HP-UX 11.11 Volume Group extent sizing

[John Goetz]

When creating a volume group what should the physical extent size be? 4MB is the default. Should I bump this up to the max of 256MB? Are there any pro's or con's be doing this?

[Geoff Wild]

Depends on what size disks you want (or may want) to use in the VG....with 4, you use higher then 16GB (you can - but you will only see 16GB)...multiply Max PE per PV by the PE Size to get what you want.

Rgds...Geoff

[Helen French · Accepted solution]

Well, it depends on your requirement. Accepting the default value 4MB will limit the your VG expanding capabilities in future (you cannot add a higher capacity disk in future, to the same volume group), but at the same time, it would save you the disk space. Selecting 256MB will give you the maximum limit of expandability, but could waste a lot of space (1 PE will be 256MB!). File size allocation does matter in these cases. Select the one which will suit for your requirement and future expansions. I would say 8 or 16 would be good in most cases.

[Geoff Wild]

Well my last post didn't appear right - with 4 PE - max disk size is 17GB - plus, after you create the vg - you can NOT change that parameter - you have to start from scratch....8 PE gives you almost 33 GB and 16 PE = 68GB.

No points for previous reply.

Rgds...Geoff

[A. Clay Stephenson]

It really depends upon the size of the largest anticipated disk in the VG. This is really just a bookkeeping value and has no performance implications -- with one dubious exception. If you are doing extent-based striping then a smaller PE size is favored to better distribute I/O but even the smallest possible PE size (1MB) is much too large to be a good stripe size. A very large PE size can also mean that space at the end of the disk might be wasted whereas a smaller PE would allow the disk to be used completely.