You're still limited to onlya few controllers in a system. There's also
the issue of concurrency. IDE drives handle one, and only one request
at a time. A SCSI drive can (and usually is) be issued commands with
tags allowing more than one active/pending command at a time. Thats why
SCSI drives fair better in multi-user environments. The better drives
all have 'smart' cache controllers on them that re-order the pending
ocmmands in a way that optimizes response and throughput in an
intelligent manner (I think seagate is calling it serpentine seek, but
whatever it is called..)
SCSI allows for many many more drives in a given system. SCSI always
has lower CPU overhead for an I/O operation (It is designed as a 'fire
and forget' protocol).
SCSI is more expensive, there's no doubt, but for larger environments,
there are clear benefits. Also in a SCSI system, a failed drives
electronics will, in most cases, isolate itself. In an IDE system a
failed drive will, at the least, make the other drives on that chain
unavailable, and in many cases make any other drives on the same
controller unavailable. SCSI systems inherintly allow for 'hot swap'
whereas IDE there is no such thing (And if your vendor tells you there
is -- he's lying).
Curt Sampson wrote:
>On Mon, 22 Apr 2002, Francisco Reyes wrote:
>
>>IDE's may have good thoughput, but their seek times can't compete with top
>>of the line SCSI.
>>
>
>Dollar for dollar, IDE has far better performance. Even including the
>cost of extra controllers (because you need one controller for each
>drive), I can get four high-end IDE drives for the price of one SCSI
>drive. There's no way any SCSI drive is going to do as many I/Os per
>second as four good IDE drives.
>
>As well, seek time isn't always important. For your log disk, for
>example, you care more about high sequential write speed.
>
>>Exactly.. since it won't be easy for you to find the best distributions
>>then it may be worth getting better hardware. :-)
>>
>
>What makes you think it won't be easy, in my case?
>
>cjs
>