Re: Readahead with softraid1

[Jens Axboe <axboe@suse.de>]

On Fri, Jul 08 2005, Erik Slagter wrote:
> Hi,
> 
> I am using softraid 1 on two sata disks and I'm trying to get the best
> possible performance. IMHO read actions (if properly addressed) should
> be split over the two drivers and performed independently. However, I
> don't notice anything to back this up. The read performance (with the
> dreaded hdparm) shows read performance on sda,sdb and md0 exactly the
> same.
> 
> I've been playing a bit with readahead and it does matter a bit in that
> if I disable readahead for sda/sdb completely, the read rate for these
> goes completely down (to be expected) whilst the read rate on md0 stays
> the same (also a bit to be expected). Other combinations do not show any
> significant impact.
> 
> I also played with the i/o scheduler and nr_requests (as from previous
> messages here).
> 
> What am I doing wrong here???

raid1 doesn't split reads, currently you need more than one process
doing io to get a performance increase.

-- 
Jens Axboe