marr@cup.portal.com (scott andrew marr) (10/20/90)
I have for the last several months trying to get data off of an Exabyte 8mm tape drive at a resonable rate. People from this group and from DEC told me to use the nbuf ioctl calls. I did try them, but got no noticable improvement in I/O. No one at DEC had an answer as to why. I finally ended up using dd and piping the data into my process. This seemed to work, for a while. Then we found that on some tapes the I/O would start out fast and then slow down after a few hundred Mbytes. When the system slows down you can hear the tape transport turning off and on. Does anyone have experience with using nbuf on an Exabyte? What about any advice about buffer architecture or the number of buffers to use? Does anyone have any ideas why dd slows down? Any help would be appreciated, I have a physicist who is getting quit upset when his data dumps take 12 hours. He's starting to say things like "Why don't you just write your own device driver?" ------------------------------------------------------------------------------- Scott Marr marr@cup.portal.com -------------------------------------------------------------------------------