97 lines
4.5 KiB
Smalltalk
97 lines
4.5 KiB
Smalltalk
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From leland@wacky.acet.org Mon Nov 22 17:48:45 1993
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Received: from mwunix.mitre.org by chsun.eunet.ch (8.6.4/1.34)
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id RAA09132; Mon, 22 Nov 1993 17:48:41 +0100
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Received: from wacky.acet.org.acet.org ([192.188.104.18]) by mwunix.mitre.org (5.65c/SMI-2.2)
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id AA13343; Mon, 22 Nov 1993 11:46:42 -0500
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Received: by wacky.acet.org.acet.org (4.1/SMI-4.1)
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id AA06945; Sun, 21 Nov 93 16:30:44 EST
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Date: Sun, 21 Nov 93 16:30:44 EST
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From: leland@wacky.acet.org (Robert Leland - PSI)
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Message-Id: <9311212130.AA06945@wacky.acet.org.acet.org>
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To: mw@chsun
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Subject: SCSI tape driver.
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Cc: leland@wacky.acet.org
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Status: OR
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I would like to change the way scsi tape /dev/rst maps the minor device.
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This will allow for the selection of more than just one density of tape.
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Also though my Archive Viper 2525 drive can Read QIC-24 Tapes generated by
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a sun tape drive, it has to do this by traversing the tape several times
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until it figures it is a QIC-24, I would rather not wear out my tapes!
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This change would allow all type drive types to specify 3 additional densities, other than
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the default.
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----------------------------- The Bottom Line(first)------------------------------
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People currently using
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/dev/rst0, rts1 .... rst15
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would remain uneffected, regardless of tape drive type.
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People using the Exabyte type tape drives including Python that normally use
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/dev/rst16 , /dev/rst32
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would use instead:
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/dev/rst32, /dev/rst64
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(See below for more details)
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-------------------------------------------------------------------------------------
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Current
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* Specific to Exabyte:
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* minor bit 4 [b1bbbb] (aka /dev/rst16) selects short filemarks
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* Specific to 8mm Drives.
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* minor bit 5 [1bbbbb] (aka /dev/rst32) selects fix block mode, 1k blocks.
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*
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Minor Device: --------------------------------+
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| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
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+---+---+---+---+---+---+---+---+
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^ ^ ^ ^ ^ ^ ^ ^
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| | | | | | |___|_____ Unit Number
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| | | | | |_____________ NoRewind
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| | | | |_________________ HiDensity
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| | | |_____________________ Short FileMarks
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|_________________________ Fix block mode 1K
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- - - - - - - - - - - - - - - - - - - - - - -
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Proposed
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* Specific to Exabyte:
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* minor bit 5 [bb1bbbbb] (aka /dev/rst32) selects short filemarks
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* Specific to 8mm Drives.
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* minor bit 6 [bb1bbbbb] (aka /dev/rst64) selects fix block mode, 1k blocks.
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Minor Device: --------------------------------+
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| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
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+---+---+---+---+---+---+---+---+
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^ ^ ^ ^ ^ ^ ^ ^
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| | | | | | |___|_____ Unit Number
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| | | | | |_____________ NoRewind
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| | | |___|_________________ HiDensity
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| |_________________________ Short FileMarks
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|_____________________________ Fix block mode 1K
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Advantages: More similar to sun mapping, Keeps bits together.
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Disadvantages: Possiblely some initial confusion.
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- - - - - - - - - - - - - - - - - - - - - - -
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Alternate Proposed
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I would rather keep the density bits together but we could...
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Split the bits used for density Use bits 3 and 6:
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Minor Device: --------------------------------+
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| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
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+---+---+---+---+---+---+---+---+
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^ ^ ^ ^ ^ ^ ^ ^
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| | | | | | |___|_____ Unit Number
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| | | | | |_____________ NoRewind
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| | | | |___________________________________ HiDensity
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| | | |_____________________ Short FileMarks |
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| |_________________________ Fix block mode 1K |
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|_________________________________________________|
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This would mean that other users would remain uneffected.
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-----------------------------------------------------------------------------------------
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This change will also benefit other tape drives, so that specific densities can be specified.
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Could really use three bits for density, however It's nice to have a spare bit for the future.
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-Rob
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