From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: raid1 does not seem faster Date: Thu, 05 Apr 2007 15:19:15 -0400 Message-ID: <46154BB3.3010006@tmr.com> 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=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Justin Piszcz Cc: Iustin Pop , Al Boldi , linux-raid@vger.kernel.org List-Id: linux-raid.ids Justin Piszcz wrote: > > > 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. And it would be nice not to have to jump through hoops to get better performance... You can implement raid[01] at the user level, too, why bother to have it in the kernel? ;-) -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979