From owner-freebsd-scsi Wed Apr 10 16:23:13 1996 Return-Path: owner-freebsd-scsi Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id QAA18230 for freebsd-scsi-outgoing; Wed, 10 Apr 1996 16:23:13 -0700 (PDT) Received: from sunrise.cs.berkeley.edu (sunrise.CS.Berkeley.EDU [128.32.38.121]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id QAA18213 Wed, 10 Apr 1996 16:23:09 -0700 (PDT) Received: (from asami@localhost) by sunrise.cs.berkeley.edu (8.6.12/8.6.12) id QAA19403; Wed, 10 Apr 1996 16:12:36 -0700 Date: Wed, 10 Apr 1996 16:12:36 -0700 Message-Id: <199604102312.QAA19403@sunrise.cs.berkeley.edu> To: DARREND@novell.com CC: stable@freebsd.org, SCSI@freebsd.org In-reply-to: (DARREND@novell.com) Subject: Re: Disk Mirroring From: asami@cs.berkeley.edu (Satoshi Asami) Sender: owner-freebsd-scsi@freebsd.org X-Loop: FreeBSD.org Precedence: bulk * Is there a way to mirror two disks in FreeBSD? The two different * possibilities are at the driver layer or at the filesystem layer. * I imagine the driver layer would be the easiest. Just take the * block to be written and write it out to both disks. The reason I * suggest the filesystem layer is to avoid duplicating the swap space * on both disks. It would be cool if the boot code could * automatically deal with either disk failing and still having the * system boot. Naturally, the driver should be able to deal with * either disk failing. Has anyone given this some thought? With * disks getting real cheap, it is a good way to have some fault * tolerance with out the cost or performance hit of RAID. (Actually, * I think mirroring is one form of RAID.) There is a driver called "ccd" (concatenated disk) that I ported from NetBSD. It is designed primarily for striping disk arrays but it has mirror support so you can use it to mirror partitions by just making it a mirrored 2-disk array. :) Please take a look at http://stampede.cs.berkeley.edu/ccd/ for details. I'm planning to put it into -current soon but there's a 2.1R version too. Satoshi