🚀 go-pugleaf

In article <40043@ames.arc.nasa.gov> lamaster@ames.arc.nasa.gov (Xugh
LaMaster) writes:
+---------------
| 4)  Don't hold your breath on real I/O bandwidth.  The challenge will be to
| put enough in there to get something reasonable out of the CPU.  I think
| 10-40 MBytes/sec is probably doable for KMs.  Cray can get over 10MB/sec
| through the filesystem on *one* 12MB/sec disk; so could a KM...
+---------------

FDDI is 12.5 MB/s peak. Most KMs have some sort of FDDI board available
at this point, though the throughputs are somehwat disappointing at present.
However, we will see some KMs handling a full FDDI's worth of data by the
end of this year, even over VME busses. But many pundits already see FDDI
as "too slow" for a back-end I/O channel...

The ANSI X3T9.3 HPPI-PH interface (formerly Cray "HSC") is either 125 MB/s
or 250MB/s (that's "bytes", boys 'n' girls, not "bits"), depending on whether
you choose the 32- or 64-bit data path. Some KMs already have HPPI interfaces
which, as you might imagine, can't suck the pipe at full steam yet. By 18
months from now, that will have changed, as network and channel interfaces
start speaking directly to system memory busses, bypassing traditional
"I/O busses" such as VME.

X3T9.3 is also looking at a Fiber Channel (FC) version of HPPI. At least two
companies offer single chips *today* which take HPPI-speed 32-bit-word streams
and serialize them into gigabit/sec bit-serial streams, and vice-versa. The
holdup right now is affordable fiber-optoelectronics at gigabit speeds, but
that will change. And in the mean time, people are considering going back
to *copper* (but still bit-serial to keep the cables small) for "I/O bus"
distances, since wire is still cheap. [Yes, you can run at 1 Gb/s over cheap
coax, for some 10's of meters. That's about the same distance as HPPI-PH.]

The X3T9.3 meeting this week is considering possible ways to glue HPPI and
IPI-3 together. Fast future disks may (or may not) use IPI-3. Myself, I'd
like the disks to speak HPPI-FC directly, or something equivalent.

All in all, I think the KMs will have the I/O capability. It will just
be a little slower in coming than we'd like, and that due more to delays
in getting fast I/O devices at "KM prices" than in getting fast paths
into the KMs themselves.

And given HPPI (especially HPPI-FC), the idea of SC's as file servers
for KMs isn't totally ridiculous...

-Rob


-----
Rob Warnock, MS-9U/510		rpw3@sgi.com		rpw3@pei.com
Silicon Graphics, Inc.		(415)335-1673		Protocol Engines, Inc.
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