Date: Tue, 5 Oct 1999 22:50:41 -0700 (MST) From: John and Jennifer Reynolds <jreynold@primenet.com> To: mjacob@feral.com Subject: Re: questions on observed tape navigation behavior Message-ID: <14330.58161.440372.617607@localhost.primenet.com> In-Reply-To: <Pine.BSF.4.10.9910052231130.57745-100000@beppo.feral.com> References: <14330.52789.99569.326161@localhost.primenet.com> <Pine.BSF.4.10.9910052231130.57745-100000@beppo.feral.com>
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[ On Tuesday, October 5, Matthew Jacob wrote: ] > > Nope. You're confused over the 'sf' part of Bsf and Fsf. It is 'space > filemark'- not 'space file'. > > So, after step 5 you would be: > > and after step 8 you would be: > > Sun used to confuse the semantics of this a bit- they invented a > "Backspace File" function. This is hard to implement in hardware since > tape drives typically note when a fileMARK (or a setMARK) has passed- not > datablocks. Aaaa ... then that would explain it. The behavior I was "used to" was based upon doing dumps long ago as a sysadmin of a SunOS 4.1.3 box in school. Your explaination of what FreeBSD is doing make sense. I just wanted to make sure that what I was seeing was in fact "reality." > So, if you want to backspace *files*, the formula is: > > back_space_file(N Files) = mt bsf (N + 1), mt fsf 1 > > Naturally this has a problem if you're only N files into the tape, so > watch out for errors. If you get any error with this, assume you don't > know where the hell you are and rewind. OK. > Also- as a side note- don't be alarmed if 'hardware' block numbers differ > by more than one over filemarks, or even block to block. You cannot assume > that they are densely packed as they are what the *drive* finds most > convenient for locating to a specific spot on the tape. OK. Thanks! -Jr -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= John Reynolds Chandler Capabilities Engineering, CDS, Intel Corporation jreynold@sedona.ch.intel.com My opinions are mine, not Intel's. Running jreynold@primenet.com FreeBSD 3.3-STABLE. FreeBSD: The Power to Serve. http://www.primenet.com/~jreynold/ Come join us!!! @ http://www.FreeBSD.org/ =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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