clk@splash.princeton.edu ( Chris Kranz) (12/09/90)
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@gfdl.princeton.edu Commercial: (609)452-6585 UUCP Address: princeton!gfdl!clk FTS: 298-6585