,
ivan

Re: Max PE per PV

dev44 — Mon, 12 May 2008 15:59:11 GMT

Forgot to add the vgdisplay:

VG Name /dev/vgXX
VG Write Access read/write
VG Status available
Max LV 255
Cur LV 30
Open LV 30
Max PV 144
Cur PV 5
Act PV 5
Max PE per PV 14076
VGDA 10
PE Size (Mbytes) 16
Total PE 50865
Alloc PE 39998
Free PE 10867
Total PVG 0
Total Spare PVs 0
Total Spare PVs in use 0

I am thinking that I would multiply the Max PE per PV (14076) by PE Size (16) which gives me 225GB being the max size that I can add?

Re: Max PE per PV

Tim Nelson — Mon, 12 May 2008 16:04:07 GMT

That is the way to do it.

As mentioned maxPE can be changed now with the latest patch to 11.23 and/or 11.31 vgmodify.

Beware that it is somewhat involved and having a good copy of the data is a must. By the time I was done jumping through the vgmodify hoops I decided that the risk was not worth the reward and that creating new VGs and then migrating the data was my safest approach.

Please post your experience if you choose the vgmodify approach. When 100s of others are successful I just might change my approach as well.

Cheers.

Re: Max PE per PV

James R. Ferguson — Mon, 12 May 2008 16:04:39 GMT

Hi:

If you do:

# vgcfgrestore -vl -n vgNN

...you will see the value of 'max_pe'. From this you can see if you have sufficient extents to map to the full 500GB (based on the 'pe_size' from a 'vgdisplay').

You can also use 'vgmodify' to see your configuration (assuming a patched 11.23 or an 11.31 release):

# vgmodify -tv vgNN

See:

http://docs.hp.com/en/vgmodify/vgmodify_wp.pdf

Regards!

...JRF...

Re: Max PE per PV

dev44 — Mon, 12 May 2008 16:07:27 GMT

I do the vgmodify alot, so was just looking to see in advance what VG's will need to be modified.

Also, when you change the max PE per PV to say 32000, does this mean that I will always be able to add a 500gb LUN until my max PV is hit, or does that number decrease each time I add a 500gb lun?

Re: Max PE per PV

Mridul Shrivastava — Tue, 13 May 2008 03:34:16 GMT

Current values will add only 225GB approx. If you increase the value max PE per PV to 32000 you could add upto 500GB LUN.

This value will not decrease by adding LUNS the only limitation would be of MAX PVs so you can add LUNS as long as you are not crossing MAX PV value.

Re: Max PE per PV

Rasheed Tamton — Tue, 13 May 2008 08:08:21 GMT

If you modify the Max PE per PV of the VG to 32000 (32000*16), you can utilize 500GB Lun FULLY.

With your current values, even if you add 500GB LUN, you cannot use it FULLY. You will be only able to use the size by the existing values [Max PE per PV * PE Size]. So the remaining size of the LUN will be useless.

Regards.

Re: Max PE per PV

Steven E. Protter — Tue, 13 May 2008 08:30:25 GMT

Shalom,

Based on what I see, you will need to modify the volume group to fully utilize the disk.

PE size is one method.

If vgmodify permits you to modify the number of physical disks in the volume group, e.g. lower it, you might find a second path to accomplishing the same goal.

If you are using HP-UX 11.11 seems you have to rebuild the volume group.

SEP