max PV per VG

[Animesh Chakraborty]

Hi,
What is the maximum number of pv(phisical volume) per volume group ?
vgdisplay says max pv=16 but still I can have more than 16 disk per vg.
What is the correct number ?
I am using 72 GB EMC disk slice to 4 GB.

Thanks
Animesh

[Patrick Wallek]

With your EMC, you are not actually using more than 16 PVs in your VG. With the disks being divided up into slices, you are probably using more slices than 16, but not actual disks.

When I talk about slices I mean like /dev/dsk/c1t1d0, /dev/dsk/c1t1d1, /dev/dsk/c1t1d2, etc.

If you had more than 16 different scsi targets like /dev/dsk/c1t1d0, /dev/dsk/c1t2d0, /dev/dsk/c1t3d0, etc. then you would probably have a problem.

[Karthik_2]

Animesh,
Just to clarify .
You can specify the max physical volumes and max physical extents for each volume group at the time of creation.
By default max_pv is 16 and max_pe is 1016
But it can be increased to 255 and 65535 respectively.
-p max_pv
Are u seeing the number of active PV's more than the Max PV value?

Cheers
Karthik...

[Andy Monks]

As Karthik says, the limit is actually 255. However, this can only be set when you create a volume group. Once its created, it can't be changed.

[Les Schuettpelz]

Dave Fargo using Les's ITRC login...

In EMC-speak, any Symmetrix device that is seen as an individual instance in 'ioscan -funC disk' is either a hypervolume or a metavolume, and this is the PV that HP LVM counts toward the max_pv limit. OK, it could also be a gatekeeper or vcm db device, but those should never be in a volume group.

So when you say your EMC physicals are 72Gb but in 4Gb slices, this appears to mean that 4Gb is your hypervolume size. If you don't use metavolumes, you would be limited to 16 4Gb PV's in this volume group, each PV being 1 EMC hypervolume.

If you can create metavolumes, you can concatenate or EMC-stripe several 4Gb hypervolumes together, the only device being seen by HP-UX being the 'meta head' device, the others being 'hidden' as devices but their physical size is added to the 'head' device from the LVM perspective.

If you did this, each metavolume would be 1 PV in the volume group, sized at 4Gb times the number of hypers in the meta. So you could get more than 16 4Gb 'slices' into the volume group, but still be limited to 16 PV's.