From: John P. Looney (Kate) (jplooney-ilug at domain online.ie)
Date: Mon 03 Jul 2000 - 12:34:03 IST
On Mon, Jul 03, 2000 at 11:57:54AM +0100, Emmanuel Stone mentioned:
> Or am I on the completely wrong track and is what's below with scary
> errors about partitions not ending on cylinder boundaries what is reall
Partitions are supposed to be on a "cylinder boundary". Basic disk
Disks are made of sectors, cylinders and tracks. A track is a swarth of
disk, that goes the whole way around a disk platter. There may be many
tracks, side by side, on a platter. A drive head can read one track at a
time (the head is as wide as the track). Tracks are split into sectors.
Each sector is a multiple of 512 bytes. A cylinder is the collection of
tracks on all the disk platters, that are the same vertically aligned.
From a side view:
Assume that the X marks "track 3, on platter 0", where this hard disk has
5 metal platters, each with 5 tracks, starting at track 0, which is next
to the spindle at the middle...note a track goes the whole way around the
Now, all the x's mark a "cylinder". A partition is there so that you can
confine a part of the disk to a small area - thus concentrating disk head
movement, and so you can say "This partition, to be mounted on /tmp will
be accessed a lot, so I want it in the middle of the disk".
What's happening to you is that if a track has a thousand sectors in it,
the the cylinders are 1000 sectors long. In the partition table, there is
a field saying something like "this partiton is 3050 sectors long", and
your partition software goes "Er, that's wrong. That can't happen. It's
supposed to be 3000, or 4000, or something like that".
If effectively means that it thinks the partition table lies. And you
can't get back *working* data from that.
What you in effect have to do, is work out how big each partition was,
and remake them. You can do this by scanning the disk with something like
Norton Disk Edit, and try and work out what the start of a linux/dos/nt
partition looks like (baring in mind that primary partitions and extended
partitions look different) or guessing, or both!
> Sorry to keep pestering, I'm just in a bit of a predicament. I have no
> means of backup whatsoever and this is my only drive.
I understand. Last time something like that happened to me, it took about
twelve hours of work from me, and two people that new more about partition
tables that I do...with a hex editor and norton disk doctor...
-- The words of the unwary are apt to cause needless pain and bloody violence. - Zen Master Greg
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