On Wed, Nov 7, 2018 at 7:26 PM Greg 'groggy' Lehey <grog@lemis.com> wrote:

On Wednesday, 7 November 2018 at 10:14:20 -0500, Clem Cole wrote:
> On Wed, Nov 7, 2018 at 9:09 AM <ron@ronnatalie.com> wrote:
>
>> The DEC drivers just left off the last 72 sectors. There was no
>> provision using them for block replacement.
>
> Minor update -- *no dynamic replacement provision*. There was a
> standard alone utility called BAD144 that implemented DEC Standard
> 144 (Bad Blocks).

Yes, this was also present in early FreeBSD distributions. I have a
vague recollection that people warned against using it.

It was OK for the super-duper old IDE drives from the IBM/AT and 80386 era. It was better for the ESDI drives because those tended to ship with a list of bad blocks printed on the label (which was itself a carry over from the MFM days). The MFM drives *did* have a DEC standard to list bad blocks and reserve spare cylinders which was derived from the earlier rkXX drives. bad144 was for the rkXX drives and then adopted, badly, for the newer drives types and wasn't super-great by the time FreeBSD came along...

Warner