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## what is the use of PE and LE?

Dear ,

What is the use of PE and LE in pv and LV?why its creating?
3 REPLIES 3
Acclaimed Contributor

## Re: what is the use of PE and LE?

This is another basic of LVM.

A disk will be divided in small "blocks" - physical extends (PE).

Logical extends will now be mapped to PEs, either 1:1 or 1:2 - in case of mirror the LE will be written to two PEs.

Hope this helps!
Regards
Torsten.

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Solution

## Re: what is the use of PE and LE?

Hi:

To add to Torsten's comments, the logical extents (LE) of a logical volume can and often do exist on different physical volumes. You have some finite number (and limit) to the number of physical extents (PE) a physical volume of a volume group has. Where you map the logical extents (LE) to the physical extents occurs during 'lvcreate' and/or 'lvextend'. Things like 'strict' and 'continguous' allocation policies govern the rules of the mapping.

A good summary of LVM can be found in the LVM(8) manpages:

http://bizsupport.austin.hp.com/bc/docs/support/SupportManual/c02261079/c02261079.pdf

http://bizsupport.austin.hp.com/bc/docs/support/SupportManual/c02023734/c02023734.pdf

Regards!

...JRF...

Esteemed Contributor

## Re: what is the use of PE and LE?

Hi,

When a logical volume is created it is divided into a number of logical extents and these extents are mapped to the actual physical disk location on the disk which are called as physical extents. This map is stored at the top of the disk called as an extent map. The default size is 4MB. At times careless use of LVM commands can lead to extreme fragmentation of the extent map which can be monitored by sar or glance.

> Torsten
I really think it's a logical "extent". Correct me if I am wrong. :)

Regards