Exabyte question
Chris Kranz
clk at splash.princeton.edu
Sun Dec 9 09:07:00 AEST 1990
I have an EXAbyte 8200 external drive (SCSI) on a 4/490 (SunOS 4.0.3) and
I have a couple of questions.
Does anybody know what parameters to give to dd to get the Exabyte drive
to act like a streaming device? I'm trying to maximize the data transfer
rate and minimize the time it takes to write/read a file.
I've done some experiments with an 8 MB file and the data is not easy to
interpret. Here are some examples:
time dd if=ps.a.tar of=/dev/nrst1 bs=10k
783+1 records in
783+1 records out
0.0u 3.4s 1:23 4% 0+208k 983+1io 980pf+0w
time dd if=ps.a.tar of=/dev/nrst1 bs=20k
391+1 records in
391+1 records out
0.0u 1.8s 1:24 2% 0+208k 2+1io 0pf+0w
time dd if=ps.a.tar of=/dev/nrst1 bs=100k
78+1 records in
78+1 records out
0.0u 1.0s 1:21 1% 0+296k 2+0io 0pf+0w
time dd if=ps.a.tar of=/dev/nrst1 bs=246k
31+1 records in
31+1 records out
0.0u 1.1s 1:33 1% 0+416k 2+1io 0pf+0w
The documentation gives the following information:
- physical block size is 1K
- data buffer consists of 256 KBytes of DRAM
- maximum burst data transfer rate does not exceed 1.5 MBytes/sec
- typical performance is expected to be 1.2 MBytes/sec
- sustained transfer rate of 246 KBytes/sec
Why the difference between the "typical performance" rate and the
"sustained transfer" rate? Which should I expect to see? How can I
measure this? If I use the data above from time, which time do I use, user
cpu seconds or elapsed time? Niether seemed to give the documented
transfer rate. What am I doing wrong?
If anyone could shed some light on this mystery I would be very grateful.
Thanks.
Christopher L. Kranz GFDL
Internet Address: clk at gfdl.princeton.edu Commercial: (609)452-6585
UUCP Address: princeton!gfdl!clk FTS: 298-6585
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