From: utzoo!decvax!genrad!mit-eddi!smh
Newsgroups: net.unix-wizards
Title: Re:  Flames on system backups / The software tool approach
Article-I.D.: mit-eddi.117
Posted: Sun Apr 17 11:56:35 1983
Received: Wed Apr 20 21:27:50 1983
References: sri-arpa.943

Chernikoff's exposition on using a filter to handle multi-reel
packing on tape backups seems pretty neat.  Of course, high-volume
pipes on small machines (PDP-11's) without huge buffer cache's
might slow down backups somewhat, but Chernikoff neglected to
mention what might be another BIG win:
	Tape backups on UNIX suffer because IO is synchronous.  Some
number of blocks of data is gathered into a buffer (typically 20 blocks)
and then the backup process waits while the tape drive does its thing.
Having a pipe between the disk-reading process and the tape-writing
process could provide desirable IO overlaps, and could significantly
increase throughput.  The tape blocksize might have to be tuned to
agree with pipe size.
	Has Dan or anyone had any experience with this?
				Steve Haflich
				MIT Experimental Music Studio
				...genrad!mit-eddie!smh