From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <490EDB00.2080906@redhat.com> Date: Mon, 03 Nov 2008 11:05:36 +0000 From: "Bryn M. Reeves" MIME-Version: 1.0 Subject: Re: [linux-lvm] dmraid - where is the raid done? References: <1224269483.17821.39.camel@pc.ilinx> <49098F73.7000706@redhat.com> In-Reply-To: Content-Transfer-Encoding: 7bit Reply-To: bmr@redhat.com, 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: Drew Cc: LVM general discussion and development Drew wrote: >> Wrong list - that's for the Linux MD RAID subsystem (mdadm, /dev/md* and >> friends). You're looking for ataraid-list: >> >> http://www.redhat.com/mailman/listinfo/ataraid-list >> >> Which is the place for discussion of dmraid development. > > Evening Byrn, > > I am aware that the dm-raid list was the best one if he had a dm-raid > specific question. However from what I read it sounded like he was > interested in knowing what the differences were between ata/dm-raid > and md (software) raid. Being a lurker on both lists I felt that the > folks over at md would be a better choice. He was asking where the RAID is done in dmraid. I think the response of the MD folks to that question based on past experience, would be either very general or something like: "Huh? Go ask the device-mapper guys" ;) If you're using dmraid to activate volumes on an ata RAID / fakeraid adapter then all the RAID work is being done in the kernel by device-mapper. When dmraid activates a volume, it reads the metadata from the disk that describes the array and translates that into a device-mapper table, usually using some combination of the linear, dm-raid1, and dm-raid45 targets. These are the kernel modules that implement the RAID algorithms (dm-raid1 uses the kernel thread kcopyd to do the actual work - you'll see this process consuming some resources on a system with a busy mirror). For more information on the targets and the tables that are used to configure them see Alasdairs talks on LVM/device-mapper here: http://people.redhat.com/agk/talks/ Regards, Bryn.