On Fri, Nov 17, 2000 at 09:10:39AM +1000, Marshall, Joshua wrote:
> I hope I'm not opening a can of worms here, but what are the real
> differences these days between IDE and SCSI performance-wise?
>
> I've been told that SCSI can handle multi-user better, but I'm just
> wondering if it's just a myth now with the performance gains that IDE
> has had of late.
The major difference between IDE & SCSI is that the SCSI system is
client-server.
The CPU asks the SCSI host "get me X", then goes on with other stuff.
The SCSI host sends a request to the drives controller. When the
drive has the data, it signals the host. When the host has the data
it interrupts the CPU and passes it across.
(There are other things like tag-queueing and request ordering that
I'll leave as an exercise to the reader.)
All this means that, unlike with IDE, the CPU doesn't have to wait
around for the drive, which is very useful in multi-user or
multi-tasking situations.
The raw speed of late model IDE drives has shot up, and with single
user machines equals or beats SCSI speed. On heavily utilised server
systems SCSI wins hands-down.
OTOH, there are cards such as the 3ware Escalade series that bring
SCSI benefits to IDE drives. They have independant channels to each
of 2, 4 or 8 drives, and appear to the PC as a SCSI host. As a benefit
you can either span the drives or make them a RAID.
It all comes down to usage patterns and cost.
As to cost, an example:
SCSI: BARRACUDA 18.4GB 7200RPM 5.9MS $826.80 ex tax rrp
ADAPTEC PCI TO ULTRA SCSI HOST ADAP FOR PC $235.30 ex tax rrp
$1062.10 total
IDE: BARRACUDA II 15.3GB ULTRA ATA/66 7200RPM 8.2MS $252.20 ex tax rrp
Which means a $809.90 ex tax price difference.
So:
Single user and/or cheapskate = IDE.
Multi-user/tasking and deep pockets = SCSI
Cheers
Paul Haddon
Technical Services Manager
Hartingdale Internet
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