Re: RAID performance

[Brad Campbell <lists2009@fnarfbargle.com>]

On 07/02/13 18:19, Adam Goryachev wrote:

> problem. Is there some way to instruct the disk (overnight) to TRIM the
> extra blank space, and do whatever it needs to tidy things up? Perhaps
> this would help, at least first thing in the morning if it isn't enough
> to get through the day. Potentially I could add a 6th SSD, reduce the
> partition size across all of them, just so there is more blank space to
> get through a full day worth of writes?

I have 6 SSD's in a RAID10, and with 3.7.x (I forget which x - 2 or 3 
from memory) md will pass the TRIM down to the underlying devices (at 
least for RAID10 and from memory 1).

I have a cronjob that runs at midnight :

#!/bin/sh
export TIME="%E real\n%U user\n%S sys\n"
for i in / /home /raid10 ; do
	/usr/bin/time /home/brad/bin/fstrim -v $i
done

Based on the run times, and the bytes trimmed count I suspect it works.
All filesystems are ext4. Two of them are passed through encryption, but 
that passes TRIM down also. I do not have the discard option on any 
mounts (that way lies severe performance issues).

Regards,
Brad