Re: Hard Drive Format

[David.Empson@bbs.actrix.gen.nz]

In article <9302090718.AA26421@chasm.scar.utoronto.ca> 90taobri@CHASM.SCAR.UTORONTO.CA (Brian Tao) writes:
> The following revelation escaped Dave Huang's lips:
> > 
> > Also, though I'm not positive, I don't think SCSI lets you low level
> > format a specific track, just the whole thing. 
> 
>     That might very well be true (if the low-level format consists of a
> single SCSI command).  Maybe you could simulate a low-level format by
> writing out zeroes to the track and verifying it after?

Yep, there is a SCSI 'FORMAT' command, which does a low-level format
of the entire drive, AT THE DRIVE'S DISCRETION.  Some drives may
ignore this command, and just return an 'OK' error code.

Sure, you could write zeros out to all the sectores.  That is what
Advanced Disk Utility's 'Zero' command does.  It is NOT fast.

As I pointed out earlier, there is no way to identify a 'track' on a
SCSI drive.  I have discovered that with some SCSI drives, if a block
starts returning read errors, you can still WRITE to it, which
corrects the error.  This probably means that the block had a bad data
checksum, but the address field was still OK.

It is easiest to do this sort of thing using a block editor.  My
favourite is ZAP, from Bag of Tricks 2.  You can get ZAP to scan the
disk, stopping when it gets a read error (or reaches the end of the
disk).  You can then try writing to the problem block, and read it back
to confirm that all went OK.

Note: if the block is used by a file, that file will be damaged.  If
it is part of the directory structure, or a file's index block, you
will have major problems unless you run a disk recovery program.

> > Hmm.... don't Quantum drives ignore a low level format request?
> 
>     Not the Quantum drive I had.  I did a low-level format on it three
> times when I had it.

I think this only applies to recent Quantum drives (the ones that have
a built-in track cache).
-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand