Date: Wed, 26 Aug 2009 18:10:38 +0200 From: cpghost <cpghost@cordula.ws> To: Tim Judd <tajudd@gmail.com> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: hard disk failure - now what? Message-ID: <20090826161038.GE11739@phenom.cordula.ws> In-Reply-To: <ade45ae90908241351o56e6649cv4dfc50a8fee5aeff@mail.gmail.com> References: <1338880b0908241129p75b6845cg26d21804e118364@mail.gmail.com> <ade45ae90908241313y495832edkd87004485602a42e@mail.gmail.com> <20090824224003.0b5ac2df.freebsd@edvax.de> <ade45ae90908241351o56e6649cv4dfc50a8fee5aeff@mail.gmail.com>
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On Mon, Aug 24, 2009 at 02:51:41PM -0600, Tim Judd wrote: > >> Buy spinrite, no matter what. > > It's OS/FS independent. it works on the bits stored on the magnetic > platters, NOT on a filesystem. TiVo, Linux, BSD and Mac OSX drives > are treated the same. Bits on a magnetic platter. It's recovery > stems from the randomization and movement of the head to the sector in > question that allows it to salvage any bits it can (for example, other > recovery will abandon 512bytes if 1 bit cannot be read. spinrite will > recover 512bytes-1bit to a hard drive's spare sector once spinrite > says "i'm done working with this sector".) It leads to a very > successful rate. (Disclaimer: I'm not familiar with spinrite.) 512bytes-1bit may be read back, but you can't be sure that those are the correct bytes! IIRC, sectors are usually protected by some kind of ECC. Simply ignoring the ECC and reading raw magnetic data will all too often result in corrupt sectors. Of course, if you have out-of-band error correction or at least error detection mechanisms (like .PAR or md5/sha1 checksums), raw magnetic recovery is better than nothing, if you're desperate. -cpghost. -- Cordula's Web. http://www.cordula.ws/
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