[conspire] Advice on Building a Computer

[Rick Moen]

Quoting Adrien Lamothe (a_lamothe at yahoo.com):
(I guess, quoting Mark Weisler?):

>> Well, I found a source for some new 68pin LVD SCSI drives, new...
>> 73GB SCSI Seagate LVD 10KRPM U320 4MB 68pin ST373307LW
>> for $123 each. Also some Cheetah's for $200 each. So, I'll proceed
>> with the SCSI plan.
 
> You may want to check those drives, to insure they will configure
> properly. Rick told me an interesting story about some aftermarket
> SCSI drives, new ones, that were intentionally crippled by the
> original system manufacturer so as to be not as configurable. They
> were perfectly good drives, but only if you used one of them per
> computer (I think that was the limitation, may not remember it
> correctly. Rick can correct me).

Long ago, there was a cheap-computer-parts firm called NCA Computer
Products, which had several stores in the Bay Area, including a smaller
one on El Camino Real in Palo Alto and the main store on Lawrence
Expressway, Sunnyvale, right near Central Expressway.  The latter did
huge volumes of business, including on cheap hard drives.  They also had
a returns line that snaked out into the parking lot.

I bought an inexpensive IBM SCSI drive there, and found after some
experimentation that it refused to function on any SCSI chain that
attempted to operate in disconnect mode.  Disconnect mode is one of the
prime advantages of SCSI:  The HBA issues instructions to the device
electronics to carry out some operation, and then disconnects from it --
allows it to carry out that instruction independently without
babysitting through the end of the operation, so that the HBA can at the
same time be issuing instructions to other devices.  The net result is
that, in sharp contrast to a PATA (parallel IDE) chain, a SCSI chain's
devices can all be reading/writing simultaneously (which is why a SCSI
chain's theoretical bus throughput limit in some cases actually matters,
while PATA's was always pretty much a joke, since individual devices
were slow, and bandwidth draw was never additive under any
circumstances).

Anyhow, this particular SCSI drive didn't work with disconnected mode
enabled, at all.  

I called IBM to open an RMA case, and was referred to Tandem Computer,
since my drive turned out to have a Tandem-OEM serial number, and not a
regular IBM one.  Essentially, Tandem had made a bulk deal for cheap
drives from IBM for a model that had only that one hard drive on a SCSI
channel, in which scenario disconnected operation wouldn't have mattered
or been useful, so that support was omitted from the electronics.
Tandem probably had overstock, sold it off cheaply, and that overage
ended up resold even more cheaply to NCA Computer Products.

I drove back down from S.F. to Sunnyvale, stood in the huge long line,
and swapped the IBM under "store warranty" terms for some other HD.

Anyhow, Mark, you could verify with the "source" what S/Ns the units
have (to determine whether they're OEM models), or you can ask the
vendor whether they're OEMed.  Or you can just take a tiny chance, since
these are discontinued drives anyway and probably out of warranty -- and 
rely on "store warranty" remedies and such.