From mboxrd@z Thu Jan 1 00:00:00 1970 From: Iustin Pop Subject: Re: recommendations for stripe/chunk size Date: Thu, 7 Feb 2008 06:40:12 +0100 Message-ID: <20080207054012.GA17705@teal.hq.k1024.org> References: <47AA08E7.5000801@tmr.com> <20080206202536.3316124D1D@gemini.denx.de> <20080207003116.GA23341@rap.rap.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20080207003116.GA23341@rap.rap.dk> Sender: linux-raid-owner@vger.kernel.org To: Keld =?utf-8?B?SsO4cm4=?= Simonsen Cc: Wolfgang Denk , Bill Davidsen , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Thu, Feb 07, 2008 at 01:31:16AM +0100, Keld J=C3=B8rn Simonsen wrote= : > Anyway, why does a SATA-II drive not deliver something like 300 MB/s? Wait, are you talking about a *single* drive? In that case, it seems you are confusing the interface speed (300MB/s) with the mechanical read speed (80MB/s). If you are asking why is a single drive limited to 80 MB/s, I guess it's a problem of mechanics. Even with NCQ or big readahead settings, ~80-~100 MB/s is the highest I've seen on 7200 RPM drives. And yes, there is no wait until the CPU processes the current data until the drive reads the next data; drives have a builtin read-ahead mechanism. Honestly, I have 10x as many problems with the low random I/O throughpu= t rather than with the (high, IMHO) sequential I/O speed. regards, iustin - To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html