From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (mx1.redhat.com [172.16.48.31]) by int-mx1.corp.redhat.com (8.11.6/8.11.6) with ESMTP id iAE5iLr24826 for ; Sun, 14 Nov 2004 00:44:21 -0500 Received: from rproxy.gmail.com (rproxy.gmail.com [64.233.170.202]) by mx1.redhat.com (8.12.11/8.12.11) with ESMTP id iAE5iKuP026275 for ; Sun, 14 Nov 2004 00:44:21 -0500 Received: by rproxy.gmail.com with SMTP id f1so435879rne for ; Sat, 13 Nov 2004 21:44:20 -0800 (PST) Message-ID: <89af10f904111321441f2a3a1e@mail.gmail.com> Date: Sun, 14 Nov 2004 11:14:20 +0530 From: ashwin chaugule Subject: Re: [linux-lvm] Re: raid 1 on a single disk In-Reply-To: <87f94c37041113140053f493b0@mail.gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit References: <89af10f90411130217467c439@mail.gmail.com> <89af10f90411130241e20e2c2@mail.gmail.com> <20041113211324.GA13108@dragonhold.org> <87f94c37041113140053f493b0@mail.gmail.com> Reply-To: ashwin chaugule , LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" To: Greg Freemyer , LVM general discussion and development There Greg ! , you got it right ! The media onto which the data will be stored is a small device, that functions like a hdd, this endeavour was just for a proof of concept. I've also managed to hack into the kernel IDE susbsys. (ide-disk.c) to duplicate the writes and reads for this particular disk. So now I have two options for them. RAID 1 is useful here (although its on one disk) because , data will not be written / read _very_ often to/from the device. And in the event that the media is flaky, will provide like a backup. The other benefit is, I dont have to worry about the i/o errors (or any other for that matter) while reading the contents back, the best copy *should* be picked up by the md subsys itself. However, in my driver (modified IDE) I have to take care of the writes and reads individualy. The advantage here is that, i dont need to make 4 partitions of the disk, one is good enough, and the remaining can be unallocated. I make the write at fixed offsets into the unallocated space, and when read is requested, I read em one by one, and check. So, there. On Sat, 13 Nov 2004 17:00:35 -0500, Greg Freemyer wrote: > > > > P.S. I'd be really tempted to talk to the person asking you to do this, and ask them what they hope to achieve... > > > I can almost envision times it would be useful. i.e. disk speed is > unimportand, disk data rarely changes, but when it does it is very > important, and traditional backups are not feasible for some unknown > reason? > > By having the data written to 2 different places on the disk, the > likelyhood of a failure making it truly unrecoverable is extremely > small. > > ie. If you have disk media problems, likely only one location of the > other will be affected. > > If you have a drive electronics failure, you can ship the drive off to > have recovery performed. (Over $1000 I know, but if the data is > important.) > > Greg > > _______________________________________________ > > > linux-lvm mailing list > linux-lvm@redhat.com > https://www.redhat.com/mailman/listinfo/linux-lvm > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > -- Ashwin Chaugule Embedded Systems Engineer Aftek Infosys ltd. [Embedded Division]