From: utzoo!decvax!harpo!seismo!hao!menlo70!sytek!zehntel!zinfandel!hickman Newsgroups: net.unix-wizards Title: Re: disk block interleave methods - (nf) Article-I.D.: zehntel.740 Posted: Thu Feb 10 13:20:04 1983 Received: Sat Feb 12 07:01:27 1983 #R:tekmdp:-175400:zinfandel:12400014:000:1191 zinfandel!hickman Feb 10 08:54:00 1983 You seem to be confusing the several types of interleaving available: 1) Disk format interleaving: - When the disk pack is formatted, an interleave is specified which allows the controller to get sequential multiple sector reads in the same rotation (i.e., no rotational loss because the controller couldn't finish dealing with the first sector before the second sector passed under the disk heads) 2) Unix filesystem interleaving: - on top of the normal (and hopefully transparent) disk interleaving, unix allows a filesystem interleave which is valid only at the time of a "mkfs". Once the filesystem has been used, blocks tend to be moved around alot, and the interleave gets lost. This is done so that files which don't move, will be accessable to unix without rotational delays. Unix attempts read ahead, and thus the filesystem rotational interleave should be set for whatever time is needed to send the first request to the driver and compute the read ahead request. Unfortunately, the filesystem interleave has little if no effect on most unix systems (4.1, 4.2 are exceptions). Hope this brings things into focus... kipp hickman