From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladislav Bolkhovitin Subject: Re: Performance of SCST versus STGT Date: Thu, 24 Jan 2008 15:41:35 +0300 Message-ID: <4798877F.9090702@vlnb.net> References: <20080117184052F.fujita.tomonori@lab.ntt.co.jp> <478F246C.4040400@vlnb.net> <20080117190558K.fujita.tomonori@lab.ntt.co.jp> <20080117174542.GC29650@osc.edu> <4795D4A7.5000105@vlnb.net> <20080124070616.GA31633@porcupine.cita.utoronto.ca> <4798720E.4020802@vlnb.net> <20080124114027.GC26751@porcupine.cita.utoronto.ca> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080124114027.GC26751-Td5ZOp7sT3Xw02mFwxTg32+DJq1SqhBbsOSz5zK2v9k@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: stgt-devel-bounces-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org Errors-To: stgt-devel-bounces-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org To: Robin Humble Cc: FUJITA Tomonori , stgt-devel-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org, linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, James.Bottomley-JuX6DAaQMKPCXq6kfMZ53/egYHeGw8Jk@public.gmane.org, scst-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: linux-scsi@vger.kernel.org Robin Humble wrote: > On Thu, Jan 24, 2008 at 02:10:06PM +0300, Vladislav Bolkhovitin wrote: > >>>On Jan 24, 2008 8:06 AM, Robin Humble wrote: >>> >>>>how are write speeds with SCST SRP? >>>>for some kernels and tests tgt writes at >2x the read speed. >> >>There is a fundamental difference between regular dd-like reads and writes: >>reads are sync, i.e. latency sensitive, but writes are async, i.e. latency >>insensitive. You should use O_DIRECT dd writes for the fair comparison. > > I agree, although the vast majority of applications don't use O_DIRECT. Sorry, it isn't about O_DIRECT usage. It's about latency bound or not workload. > anwyay, the direct i/o results were in the email: > > direct i/o dd > write/read 800/751 MB/s > dd if=/dev/zero of=/dev/sdc bs=1M count=5000 oflag=direct > dd of=/dev/null if=/dev/sdc bs=1M count=5000 iflag=direct > > I couldn't find a direct i/o option for lmdd. > > cheers, > robin > - > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >