Messages in this thread | | | Subject | Re: Are linux-fs's drive-fault-tolerant by concept? | From | Valdis.Kletnieks@vt ... | Date | Sun, 20 Apr 2003 15:04:18 -0400 |
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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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