Volume Group Creation: PE Size

[Vincent Farrugia]

Hello,

It depends on how much data at a time you want to increase a logical volume when you need to. Usually, one does not increase it by 1 Mb only, but by several Mbs. So whether it is 4Mb or 8Mb does not really make any difference.

Just my thought,
Vince

[Roger Baptiste]

<>

If you are not using Distributed striping
(i.e, lvcreate -D y ), then you are fine
to use 8MB extents. There should not be
any problems.

< I did read somewhere on the forums that LVM data structures can only reside in one physical extent but I'm not sure what impact this has.>

Yes, it has no impact on performance. But,
since the VGDA resides on each disk of the VG and this VGDA is supposed to live on ONE extent, the extent size should be large enough to fit the VGDA. For instance, if you have a smaller VG extent (say 2MB), then it means the VGDA will be smaller , which in turn means it can address only smaller disk sizes!

For a good understanding of the nitty-gritties: refer to this document:
KBRC00004285


cheers
raj

[Roger Baptiste]

Con,

Another useful document to look upto is:

KBRC00001020

HTH
raj

[Yohanes Tjie]

Hi,

i have similiar problem.

I have 5 LUNs and each lun is 360GB capacity with raid 10.

I would like to create 1 VG (example "vgbackup") with 5 Luns arround 1.5TB in one Logical Volume.

It's possible ?

how to create ? i was give up coz the vgcreate command can't do that.

thanks.

YohanesT@berca.co.id

[Bill Hassell]

vgcreate is performing the bookeeping for addressing the physical disk. As implied, actual I/O performance is unaffected by large or small extents--it is simply the size of a chunk of disk represented in the LVM tables at the front of the disk. So as Woodisch suggested, use a large extent size and now yo can expand the VG with additional disks. Once you run out of extents, the volume must be erased and recreated to accomodate more disks. The default for -e is 1,016, max is 65,535 extents. The largest VG size (total for all the disks or LUNs) is PE * MaxExtents.

As far as creating terabyte volume groups, certainly vgcreate will do this--but it wil always fail if you don't specify a LARGE PE size. 8Mb is too small. Use -s 32. You can use a smaller PE size but then you must create a larger space for the extent map (the -e option).

Now once the volume group and lvol(s) have been created, whether you can create a filesystem on that 1.5Tb logical volume depends on the version of HP-UX you have and the latest patches. If I remember right, HP-UX 11.00 is now limited to 1Tb filesystems.

[Yohanes Tjie]

Hi Conal,

thanks a lot for your info. everythings was done now. i had configure 1.7TB in one VG with max extend size 64 (optional from SAM).

and, the lvol was create 2 lvol (50%-50%).

thanks again ... and my case can be closed now.

rgds,
Yohanes.