Full Disclosure mailing list archives
Re: Erasing a hard disk easily
From: "Gary E. Miller" <gem () rellim com>
Date: Wed, 14 Jul 2004 23:44:13 -0700 (PDT)
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Yo Darren! On Thu, 15 Jul 2004, Darren Reed wrote:
Have you ever actually used format on Solaris to format a SCSI disk ?
Yes, many times. The first time within a year or two of when they were founded. Their HQ was less than a mile from my old offices in Mountain View. One of my best friends sold them all their DRAM for the first few years. He would personally fly to Japan, swap an envelope of cash for the DRAM and fly back with the DRAM in his briefcase. I probably formatted my first scsi disk on a UNIX system in 1982 on a Charles River Data Systems box. I have also many times had to move disks from UNIX systems to DOS systems for low level recovery. This because many companies only provide low level bad block tools as DOS .exe files. If I have been simplifying things a bit much it is because I am not sure how many other folks out there have EE degrees, have advanced disk drive electronics experience and really need to know the nitty gritty details.
I ask because your comments here make it seem like you have not...and the lack of that experience shows in the rest of your comments, too...
Hmm, so I guess when Priam, Seagate, Shugart, Maxtor, Memorex, etc. paid me to write low level hardware tests for their disk drive production lines they hired the wrong guy huh? When I consulted to Priam I worked next to the room where they kept the magneto-optical interferometer. Engineers would pull the platter out of a marginal drive and place in on a spindle. The spindle of the interferometer sat on a 6" thick granite table set on big air donuts on a solid steel frame. The steel frame sat on a special piece of solid concrete that was isolate from the building foundation and sat directly on the underlying soil. It was so sensitive that if a big truck drove by on Oakmead Parkway they could see it in their results. Sort of understandable considering the land was sorta swampy before they built the industrial park just south of Alviso. They claimed they could read the last 7 to 10 passes on the track by the residual magnetism on the disk. The trick is not so much read/write percentages, like has been discussed here, but off-center tracking and subtle timing/speed changes. If one pass is written a few % points of track width to the inside on one pass and a few % to the outside on the next. The interferometer was sensitive enough in width to profile the overlapping tracks. When you looked at the results it was if you had tried to draw a pencil line on top of another pencil line. The small differences were detectable and discernable as two separate lines. The second effect is a peak effect. Contrary to popular opinion, disk drives do NOT write ones and zeros. For one thing disks, like T1 lines, are an AC medium and not a DC medium. So encoding it used to keep the frequency spectrum to/from the heads in a narrow range to allow for effective filtering. Then, to increase density, special codings are used, like MFM, RLL, ARLL, etc. What goes on the disk is measured in terms of flux reversals and flux peaks. In RLL 1,7 as many as 7 bits may be encoded with a single flux reversal. Here is a good reference on RLL encoding as used on disks: http://duplex.hypermart.net/books/hards/002-004.html The analogy is not exact, but you can think of it like a modem. NO analog POTS modem has a BAUD (symbol) rate over 2400. But you get the BIT rate up to 56,000 by encoding more than one BIT per BAUD (symbol). If this is unclear you should spend the $$, buy the relevant ITU specs for V.32 and read them. When you re-write a disk the flux reversals and flux peaks of the new data will not line up over that of the last data. Even if you write the same data twice, there will be subtle differences in clock speed and spindle speed that means the new data will not line up exactly on the old data in the angular direction. If you have a digital o-scope hooked up to the read head ahead of the filtering then you can see the little artifacts of the last data written. It is also plainly visible on the interferometer. I am NOT saying that this is an easy thing to do. At a big disk drive company maybe only a few people are capable of this kind of analysis and their success rate will be limited. But it can be done and I have personally seen it done. To repeat what others have said here. If the NSA wants to read your "scrubbed" HDs they probably can. As for everyone else, not much to worry about. RGDS GARY - --------------------------------------------------------------------------- Gary E. Miller Rellim 20340 Empire Blvd, Suite E-3, Bend, OR 97701 gem () rellim com Tel:+1(541)382-8588 Fax: +1(541)382-8676 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (GNU/Linux) iD8DBQFA9ifA8KZibdeR3qURAgwFAKDrz2F2k3TDaSTRKdv7HX7IymE2mACgppU/ +egmh9lgD0Kb3xnTLtUkekA= =D1xE -----END PGP SIGNATURE----- _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
Current thread:
- Re: Erasing a hard disk easily, (continued)
- Re: Erasing a hard disk easily Denis McMahon (Jul 13)
- Re: Re: Erasing a hard disk easily Maarten (Jul 13)
- RE: Erasing a hard disk easily Jos Osborne (Jul 13)
- Re: Erasing a hard disk easily Aditya, ALD [ Aditya Lalit Deshmukh ] (Jul 13)
- Re: Erasing a hard disk easily Maarten (Jul 14)
- Re: Erasing a hard disk easily Darren Reed (Jul 14)
- Re: Erasing a hard disk easily James Sneeringer (Jul 14)
- Re: Erasing a hard disk easily Larry Apolonio (Jul 14)
- Re: Erasing a hard disk easily Gary E. Miller (Jul 14)
- Re: Erasing a hard disk easily Darren Reed (Jul 15)
- Re: Erasing a hard disk easily Gary E. Miller (Jul 15)
- Re: Erasing a hard disk easily Darren Reed (Jul 16)
- Re: Erasing a hard disk easily Kurt Seifried (Jul 16)
- Re: Erasing a hard disk easily Gary E. Miller (Jul 16)
- Re: Erasing a hard disk easily Aditya, ALD [ Aditya Lalit Deshmukh ] (Jul 13)
- Re: Erasing a hard disk easily Dave Horsfall (Jul 15)
- Re: Erasing a hard disk easily Vincent Archer (Jul 15)
- Re: Erasing a hard disk easily José María Mateos (Jul 15)
- Re: Erasing a hard disk easily Denis McMahon (Jul 13)
- Re: Erasing a hard disk easily wszumera (Jul 15)