From: Jeff Garzik <jeff@garzik.org>
To: Carlo Wood <carlo@alinoe.com>, Jeff Garzik <jeff@garzik.org>,
Tejun Heo <htejun@gmail.com>, Manoj Kasichainula <manoj@io.com>,
linux-kernel@vger.kernel.org,
IDE/ATA development list <linux-ide@vger.kernel.org>
Subject: Re: SATA RAID5 speed drop of 100 MB/s
Date: Sat, 23 Jun 2007 18:43:01 -0400 [thread overview]
Message-ID: <467DA1F5.2060306@garzik.org> (raw)
In-Reply-To: <20070623125316.GB26672@alinoe.com>
Carlo Wood wrote:
> Is it possible that the measurement with "hdparm -tT" returns a higher
> value for some setting, but that the over-all real-life performance
> drops?
IN THEORY, RAID performance should /increase/ due to additional queued
commands available to be sent to the drive. NCQ == command queueing ==
sending multiple commands to the drive, rather than one-at-a-time like
normal.
But hdparm isn't the best test for that theory, since it does not
simulate the transactions like real-world MD device usage does.
We have seen buggy NCQ firmwares where performance decreases, so it is
possible that NCQ just isn't good on your drives.
Jeff
next prev parent reply other threads:[~2007-06-23 22:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20070620224847.GA5488@alinoe.com>
[not found] ` <4679B2DE.9090903@garzik.org>
[not found] ` <20070622214859.GC6970@alinoe.com>
2007-06-23 7:03 ` SATA RAID5 speed drop of 100 MB/s Jeff Garzik
2007-06-23 7:54 ` Tejun Heo
2007-06-23 12:53 ` Carlo Wood
2007-06-23 17:30 ` Bartlomiej Zolnierkiewicz
2007-06-23 22:43 ` Jeff Garzik [this message]
2007-06-24 11:58 ` Michael Tokarev
2007-06-24 12:59 ` Dr. David Alan Gilbert
2007-06-24 14:21 ` Justin Piszcz
2007-06-24 15:52 ` Michael Tokarev
2007-06-24 16:59 ` Justin Piszcz
2007-06-24 22:07 ` Carlo Wood
2007-06-24 23:46 ` Mark Lord
2007-06-25 0:23 ` Patrick Mau
2007-06-24 15:48 ` Michael Tokarev
2007-07-05 22:12 ` Phillip Susi
2007-06-24 0:54 ` Eyal Lebedinsky
2007-06-24 9:01 Mikael Pettersson
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