From owner-freebsd-scsi Fri Oct 12 20:40:32 2001 Delivered-To: freebsd-scsi@freebsd.org Received: from magic.adaptec.com (magic.adaptec.com [208.236.45.80]) by hub.freebsd.org (Postfix) with ESMTP id 3B7B037B40D; Fri, 12 Oct 2001 20:40:29 -0700 (PDT) Received: from redfish.adaptec.com (redfish.adaptec.com [162.62.50.11]) by magic.adaptec.com (8.8.8+Sun/8.8.8) with ESMTP id UAA11750; Fri, 12 Oct 2001 20:40:28 -0700 (PDT) Received: from btc.btc.adaptec.com (btc.btc.adaptec.com [162.62.64.10]) by redfish.adaptec.com (8.8.8+Sun/8.8.8) with ESMTP id UAA05655; Fri, 12 Oct 2001 20:26:37 -0700 (PDT) Received: from hollin.btc.adaptec.com (hollin [162.62.149.56]) by btc.btc.adaptec.com (8.8.8+Sun/8.8.8) with ESMTP id VAA29351; Fri, 12 Oct 2001 21:40:21 -0600 (MDT) Received: (from scottl@localhost) by hollin.btc.adaptec.com (8.11.6/8.11.4) id f9D3ZgC00486; Fri, 12 Oct 2001 21:35:42 -0600 (MDT) (envelope-from scottl) Date: Fri, 12 Oct 2001 21:35:41 -0600 From: Scott Long To: Mike Smith Cc: David Greenman , Alexey Koptsevich , scsi@freebsd.org Subject: Re: Adaptec 3210S: RAID5 performance and bus throughput Message-ID: <20011012213541.B464@hollin.btc.adaptec.com> References: <20011012165318.C18001@nexus.root.com> <200110130053.f9D0rNk05668@mass.dis.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200110130053.f9D0rNk05668@mass.dis.org> User-Agent: Mutt/1.3.19i Sender: owner-freebsd-scsi@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org On Fri, Oct 12, 2001 at 05:53:23PM -0700, Mike Smith wrote: > > You only need to do two reads, one from the disk you are updating and one > > from the disk that has the parity. When you XOR the old data from the parity > > data, you've removed it and can XOR in the new data. Two reads, two writes. > > Blah. I knew my numbers looked wrong, but I was busy trying to make the > other point (you don't have to read the stripe) and instead made a fool > of myself. I wasn't very clear in my original explaination, but I meant what David and Justin said. Anyways, the point is that RADI5 writes are slow no matter how you look at it, requiring a minimum of 4 disk operations for every case that I can think of except one (write a full stripe to a 3 disk set only requires 3 operations) To get back to the original point, some cards are inherently faster than others. I don't know of any cards on the market right now that can saturate a 64/66 PCI bus, and most can't saturate a 64/33 bus. I'm not in the position to preach the pros and cons of a 3210S in public; you'll have to research that yourself. Scott To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message