Linux – Choice of extent size

linuxlvm

Storage system: HP Smart Array P410i. Operating system: RHEL 5.5 x86_64.

I have created a RAID 1+0 logical drive consisting of 12 disks, stripe size 128KB. With this logical drive, I'm about to create a new LVM volume group. Now, what physicalextentsize should I choose?

Best Answer

Performance-wise that should not matter very much. Back in the LVM1 days a small PE size severely limited the maximum volume size, with LVM2 those restrictions do not apply.

Physical extents mostly matters if you choose to create lots and lots of small logical volumes. In that case you might waste some disk space, if a physical extent is larger than your typical logical volume. On the other hand, choosing a very small PE size can slow down LVM tools during LVM operations (such as resizing a VG) quite a bit.

Nowadays I usually don't spend too much time on thinking about the PE size, I let my distro to choose it. If you have time and willingness, you can of course try different PE sizes and benchmark them to find out if PE size matters in your case.

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Linux Bash – How to Sort du -h Output by Size

As of GNU coreutils 7.5 released in August 2009, sort allows a -h parameter, which allows numeric suffixes of the kind produced by du -h:

du -hs * | sort -h

If you are using a sort that does not support -h, you can install GNU Coreutils. E.g. on an older Mac OS X:

brew install coreutils
du -hs * | gsort -h

From sort manual:

-h, --human-numeric-sort compare human readable numbers (e.g., 2K 1G)

Linux – Easy to expand Linux software RAID 5 with XFS. Best practices

I think you've got it right. Make sure you understand and heed the warnings regarding growing RAID 5 in man 8 mdadm.

Personally if I were growing an LVM volume, I would not be growing an existing RAID array to do it. I'd create another RAID array, create a new physvol from it, and add it to the same volume group. This is a much safer operation (doesn't involve rewriting the whole RAID5 array across the new set of disks) and keeps the size of your arrays down.

Best Answer

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