HardDrive Physical Geometry vs. Logical Geometry: Safer/Faster/Greater-Storage?
O. Miso Corny
the Logical geometry and the real Physical geometry differ. That's not
unusual, but that when you run the numbers, you sometimes get a different
final total of blocks/sectors. That spooked me a bit, since you'd expect
the total blocks available to be the same regardless of which geometry you
used. And I hate the idea of not getting use out of every sector.
My thinking was that by creating a mountlist or RDB that exactly
represents the physical geometry, one can get faster performance (how
much?) and use the full capacity of the drive. Does anybody have the
facts on this?
I'd guess it varies somewhat depending whether it's a SCSI, IDE, or
MFM/RLL drive in question. I know SCSI drives (all? most?) have spare
blocks just in case some sectors go bad. I suspect newer IDE drives
(ATA/EIDE/ATAPI?) do the same. Are these spare blocks hidden/transparent
to us, and thus not accounted for in the geometry we get from the HD
makers or HDtoolBox?? Are they only divulged in the physical geometry (I
doubt it)?
Since most HD's have Multiple Recording Zones, where there are more
sectors on the outer parts of the disk than towards the center, we often
end up dealing with "average" sectors-per-track. Even when HD makers give
you the Physical geometry, they never say where the zones lie and how
densely packed each zone is. It seems to me you'd need this to maximize
speed and to use the full capacity of the drive. When i try to get this
"MZR" info from tech support they have no idea what I'm talking about.
For example, the HiSoft Squirrel Zip/Jaz tools seem to really
underestimate what the Jaz's maximum storage is. But maybe they know
something we don't? Like playing it safe?
To add to the confusion, HDtoolBox queries the drive firmware and gets a
geometry that differs from both the manufacturer's Logical and Physical
geometry. And the total number of blocks also sometimes differs. Anybody
know how to safely get maximum storage and speed from a drive?
Marcel DeVoe
You know, after reading all of this speculation, I might have tried
answering them point by point, but then the question that seems to rear
it's head above everything else is;
Are you really that cheap? ;-)
The differences between HD prep programs isn't all that significantly
different from each other, and if you were to try to second guess the
developers of those Amiga softwares, you would be delving into dangerous
territory.
Media is cheap these days, your data isn't.
--
Marcel J. DeVoe - mde...@shore.net - Team *AMIGA*
A4091scsi CV64 96 megs CDRW M1764-17" Catweasel FUSION/Emplant
A4000/060 CyberStorm MKII overclocked 66mhz - see "How to Overclock!"
and "DIY A4000 Tower for $45" @ http://www.shore.net/~mdevoe
Got an overclocking story to tell of /any/ kind?
Send it to me and I will post it to my "Overclocker's Web Page".
Daxbert
When sending commands to a SCSI device the #of heads / sectors per
track, etc... don't ever come into play. You make a request based on
block number. The controller on the physical device is responsible
for figuring out where this "actual" block exists on the drive. This
is also how the "fix-up" blocks are handled automagically. If you put
in a request for a block that's on the grown or factory defect list
the device will simply read the "fix-up" block without even a hint as
to this occuring. Therefore you won't be able to access these
"hidden" blocks directly without doing some very odd vendor specific
requests.
jm...@my-deja.com
If you are really interested in understanding SCSI (and not just cheap
;)) I suggest you read the SCSI specs. It's been a couple of years since
I downloaded them from the 'net but I am sure a yahoo search would lead
you to them.
SCSI is a nice,elegant,flexible,..., design.
ttfn,
Mike
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