[CentOS] LVM RAID0 and SSD discards/TRIM

Tue Aug 20 10:20:01 UTC 2013
Dennis Jacobfeuerborn <dennisml at conversis.de>

On 19.08.2013 20:28, Joakim Ziegler wrote:
> I'm trying to work out the kinks of a proprietary, old, and clunky
> application that runs on CentOS. One of its main problems is that it
> writes image sequences extremely non-linearly and in several passes,
> using many CPUs, so the sequences get very fragmented.
> The obvious solution to this seems to be to use SSDs for its output, and
> some scripts that will pick up and copy our the sequences in proper
> order once it's done. I have two 512GB SSDs, and I've used LVM to set up
> a RAID0 between them.
> I've got that part running, but since I'm on CentOS 5.8 (which is what
> this application officially supports), I don't have a kernel with SSD
> discard support, and after a few days (I told you, this application is
> write intensive), things get very slow.
> Using hdparm to secure erase the drives and recreating the LVM RAID0
> gets things back to speed again, but that's obviously not ideal.
> So, from what I understand, if I can get this thing running on CentOS
> 6.4, I'll get kernel discard support, and discard support in LVM when
> running a RAID0. I'm using ext4.
> Is that correct? Will this solve my problem? I want to confirm that
> discard support works on a RAID0 of SSDs using LVM and ext4 before I
> start working on getting this legacy application to run on a newer CentOS.

What kind of SSD are you using? We use Intel 520's here and don't really 
see these kind of slowdowns.