Dmitri Ivanov wrote:
The limiting factor here is how fast the disk can actually write the
bits - sorry I don’t remember what that specification was called.
What are typical hd rates for Ultra 2 SCSI?
Check your favourite manufacturers web page Seagate doesn’t admit
to any Ultra 2 drives,
but the ST318418N Barracuda 36ES2 is a 50 pin 18G drive which gives
better than 25 MBytes/sec
Formatted Internal Transfer rate, only 20 MBytes/sec External because of
the narrow bus.
The Ultra 160 ST31806LW Cheetah 36ES gives 49 MBytes/sec Internal, and
160 MBytes/sec external.
A couple of years ago I managed nearly 10Mb/sec with a P2/233 and an
Adaptec 2940 Ultra card and a 10K rpm Cheetah drive that said it could
write 15Mb/sec to the disk. Mind you I had to use some undocumented
pass-thru features to bypass almost everything the AHA driver wanted to
do for/to me… And I dedicated that drive to receiving my data… no
filesystem… might have had a partition table, but it was up to me to
avoid clobbering the other partitions!
Actually, I would like to avoid any programming on my side with this task, I
just
want to open() a file and write() data periodically. Let alone any driver
overrides >
Is that possible?
I doubt it. Perhaps Bill Flowers or one of the QNX filesystem gurus
could comment. I couldn’t get over
3 or 4 MBytes/sec sustained, even using the blockwrite function.
On the other hand, one could write functions that look like open and
write and close (more or less)
that used the passthru capability. More or less, a high speed library.
But Ultra 2 should do it. How much other PCI bus activity is there?
Well, before I can write 10M/s I have to get that data from
a DSP card (based on Texas Instruments TMS320C67x).
I guess this is the major activity. So I have about (10+10)M/s,
which should be nothing compared to 132M/s troughput
that PCI bus is capable of.
Oh and don’t forget the fan for the disk drive! They do get hot at 10K
and faster.
10K ???
10,000 revolutions per minute. The faster, the hotter >
Phil Olynyk
OBT Software Corp.
Thanks a lot!