From owner-freebsd-scsi Tue Oct 5 22:49: 1 1999 Delivered-To: freebsd-scsi@freebsd.org Received: from localhost.primenet.com (206-132-49-158.nas-1.SCF.primenet.com [206.132.49.158]) by hub.freebsd.org (Postfix) with ESMTP id C805C15687 for ; Tue, 5 Oct 1999 22:48:36 -0700 (PDT) (envelope-from jreynold@primenet.com) Received: (from jreynold@localhost) by localhost.primenet.com (8.9.3/8.9.3) id WAA14346; Tue, 5 Oct 1999 22:50:41 -0700 (MST) (envelope-from jreynold@primenet.com) From: John and Jennifer Reynolds MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <14330.58161.440372.617607@localhost.primenet.com> Date: Tue, 5 Oct 1999 22:50:41 -0700 (MST) To: mjacob@feral.com Cc: John and Jennifer Reynolds , scsi@FreeBSD.ORG Subject: Re: questions on observed tape navigation behavior In-Reply-To: References: <14330.52789.99569.326161@localhost.primenet.com> X-Mailer: VM 6.73 under Emacs 20.3.1 Cc: Sender: owner-freebsd-scsi@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org [ 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