[CentOS] LVM RAID0 and SSD discards/TRIM

Tue Aug 20 18:24:43 UTC 2013
Joakim Ziegler <joakim at terminalmx.com>

These are Crucial M4s.

Joakim Ziegler  -  Supervisor de postproducción  -  Terminal
joakim at terminalmx.com   -   044 55 2971 8514   -   5264 0864

On 20/08/13 5:20, Dennis Jacobfeuerborn wrote:
> 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.
> Regards,
>     Dennis
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