Date: Thu, 16 Sep 1999 10:44:39 +0930 From: Greg Lehey <grog@lemis.com> To: Andriss <andriss@andriss.com> Cc: Graeme Tait <graeme@echidna.com>, Woody Carey <carey@roguewave.com>, questions@FreeBSD.ORG, info@boatbooks.com Subject: Re: SCSI drive mirroring question Message-ID: <19990916104439.D30655@freebie.lemis.com> In-Reply-To: <Pine.BSF.4.10.9909151041170.85886-100000@netmint.com>; from Andriss on Wed, Sep 15, 1999 at 10:45:20AM -0400 References: <19990915200957.I30655@freebie.lemis.com> <Pine.BSF.4.10.9909151041170.85886-100000@netmint.com>
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On Wednesday, 15 September 1999 at 10:45:20 -0400, Andriss wrote: > -----BEGIN PGP SIGNED MESSAGE----- > >>> 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. > > Since copying a live filesystem with dd seems dangerous, I may have > to unmount the source drive. How long do you think it will take dd to > duplicate a 9.1 Gb UltraStar 18es u2w SCSI drive, chained on a 2940u2w > controller onto another identical UltraStar? dd on a raw partition with a 64 kB block size will give you approximately the disk speed. I'd guess at about 9 MB/s for this drive, so you'd be looking at about 20 minutes. I don't know what you expect to achieve with this copying, though. You still won't have mirroring, just a copy. Greg -- 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
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