3B1 Hard Disk Woes (Plea for HELP!)

[John B. Milton]

In article <850 at flatline.UUCP> erict at flatline.UUCP (J. Eric Townsend) writes:
>In article <1989Jul26.174524.21833 at eci386.uucp> clewis at eci386.UUCP (Chris Lewis) writes:
>>Somebody else wrote:
[ error ]
>
>According to an AT&T tech who came out and replaced the HD in
>my 3b1 (while it was under warranty), this is something that could
>be fixed from floppy-unix, if AT&T had bothered to ship a program
>that could do the super-low level format needed to test the hard drive.
Hmmm. Far too general a statement to be entirely corrrect.

>This is where I start to lose understanding of the subject, so
>I only *think* I'm correct.
Well, ok

>There are two levels of formatting:  The normal level, what "we"
>use, merely erases the disk, and sets up the base for the file system.
I can tell you've been too close to DOS land.

>There is a lower level format that actually writes the 0 block (or
>wherever the "what am I" information for the drive is stored).  This
>"what am I" information is what the 3b1 uses to format the hard drive.
>Currently, there is no way to do a "you are a X" format on a drive.
>(I've done this on IBM PClones, however. :-(

Well, there are several levels to formatting the hard disk drive. What the
diag disk does is a "low level format", that is, it sends a format track
command to the WD1010 hard disk controller chip. Oh, yeah, then how does it
remeber the old bad block table when you format a drive twice. Easy, before
formatting it checks to see if the disk about to be formatted is a UNIXpc
disk with a good VHB. If so, it reads the existing BBT, formats the disk,
then re-writes the old BBT when the format is complete. The reason is obvious:
once a bad spot, always a bad spot. I, like most people would not like to give
a bad spot a second chance. If you want to dump the old BBT, you have to trash
the VHB to make the diag disk think it's a new, raw disk. The low level format
re-writes the ENTIRE track from index to index, gaps, headers, data, everything.
There is a "sort of" lower level format which involves warping the format by
changing the gap sizes. This is done to AVOID bad spots, is very time consuming,
and not very reliable. Some of the PC "low level" format programs can do this.

What the DOS format command does is something completely different. It just
fills the disk with a pattern (FD I think). This is all it can do because DOS
has no way to tell just what kind of hard disk controller (chip) is down there.

John
-- 
John Bly Milton IV, jbm at uncle.UUCP, n8emr!uncle!jbm at osu-cis.cis.ohio-state.edu
(614) h:294-4823, w:785-1110; N8KSN, AMPR: 44.70.0.52; Don't FLAME, inform!