Subject: Re: RAW access to files
To: None <email@example.com>
From: David Laight <David.Laight@btinternet.com>
Date: 12/12/2001 22:12:42
> Was there some reason to not use a second process? I once got fed up
> with the way dd between two disks kept each disk busy only about half
> the time and built a program that had a reader process and a writer
> process, with blocks passed between them via shared memory (mmap
> MAP_ANON|MAP_SHARED, fork, and you have shared memory that doesn't
> stick around on exit the way a SV SHM segment does). It helped; even
> between two disks on the same SCSI chain, I saw significant overlap
> (based on watching the disk lights).
Wrote a similar beast (tc) for this:
% find . -print | cpio -oc | tc > /dev/rmt0
To get QIC150 tape drives to stream...
provided the writing task (the one with a char special fd) was set
real-time you could detect the tape turn around, even going through
the terminfo database.