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SpidersWeb
December 2nd, 2013, 11:24 AM
The first track or so on ESDI drives, was there a standard for bad sector maps or manufacturer/OEM data or both?
Are there any tools out there that let you rewrite them?

I have a booting IBM RT, but wanted to make sure I had a spare HD at the ready, and I have two, and on one I want to do an LLF and fresh install on without losing the data already on the original drive. All 3 drives are tested - reads/writes/seeks/detects - but I can't LLF either of the two spares in the RT - and I have a theory as to why.

So the problem:

- install fresh drive on RT
- run diagnostics
- drive passes tests and detects correctly
- do LLF, it tries to read something, I get the click click click click then the machine crashes

Move drive to IBM AT with SuperStor controller:

- load BIOS tool
- detects correctly
- run LLF
- tries to read something starting with P - like P-REG or P-MAP (I can't remember, but it's P, likely 'primary')
- click click click click
- tries to read something starting with S (like 'secondary')
- click click click click
- continues with LLF
- writes something starting with "S"

Subsequent LLF on the same machine, P fails but S reads perfectly now that it's been rewritten.

I'm thinking what's happening is IBM's old tool looks for that primary map, can't find it, and doesn't know what to do.
It's just a theory. Both machines (AT and RT) are back together and under desks, the RT being a 30kg tower isn't an easy move but I can easily boot it up and do 'dd' commands to read or write from the hardware etc and report back.

(I just want to get more knowledge about ESDI under my belt before I commit to moving it to another room for a drive switch)

Also let me know if you think I'm on the write track, or not. Going through newsgroups I found the exact problem - but it was a post with no replies and I suspect the owner just sent the drive back to IBM - I don't have that luxury sadly.

SpidersWeb
December 2nd, 2013, 11:28 AM
Forgot to mention, all 3 drives are the same spec.
The drive in my example above was a Miniscribe, but using another Maxtor (identical to the original drive, even has the IBM model code sticker) I had the same thing when using it in the RT - so I suspect that'll be exactly the same in the AT if I tried it.

Al Kossow
December 2nd, 2013, 01:37 PM
The first track or so on ESDI drives, was there a standard for bad sector maps or manufacturer/OEM data or both?


Flaw maps are handled as part of the ESDI spec. See Annex A: Magnetic Disk Defect List in
http://bitsavers.org/pdf/micropolis/ESDI_spec_X3.170-90.pdf

SpidersWeb
December 3rd, 2013, 10:21 AM
Thanks Al, much appreciated.

Looks like you're not supposed to rewrite the primary bad sector map, and if you can it appears a wee bit tricky to do so. I was hoping it was something simple like the first 512 bytes of track 0, rather than a potentially write protected 'special' region to cylinder 4096! Maybe I can find another way to get it running, different VRM/AIX or similar, I'll have to experiment some more.

I've found enough references to non-IBM drives in an RT to be confident there is no manufacturer/OEM data to worry about.