From mboxrd@z Thu Jan 1 00:00:00 1970 From: Justin Piszcz Subject: Re: raid1 does not seem faster Date: Thu, 5 Apr 2007 11:57:02 -0400 (EDT) Message-ID: References: <200704011558.31670.a1426z@gawab.com> <46118473.10205@tmr.com> <200704031642.27701.a1426z@gawab.com> <461430B6.9060703@tmr.com> <20070405045819.GA5525@teal.hq.k1024.org> <20070405153138.GA12661@teal.hq.k1024.org> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: <20070405153138.GA12661@teal.hq.k1024.org> Sender: linux-raid-owner@vger.kernel.org To: Iustin Pop Cc: Bill Davidsen , Al Boldi , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Thu, 5 Apr 2007, Iustin Pop wrote: > On Thu, Apr 05, 2007 at 04:11:35AM -0400, Justin Piszcz wrote: >> >> >> On Thu, 5 Apr 2007, Iustin Pop wrote: >> >>> On Wed, Apr 04, 2007 at 07:11:50PM -0400, Bill Davidsen wrote: >>>> You are correct, but I think if an optimization were to be done, some >>>> balance between the read time, seek time, and read size could be done. >>>> Using more than one drive only makes sense when the read transfer time is >>>> significantly longer than the seek time. With an aggressive readahead set >>>> for the array that would happen regularly. >>>> >>>> It's possible, it just takes the time to do it, like many other "nice" >>>> things. >>> >>> Maybe yes, but why optimise the single-reader case? raid1 already can >>> read in parallel from the drives when multiple processes read from the >>> raid1. Optimising the single reader can help in hdparm or other >>> benchmark cases, but in real life I see very often the total throughput >>> of a (two drive) raid1 being around two times the throughput of a single >>> drive. >>> >>> regards, >>> iustin >>> - >>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >> >> Really? I have copied a file from a SW RAID1 (5GB) and I only saw >> 60MB/s not the 120MB/s the (RAID1) is capable of to the >> destination (which can easily do > 160MB/s sustained read/write). > > Did you copy it multi-threaded? I said "*multiple-readers* show improved > speed" and you said "I copied *one* file". Try copying two files in > parallel. > > I'm doing in two xterms "cat file1 >/dev/null", "cat file2 >/dev/null" > and my raid1 shows ~110 MB/s, each drive doing about half. On file only > does about 60 MB/s (this is over a PCI raid controller so the max 110 > MB/s is a PCI bus limitation). > > Iustin > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Ah, nope, I only did a single copy, I did not parallelize the operations. Justin.