PE and LE

[shruti_1]

can anyone tell me what is th diff between LE and PE

[Ludovic Derlyn]

Hi,

PE physical extend
Physical volume is broken into PE
LE Logical extend
Logical extend is a pointer to a physical extend on disk

regards

L-DERLYN

[Torsten.]

LVM is using LE and PE to "hide" the hardware and provide more flexibility.

PE are the physical extends on the disks, logical extends are "virtual" extends. The system is accessing the LEs, almost no matter where the associated PEs are. So you can create LVOls spreading several disks, but the LVOL looks like a whole disk.

Not sure if this is a good explanation.

[Arunkumar.B]

Hi Shruti,

Actually PE is Physical extents of the disk.By default it will be 4 MB.

Diff PE & LE

PE --- Physical for the entire disk starts from 0000 to xxxx to the end of the disk

LE --- Logical extents for each logical volume starts from 0000 to xxxx upto the space which u allocated for eahc LV

Cheers
Arunkumar.B

[ricky2 · Accepted solution]

Hi Shruti!!

The smallest allocatable unit of space in LVM is known as an "Extent." A physical volume is
broken into "Physical Extents" (PEs), which are made available for allocation when the
physical volume is added to a volume group.
A logical volume consists of a series of sequentially numbered "Logical Extents" (LEs). Each
logical extent is nothing more than a pointer to a physical extent on disk. Larger logical
volumes have more logical extents, and smaller logical volumes have fewer logical extents. In
order to make a logical volume larger, LVM needs only allocate some additional extents.
The PE and LE sizes are consistent throughout a volume group, and may be set when the
volume group is initially created. The default extent size is 4 MB.

Hope this helps...

Regards,
Sanjeev

[Torsten.]

see also:

http://en.wikipedia.org/wiki/Logical_volume_management

[Robert-Jan Goossens_1]

example.

# vgdisplay -v vg00 | grep -i "pe size"
PE Size (Mbytes) 4

# lvdisplay -v /dev/vg00/lvol4

LV Name /dev/vg00/lvol4
VG Name /dev/vg00
LV Permission read/write
LV Status available/syncd
Mirror copies 1
Consistency Recovery MWC
Schedule parallel
LV Size (Mbytes) 1200
Current LE 300 <---
Allocated PE 600 <---
Stripes 0
Stripe Size (Kbytes) 0
Bad block on
Allocation strict
IO Timeout (Seconds) default

--- Distribution of logical volume ---
PV Name LE on PV PE on PV
/dev/dsk/c1t2d0 300 300 <-
/dev/dsk/c2t2d0 300 300 <-

LE = logical extend
PE = Physical extend

in above example current LE size is 300 * 4MB = 1200 MB, PE size is 600 * 4MB = 2400MB. 2400MB Because this logical volume is mirrored. 300 PE on disk C1t2d0 and 300 PE on disk c2t2d0.

HTH,
Robert-Jan

[Ninad_1]

Shruti,

You must be knowing that a VG consists of physical volumes (actual disks or LUNs) or PVs.
The smallest allocatable block of a disk is called an physical extent.
Now sine LVM presents to you logical volumes - meaning logically you have grouped a set of blocks and call it as a logical volume. These blocks in the logical volume need to be mapped to actual physical blocks. This exactly is the LE (Logical extents) and PE (Physical extents).
Thus the LE in a volume will map to PE on disks.
So say 100 LEs which form a volume can be mapped to say 50 PEs from disk1 , 30 PEs from disk2 and 20 PEs from disk3 - as per your configuration or available space from disks if using default configuration.

Also hope you are clear with the strict and distributed concepts by now.

Do let know if you still have doubts.

Regards,
Ninad

[shruti_1]

hi nanad,
thanks for ur gr8 ans.
Regarding strict and distributed concept I am not so much confident.

I just know with strinct allocation policy mirror copies should be n two disks..

But have no idea regarding distributed.

[Raj D.]

Shruti ,

Here is all , you are looking for :

http://www.1402.com/documents/Logical%20Volume%20Manager.pdf


Cheers,
Raj.

[Raj D.]

Shruti ,

You must assign points to all the responses, who tried to help you,


You forum profile says:

"I have assigned points to 3 of 40 responses to my questions. "

[ try to make it 40 of 40 ]



Also You can go through this link to know the details:

http://66.34.90.71/ITRCForumEtiquette/

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadID=140137



cheers,
Raj.


(* 0 point pls.)

[shruti_1]

thanks