[NTLUG:Discuss] Re: 'Real World' Hard-drive throughput - SATA vs Ultra160 SCSI

[Bryan J. Smith]

David Simmons <dsimmons at powersmiths.com> wrote:
> Not having experience with SCSI, I was wanting to know if
> that same principle held true for Ultra160...because
> (according to the marketing) the Ultra40, Ultra80 would be
> inferior...while Ultra320 would be 'twice' as fast?

Ultra320 just means that there is enough DTR that several
Ultra320 drives can burst and get probably over 150MBps "real
world performance" (after arbitration disconnects, protocol
overhead, etc...).  Real world application of SCSI typically
means that you don't put more than 3-4 fixed disks on a bus
if they are going to be used simultaneously.

But serial is taking over parallel, and SAS is going to
replace SCSI as the preferred local/closet storage solution. 
In the new age of SAS host adapters, you're basically going
to get "hardware RAID-0/1 for free."

> I find it hard to believe that it's that simple...BUT, on a
> side-by-side comparison...and just looking for a ball park
> answer, how would they compare?

Ultra320 just means that, assuming you have Ultra320 drives,
you can get twice the DTR burst on the bus than Ultra160. 
Including all the overhead, with 3-4 disks, on a RAID
controller I can get around 150MBps "real-world" per Ultra320
channel than about 100MBps per Ultra160 channel.

If I'm using an i960/IOP30x RAID controller, then it doesn't
matter, I will get _nothing_ close to that.  I have to be
running with a StrongARM or, more recently, XScale to break
100MBps.


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