What difference between small PE size and big PE size?

[nn-tel-wq]

Hi,everyone
I sam the default PE size in vg00 is 4MB,but if I modify it ,the size can extend to 8 or 16 ... . I want to know if I extend the size of the PE ,the big PE can improv the performance. in othe words, if different PE size can affect the performance .

Thanks for your help.

[Fred.Wu]

Hi:
I don't think a big PE size can provide a performance improvement.
But when you create a vg by large disks, you have to increase the PE size, that not for a good performance, but for the limitation of the PE number per disk.

[A. Clay Stephenson]

With one very doubtful exception the answer is no. The exception is with extent-based striping. In this case you would want a smaller PE size to better distribute I/O. The problem with that is that the smalled possible PE (1MB) is still much too large to be a good stripe size. Thus the real answer to your question is no. PE's essentially form a lookup table in the kernel so that logical block n is translated into physical block p on physical device d. Larger PE's would result in a smaller table but that table lookup overhead is trivial compared to that of the actual I/O. If you need better performance, look elsewhere.

[john kingsley]

Be aware that if you using the default PE size 4 MB on very large disks or LUNS (+100GB) you will run into problems with LVM PE limits when you start creating volume groups.

[Steven E. Protter]

Hello there,

Many have asked including myself.

There is no evidence that increasing PE size helps performance. It can help with PE allocation issues but there are better ways to do that with vgcreate.

Good Luck,

SEP