linux-kernel - Re: raid io requests not parallel?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20060717002007.GA5032@suse.de>
Date:	Mon, 17 Jul 2006 02:20:07 +0200
From:	Jens Axboe <axboe@...e.de>
To:	Neil Brown <neilb@...e.de>
Cc:	Jonathan Baccash <jbaccash@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: raid io requests not parallel?

On Mon, Jul 17 2006, Neil Brown wrote:
> On Saturday July 15, jbaccash@...il.com wrote:
> > I'm using kernel linux-2.6.15-gentoo-r1, and I noticed performance of
> > the software RAID-1 is not as good as I would have expected on my two
> > SATA drives, and I was wondering if anyone has an idea what may be
> > happening. The test I run is 1024 16k direct-IO reads/writes from
> > random locations within a 1GB file (on a RAID-1 partition), with my
> > disk caches set to
> > write-through mode. In the MT (multi-threaded) case, I issue them from
> > 8 threads (so it's 128 requests per thread):
> > 
> > Random read: 10.295 sec
> > Random write: 19.142 sec
> 
> Odd.  I would expect these two numbers to be a lot closer together.
> 
> Try changing the IO scheduler on the drives and see if it makes a
> difference.
> e.g.
>   cat /sys/block/XXX/queue/scheduler
>   echo cfq > /sys/block/XXX/queue/scheduler
>   echo deadline > /sys/block/XXX/queue/scheduler
> 
> See what works best.

His cache is set to write through, 16kb direct writes in that case will
be a lot slower than the equivalent reads. 10 vs 20 seconds does not
sounds out of the question.

-- 
Jens Axboe

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/