NeXTstep: cloning a drive
Billy.Pettit at wdc.com
Fri Mar 30 15:47:04 CDT 2007
Jules Richardson wrote:
Possibly there was a firmware "feature" in the "smaller" drive which meant
full drive capacity wasn't being utilised, but that seems like a pretty
flaw in the days when a few MB here and there was precious. If not then why
someone / something (the NeXTstep installer, presumably) would format the
drive below total capacity, I don't know.
Actually this was a very common thing (formatting a drive below rated
capacity). There are several reasons why you might want to do this.
1. One vendor is already qualified with a certain track count. The
next vendor has to match that track count or else a driver has to be
modified by the system provider. Easier (and cheaper) to force the disk
vendor to compensate.
2. A previous capacity point has been obsoleted, but the vendor has
committed to supply drives and spares for X many years. So a new drive is
downgraded to match the old drive, even if means wasting some disk area.
Believe it or not, this is usually cheaper too since the new drive is
further down the cost curve.
3. Performance increase. By only using the outer cylinders, you get a
drive that has more data per track so fewer seeks. And you are only using a
portion of the surface so the seeks are shorter, hence faster.
I remember a couple of times that end users discovered this and would
deliberately damage drives to get warranty replacements. The replacement
drives could give 30-50% performance improvement. (One Special case turned
a 700MB SCSI drive into a 350MB drive. It really screamed through the
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