From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: Which raid card to buy for Sarge Date: Thu, 01 Apr 2004 00:54:35 -0500 Sender: linux-raid-owner@vger.kernel.org Message-ID: <406BAE9B.6000306@pobox.com> References: <200404010529.i315TbW21661@dns1.watkins-home.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <200404010529.i315TbW21661@dns1.watkins-home.com> To: Guy Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Guy wrote: > With software RAID (md) you must invoke some commands to do the hot swap. > It's not auto-magic. Some of the hardware RAID systems I know of don't need > any user input to re-sync. Just swap the bad disk for a good one. > > It would be nice if md could detect a disk being replaced and do everything > needed without user input. Yes, agreed. This sort of communication would be the [simple] interface alluded to in other messages. > BUT!! md has a big difference on that point. > md does not mirror disks! > Read the above line again! > > md mirrors partitions. I think it is a major difference. You must No, that's not the major difference. You are very close, though: The difference is that md manipulates anonymous block devices. The block devices can be whole disks, partitioned disks, un-partition-able media (nbd or ramdisk), whatever. As long as it's a block device, md can handle it. So, functioning at the Linux block device level as it does, md is much more abstract and generic than hardware RAID, or "controller-focused software RAID" (i.e. Adaptec host raid, DDF, Promise pdcraid, hptraid, Silicon Image Medley RAID, ...) Jeff