briefly:
SCSI drives tend to be "enterprise" class devices.
SATA drives tend to be "consumer" or "nearline" (i.e., enterprise-ish
quality at consumer-ish capacities).
enterprise disks tend to have:
* higher rotational velocities
* smaller platter diameters (by as much as .5" dia)
* more platters (hence more heads)
* lower seek times
* higher throughput
* error correction data written on-track
* larger motors and voice coils (for moving heads)
* more expensive control circuitry
* much higher tolerances for vibration compensation
consumer and nearline drives tend to have:
* lower rotational velocity
* larger platters (often, as large as can fit in the case)
* fewer platters
* higher seek times
* lower throughput
* no error correction data on-track
* smaller motors and voice coils (for moving heads)
* cheaper control circuitry
* much lower tolerances for vibration compensation
The reason you get so much less capacity/$ in SCSI drives is that
SCSI is nearly exclusively marketed at the Enterprise market, where
reliability and performance are paramount, especially considering
that you can have several hundred drives in the same storage array
cabinet (hence large vibrational input from all the other spinning
devices.) The control circuitry is more expensive because it needs
to more accurately deal with head shake induced by environmental
vibration, using the more powerful voice coils to control the head.
The platters are smaller to reduce air resistance (friction) while
turning at higher velocities, lowering power consuption over larger
platters, while also reducing heat load.
It's not as simple as "the same mechanicals with different logic
boards" anymore.
Yes, I'm being rather general in my descriptions, because it's been 6
months since this was all explained to me by people who actually
design this stuff.
You really do get what you pay for, in terms of storage.
Do most of us _need_ enterprise reliability and performance? No, and
a single large SATA2 drive at 10,000rpm will blow our socks off on a
workstation. I wouldn't trust a mission-critical system to SATA
devices, though, except for using "nearline" SATA2 drives in a backup
system's virtual tape library (i.e., to-disk backups that are then
queued to tape).
At home, for my own systems, I have nothing but EIDE and SATA,
because of price concerns. At work, even though we're a university,
nothing that does anything important runs anything less than 10krpm
U320 SCSI drives. Most of the "business" systems run 15krpm U320
SCSI drives or 15krpm FC drives.
Just wanted to contribute where it felt like group knowledge might
have been lacking. :)
Gregory
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Gregory K. Ruiz-Ade <[EMAIL PROTECTED]>
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