From owner-freebsd-questions Wed Sep 15 3:40:20 1999 Delivered-To: freebsd-questions@freebsd.org Received: from freebie.lemis.com (freebie.lemis.com [192.109.197.137]) by hub.freebsd.org (Postfix) with ESMTP id 7E77A14EF4 for ; Wed, 15 Sep 1999 03:40:15 -0700 (PDT) (envelope-from grog@freebie.lemis.com) Received: (from grog@localhost) by freebie.lemis.com (8.9.3/8.9.0) id UAA40578; Wed, 15 Sep 1999 20:09:58 +0930 (CST) Date: Wed, 15 Sep 1999 20:09:58 +0930 From: Greg Lehey To: Graeme Tait Cc: Woody Carey , questions@FreeBSD.ORG, andriss@andriss.com, info@boatbooks.com Subject: Re: SCSI drive mirroring question Message-ID: <19990915200957.I30655@freebie.lemis.com> References: <37DF9B61.22D7@echidna.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.95.4i In-Reply-To: <37DF9B61.22D7@echidna.com>; from Graeme Tait on Wed, Sep 15, 1999 at 06:13:05AM -0700 WWW-Home-Page: http://www.lemis.com/~grog X-PGP-Fingerprint: 6B 7B C3 8C 61 CD 54 AF 13 24 52 F8 6D A4 95 EF Organization: LEMIS, PO Box 460, Echunga SA 5153, Australia Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-41-739-7062 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Wednesday, 15 September 1999 at 6:13:05 -0700, Graeme Tait wrote: > Woody Carey wrote: >>> What I want is a true bit by bit mirror of the entire first drive... >>> >>> Can anyone suggest something that would do it? >> >> I was under the impression that 'dd' could be used for bit-by-bit copy. >> Can anyone second this? > > I've used dd successfully to replicate a drive to an identical drive, and > it may well be much faster than file-by-file methods, depending on what > is on the drive to be copied (in particular, how full the drive is). BTW, > I believe this also copies any boot record, etc. > > But this was with the source drive mounted read-only. What would happen > if dd was used to copy a live filesystem, and when the system > wrote a given file, data was written both before and after the current > read point for dd? The data would be inconsistent. That's why we have things like Vinum. Greg -- When replying to this message, please copy the original recipients. For more information, see http://www.lemis.com/questions.html See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message