Date: Wed, 22 Mar 1995 09:12:31 +0100 (MET) From: J Wunsch <j@uriah.heep.sax.de> To: freebsd-hackers@FreeBSD.org (FreeBSD hackers) Subject: Re: Problems with 2940 and 950210snap Message-ID: <199503220812.JAA13786@uriah.heep.sax.de> In-Reply-To: <199503220015.AAA06755@genesis.tiac.net> from "Steve Gerakines" at Mar 22, 95 00:15:44 am
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As Steve Gerakines wrote: > > I do have some questions about what some correct magtape behaviors are, > so if someone familiar with wt and st would raise their hand I would > be grateful. :-) One concern I have is regarding tape length. It > looks like dump wants to calculate the tape length in advance to avoid > reaching end of media. QIC-40/80 tape drives have a variable number > of blocks, depending upon how many have been marked bad, so how would > I get a decent length? Is it a problem for dump to just fall off the > end of the tape? Dump will abort and offer you to re-do the current volume if it falls off the end of the medium. I found that even QIC cartridges sometimes do suffer from being ``a bit'' too short. I always do something like dump 0uBf 150000 /dev/rst0 usr for a QIC-150 tape, even though they actually should have more than 150000 KB (it should be 150 * 1024 KB). Perhaps this is the same forgery like the hard disk megabyte agenda, however. To make it short: telling dump to write some megabytes less than the tape might actually be does not harm, the waste is usually acceptable compared to the time needed to write the dump. I think even QIC-525 and QIC-1000 cartridges will vary in their actual capacity depending on the used block length, btw. It would be nice if the tape drivers could pass the `early EOF warning' to the controlling process, e.g. by a signal. I'm afraid this would make it incompatible to the rest of the world, however. -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ Never trust an operating system you don't have sources for. ;-)
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