From: Valdis.Kletnieks@vt.edu
To: Helge Hafting <helgehaf@aitel.hist.no>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Are linux-fs's drive-fault-tolerant by concept?
Date: Sun, 20 Apr 2003 15:04:18 -0400 [thread overview]
Message-ID: <200304201904.h3KJ4IZJ015475@turing-police.cc.vt.edu> (raw)
In-Reply-To: Your message of "Sun, 20 Apr 2003 12:51:54 +0200." <20030420105154.GA16451@hh.idb.hist.no>
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On Sun, 20 Apr 2003 12:51:54 +0200, Helge Hafting said:
> > These don't address the problem - if the drive won't go "ready" because
> > of a blown server platter, your data won't get overwritten but it's still
> > readable (a number of companies make good money at this).
> >
> I see. Your data is so special that you expect people to pay for
> reconstruction hoping to find something that pays for all
> that trouble and more.
No, I don't consider my data that special - I just say "screw it" and
go looking for the backups. However, my point is that it's not THAT
hard to salvage data off drives - it's easy enough that companies are
making a living doing it.
The question is regarding sites that are paranoid about shipping out
their data when such recovery is possible.
> Why would it be hard to reach the inner surfaces - the disks
> are not superconducting so the outer ones do not shield the
> inner ones from a strong magnetic field. You should be fine
> as long as the field extend far enough to get the entire
> drive. A high-frequency device might have trouble,
> but you don't need that - even a static field will do.
I didn't say it was impossible - I said you had to use a degausser that
was up to the task. A degausser that is rated to bulk-erase tape media
is probably *NOT* sufficiently strong to do a multi-platter disk. Most
tapes need 350 Oe or so to bulk, while disks are in the 1500 Oe range.
And you need a really big-ass magnet to make a 1500 Oe field big enough to
cover an entire disk (especially if it's an older disk of the 5.25 or
even larger variety - older IBM mainframe disks were up to 14" platters).
The Canadian government seems to agree - they recommend either getting the
degaussing wand between the platters (page 10) or using a cavity degausser
(page 12). Note that they do *not* certify cavity degaussers for disk drives
over 3 1/2" with a coercivity over 1100Oe.
http://collection.nlc-bnc.ca/100/200/301/ cse-cst/cse_app-ef/itspl-02.pdf
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next prev parent reply other threads:[~2003-04-20 18:52 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-04-19 16:04 Are linux-fs's drive-fault-tolerant by concept? Stephan von Krawczynski
2003-04-19 15:29 ` Alan Cox
2003-04-19 17:00 ` Stephan von Krawczynski
2003-04-19 22:04 ` Alan Cox
2003-04-20 16:24 ` Stephan von Krawczynski
2003-04-20 13:59 ` John Bradford
2003-04-20 16:55 ` Stephan von Krawczynski
2003-04-20 17:12 ` John Bradford
2003-04-20 17:21 ` Stephan von Krawczynski
2003-04-20 18:48 ` Alan Cox
2003-04-20 20:00 ` John Bradford
2003-04-21 1:51 ` jw schultz
2003-04-19 21:13 ` Jos Hulzink
2003-04-20 16:07 ` Stephan von Krawczynski
2003-04-20 16:40 ` John Bradford
2003-04-20 17:01 ` Stephan von Krawczynski
2003-04-20 17:20 ` John Bradford
2003-04-21 9:32 ` Stephan von Krawczynski
2003-04-21 9:55 ` John Bradford
2003-04-21 11:24 ` Stephan von Krawczynski
2003-04-21 11:50 ` Alan Cox
2003-04-21 12:14 ` John Bradford
2003-04-19 16:22 ` John Bradford
2003-04-19 16:36 ` Russell King
2003-04-19 16:45 ` John Bradford
2003-04-19 16:52 ` Stephan von Krawczynski
2003-04-19 20:04 ` John Bradford
2003-04-19 20:33 ` Andreas Dilger
2003-04-21 9:25 ` Denis Vlasenko
2003-04-21 9:42 ` John Bradford
2003-04-21 10:25 ` Stephan von Krawczynski
2003-04-21 10:50 ` John Bradford
2003-04-19 20:38 ` Stephan von Krawczynski
2003-04-20 14:21 ` John Bradford
2003-04-21 9:09 ` Denis Vlasenko
2003-04-21 9:35 ` John Bradford
2003-04-21 11:03 ` Stephan von Krawczynski
2003-04-21 12:04 ` John Bradford
2003-04-21 11:22 ` Denis Vlasenko
2003-04-21 11:46 ` Stephan von Krawczynski
2003-04-21 12:13 ` John Bradford
2003-04-19 20:05 ` John Bradford
2003-04-19 23:13 ` Arnaldo Carvalho de Melo
2003-04-19 17:54 ` Felipe Alfaro Solana
2003-04-25 0:07 ` Stewart Smith
2003-04-25 0:52 ` Richard B. Johnson
2003-04-25 7:13 ` John Bradford
[not found] ` <20030419161011$0136@gated-at.bofh.it>
2003-04-19 17:18 ` Florian Weimer
2003-04-19 18:07 ` Stephan von Krawczynski
2003-04-19 18:41 ` Dr. David Alan Gilbert
2003-04-19 20:56 ` Helge Hafting
2003-04-19 21:15 ` Valdis.Kletnieks
2003-04-20 10:51 ` Helge Hafting
2003-04-20 19:04 ` Valdis.Kletnieks [this message]
2003-04-19 21:57 ` Alan Cox
2003-04-20 10:09 ` Geert Uytterhoeven
2003-04-21 8:37 ` Denis Vlasenko
2003-05-05 12:38 ` Pavel Machek
2003-04-19 22:02 ` Alan Cox
2003-04-20 8:41 ` Arjan van de Ven
2003-04-25 0:11 ` Stewart Smith
2003-04-20 15:06 Chuck Ebbert
2003-04-20 15:19 ` John Bradford
2003-04-20 17:03 Chuck Ebbert
2003-04-20 17:25 ` John Bradford
2003-04-20 17:28 Chuck Ebbert
2003-04-21 9:36 ` Stephan von Krawczynski
2003-04-20 17:28 Chuck Ebbert
2003-04-20 17:44 Chuck Ebbert
2003-04-20 17:44 Chuck Ebbert
[not found] <mail.linux.kernel/20030420185512.763df745.skraw@ithnet.com>
[not found] ` <03Apr21.020150edt.41463@gpu.utcc.utoronto.ca>
2003-04-21 11:19 ` Stephan von Krawczynski
2003-04-21 11:52 ` Alan Cox
2003-04-21 14:14 ` Valdis.Kletnieks
2003-05-06 7:03 ` Mike Fedyk
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