Re: SCSI or IDE
On Sun, 24 Nov 2002 20:45, Emilio Brambilla wrote:
> > IDE and SCSI give very similar performance. Performance is determined by
> > hardware issues such as rotational speed rather than the type of
> > interface.
> I agree if you think at a single drive workstation, not if you think at a
> server with many disks making heavy i/o on the disks.
Organizations such as CERN are using IDE disks for multi-terabyte arrays.
> ATA/IDE drives/controllers lack the ability to perform "command queuing",
> so they are not much fast on many concurrent i/o requests (this feature
> will be introduced in serial-ATA II devices, I think)
Get 10 disks in a RAID array and the ability of a single disk to queue
commands becomes less important, the RAID hardware can do that.
> SCSI can queue up to 256 commands and reorder them for maximum
> performance, furthermore SCSI has been developed to be used in the server
> market, so they are optimized for servers (rescheduling commands and seek
> patterns of SCSI has been written for this kind of use!)
However benchmarks tend not to show any great advantage for SCSI. If you get
an affordable SCSI RAID solution then the performance will suck. Seeing an
array of 10,000 RPM Ultra2 SCSI disks delivering the same performance as a
single IDE disk is not uncommon when you have a cheap RAID setup.
Even when your RAID array costs more than your house you may find the
3ware RAID arrays are affordable and deliver quite satisfactory performance.
Usually they are limited by PCI speeds (last time I checked they didn't
support 66MHz 64bit PCI).
> It's true that on many entry-level severs IDE is enough for the job (and
> a lot cheeper than SCSI), but on hi-end servers scsi is still a MUST!
SCSI is more expensive, it's not faster, it's not as well supported, and it
has termination issues. SCSI is not "a must" unless you buy from Sun or one
of the other vendors that gives you what costs the most rather than what you
> btw, rotational speed speeking, how many 15.000 rpm IDE disks are
> there? :-)
None, not that I care. As long as fiber channel speeds, RAID array speeds,
etc slow the arrays of SCSI drives I use so much that they deliver the same
performance as a single IDE disk that's all irrelevant.
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