Physical extent size.

[unixguy_1]

Dear Friends,

how to assign the phyical extent size.

Pls any one guide me step by step.

Regards,
Unixguy.

[john123 · Accepted solution]

PE size to be set when u create the VG and this can not be changed later without recreating VG..

use vgcreate -s PESIZE to specify PE size..

See man vgcreate for details

[saravanan08]

for setting physical extent size

vgcreate -s (pesize) -e (maximum pe per pv) vgname physical volumes

example

vgcreate -s 4 -e 65530 /dev/vgo1 /dev/dsk/c1t0d1

thank u

[unixguy_1]

ok but sometime PE sizes is ,we are giving the 8 r 16 r 32?

what's the differnece?

it means why we are giving like that,best we give to same size to all Physical extent.

Pls anyone help me.

Regards,
Unixguy.

[Ganesan R]

Hi Unixguy,

PE size is same for all the physical extends in a volume group.

PE is the smallest size of the disk size can be allotted to logical volumes.
When you add a new disk to the LVM the total space of the disk will be divided into multiple PE's. Later on these PE's will be alloted(mapped) to logical volumes.

minimum PE size is 4MB and the maximum is 256MB. PE size is multiple of 4's.
There are some application like oracle may need big PE size for fast write operations.In that case we may need to specify big PE size when create the volume group.

Hope this helps

[unixguy_1]

Hi Ganesan,Saravan,

Thanks a lot........

I closed this call.

Regards,
Unixguy.

[Matti_Kurkela]

One PE is the smallest unit of disk space you can allocate. If you set PE size to 256 MB and your client requests e.g. a LV of 1.33 GB, you cannot do it exactly:

5 x 256 MB = 1.25 GB, too small
6 x 256 MB = 1.5 GB, a bit too big... but usually that is not a problem.

Smaller PE size allows more precise disk allocation. Larger PE size allows larger PV sizes, leading to larger VG maximum size.

At the VG creation time, you define PE size, Max PE per PV and Max PV parameters for the VG. These will set a hard limit to the maximum size of your VG.

With older versions of HP-UX, the only supported way to change these parameters was to destroy and re-create the VG.

Newer HP-UX releases contain a "vgmodify" command which may allow you to modify some of these values without destroying the VG. (It has certain limitations: read the man page before using it.)

For example: if you're setting up a data VG that will be contained in an external storage box of 8 SCSI disks, find out the size of the largest-capacity disk you can use in the box.

Choose the PE size so that

(size of largest disk) / (PE size)

is less than the absolute maximum number of PE per PV = 65535 extents.

MK