[ILUG] Mandrake 10
rick at linuxmafia.com
Tue Apr 27 21:15:43 IST 2004
Quoting Paul Jakma (paul at clubi.ie):
> On Tue, 27 Apr 2004, Rick Moen wrote:
> > Don't forget additional ports to support up to 15 drives per host,
> Is that not possible already? Can you not put 3 8-port controllers
> into a host? (or are you referring to the port multiplier spec? To
> allow 15 SATA ports to be multiplex to one HBA port)
Hmm, I'd have to look that up. That was based on materials I have at
home, before I left for the day.
[Future doubling of theoretical SATA bus bandwidth limits]
> Yeah, only way beyond SCSI. but hey.
See, _right here_, this is the single most spectacular pons asinorum
that ATA advocates get stuck on: A theoretical bus speed limit is
significant only if there's some prospect of ever being bottlenecked by
it. Since ATA cannot support disconnected operation (only one device
per chain can carry out operations at a time), and since all ATA drives
to date remain severely bottlenecked on physical access, the fastest of
them can barely, under absolutely ideal conditions (consecutive sectors
without seeking, single process, otherwise quiescent system, 7500 RPM
spindle speed), maybe saturate ATA/100. Minor amounts of
device-connection latency aside, there is thus _zero benefit_ from
higher ATA bus-transfer speed ceilings, almost certainly for the medium
future (2-3 years).
The design aim of U320 is to ensure that _arrays_ of current and
near-future drives (arrays being a relevant consideration, given support
for disconnected operation) are not likely to be able to saturate the
bus under real-world conditions. And guess what? It works.
When U320 starts being obsolete, I'll be out there looking at what makes
sensse then for real computing. Could be FC, could be Infiniband, could
even be some outgrowth of IEEE-1394. It almost certainly won't be any
of the ATA offerings, which seem perennially hampered by low-end design
assumptions, but we'll see.
> I fail to understand why this would be so.
Fortunately, I can live with that.
And I have no more time for what is clearly a fruitless discussion.
Cheers, "I don't like country music, but I don't mean to denigrate
Rick Moen those who do. And, for the people who like country music,
rick at linuxmafia.com denigrate means 'put down'." -- Bob Newhart
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