On Monday 29 December 2003 09:13 am, T. Joseph Carter wrote: : On Sun, Dec 28, 2003 at 11:47:31PM -0800, Larry Price wrote: : > This is kind of a borderline question; : > : > A disk was intentionally zero'd out using : > : > dd if=/dev/zero of=/dev/hda well... this writes 0's to every bit on the disk right? I would say that you wont be able to recover anything on the disk. The only way you could get anything is from latent image of the previous state of each bit... might want to contact the DoD, they *may* have a utility for such tasks, but i cant think of anyone that would...
: > : > however the DOS fdisk utility couldn't rebuild the partition table : > afterwards. what partition table... presumably that got zeroed too! : : Generally speaking some fdisk programs really can't cope with that. I : thought the DOS one could. I know that if the disk isn't screwy, cfdisk : will be able to fix it. not necessarily, but usually... : : A zeroing should not affect the low-level format because from the : perspective of zeroing the drive, you're operating at a logical level : rather than a physical level. well... that is a large part of what a lowlevel format does. another major part of a LLF is the interleave, set that wrong (or the geometry!), and really really nasty things happen. : : A poorly kept secret is that HDs have things like bad sectors all the time : and that the drives themselves have known for ages how to recognize : sectors that are going bad before they do. When this happens, they : silently reroute your bits to unused sectors they do not advertise as : actually being available. This screws with things like interleaving, but : nobody interleaves for a speed boost anymore. (Why? RAID finally really : does mean inexpensive disks...) Anyway, you only see bad blocks when the : drive runs out of spare sectors. True, those are called "reserve sectors, typicly drives have 1% reserve sectors to "replace" bad sectors on the fly... I dont understand how this effects interleaving... As i understand it, Interelaving is the space between the tracks (or is that cylinders). Anyway... : : In order to pull this off transparently, the PC needs a very different : picture of the drive than the drive electronics get. The PC sees a : virtualized disk, much the way Linux applications believe that they have : some 3 gigs of memory, regardless of how much RAM and swap you actually : have. Writing to the Linux memory space, or to the drive's virtual space, : has little or no real effect on the low-level representation of what's : actually stored on the platters or in the DRAM latch matrices. : : Low-level formats of drives are scary undertakings. Usually when I've : needed to do it, it was because the drive was damaged. Usually, the : reformat doesn't help matters even a little bit. Just a word of warning. Ive done this many times... its really not so scary if you use the right tools... I think Ive broken 1 out of 50 drives or so, and ive recoverd the other 49 (ok, some of those drives only worked for a day or so, but many lived happy lives for many years following...) You can use older bios low level formatting if you know all the right settings.. letting it guess can be risky though... I recommed using manufacturers LLF utility over bios LLF utilities. Jamie : : _______________________________________________ : EuG-LUG mailing list : [EMAIL PROTECTED] : http://mailman.efn.org/cgi-bin/listinfo/eug-lug -- I once witnessed a long-winded, month-long flamewar over the use of mice vs. trackballs... It was very silly. -- Matt Welsh _______________________________________________ EuG-LUG mailing list [EMAIL PROTECTED] http://mailman.efn.org/cgi-bin/listinfo/eug-lug
