What is the recommended PE size for a VG?

[pap]

Just want to know what is the recommended size for PE for a particular VG? Is there any performance constraint if we keep PE size larger?

Suppose I have a disk of 17Gb and want to select PE size, I can select 64Mb as well as 8MB, which is better and why? Apart from the smallest possible allocation size for a FS, is there any other advantage of using smaller PE size?
Thanks,
-pap

[Pete Randall · Accepted solution]

Hi pap,

With a smaller PE size, you run the risk of not being able to add larger disks to the volume group at a later date. I know of no performance penalty for using a large PE size and would suggest a middle of the road approach like 64MB.


Pete

[Bill Hassell]

The size for PE's is only a bookeeping artifact and has no meaning for physical I/O, filesystem allocation or performance. If these are large (and especially: growing) disks, select a LARGE PE (4megs is way too small). The reason for a large PE is for expansion. Once you have used all 65,536 extents, it is impossible to add any more space. The volume must be backed up, destroyed and recreated with a larger extent size. If you are starting with a 17Gb disk and plan on adding 50 more disks, you had better pick a very large PE (64megs or larger) now, before you have to start over.

[A. Clay Stephenson]

There is one possible (and dubious) reason for choosing a smaller PE size. If you are using extent-based striping then you want the smallest possible PE size that will allow you to fully allocate your largest physical disk. The smaller the PE size in this case, the grater the distribution of I/O over the disks. Even in this case, the smallest PE size (1MB) is still much too large to be a good stripe size but it might beat a sharp stick in the eye.

Since I haven't used extent-based striping in years, I would suggest that you err on the side of larger PE's.

[pap]

Thanks to all who replied. I really appreciate your valued points and decided to go for 32MB or 64MB PE size for my VGs.
Thanks,
-pap