Physical Extent Size 18Gb vs. 36Gb disks

[Dan Hardison]

I have two new rp2470s, one has 2-18Gb drives and the other has 2-36Gb drives. I just noticed today that the 36Gb system's PE size is 8Mb (vg00). The 18Gb system has a 4Mb PE size (vg00).

Should the PE size for the 36Gb system be set at 8Mb instead of the default 4Mb? Both systems are running 11.00.

TIA,
Dan

[Patrick Wallek · Accepted solution]

For the new large disks, I would go almost exclusively with the 8 MB PE size. The reason for doing is this is because all LVM information MUST fit within 1 PE on the disk and with the newer larger disks, that is sometimes not possible when you use the default 4 MB PE size.

Read thru this document for further explanations of PE_SIZE and how to avoid the "File too large" error when creating VGs on large disks.

TKB Document ID KBRC00009036:
http://www2.itrc.hp.com/service/cki/docDisplay.do?docLocale=en_US&docId=200000062909773

Also have a look at this document - TKB Document ID KBRC00008114:

http://www2.itrc.hp.com/service/cki/docDisplay.do?docLocale=en_US&docId=200000062908984

[A. Clay Stephenson]

In large measure, it doesn't matter. You are allowed a maximum of 64K physical extents per physical volume. As long as PE size (in MB) X PE's is less than the physical volume size, you are ok. There can be some small performance benefits to smaller PE sizes if you are doing extent based striping. Even in that case, the benefits are small because the smallest extent is still a very large IO chunk - thus it really doesn't matter.

[Dan Hardison]

Thanks for the replies gentlemen! Points are comin' your way.

Dan