OT:DAT remaining capacity response

[Gary Nichols]

Alan,

If noone on the PLUG list can help, I bet someone on the Sun list can.  

suns-at-home@net-kitchen.com

~Gary


On 03 Aug 2001 10:42:08 +0000, Alan Dayley wrote:
> 
> This is not directly Linux related but I am having a <bleep> of a time
> finding an answer.  All of you on this list a experienced in other things
> besides Linux and I hope to tap a knowledgable brain somewhere.  Respond
> off the list if you would like.
> 
> I tested a Seagate DAT drive to determine the way it calculates the
> remaining capactiy response to the Log Sense Page 0x31 command.  I have
> conflicting information from other sources about the answer I should expect.
> 
> Question
> --------
> Do SCSI DAT drives report remaining capacity as an ABSOLUTE value or a
> value RELATIVE to the current location?
> 
> Hypothetical example: Take a 2GB tape.  Write 1GB of data to the tape.
> Rewind the tape.  Ask for remaining capacity (Log Sense Page 0x31).  The
> ABSOLUTE value response would be 1GB (total - used = remaining).  The
> RELATIVE value response would report 2GB (total - position = remaining).
> Which is the industry standard?  Is the other calculation method ever used?
> 
> Test
> ----
> Using the Linux tar command, I wrote 10, 1.2MB backups to a tape.  This
> created 10, 1.2MB files on the tape.  I queried remaining capacity three
> times: 1)after the last write, 2)after a back space of 5 file marks and
> 3)after a rewind.
> 
> Results
> -------
> Operation          Remaining Capacity
> After last write   3,777,480 KB
> After back spaces  3,784,037 KB
> After rewind       3,795,909 KB
> 
> Total capacity of media: 3,795,909KB
> 
> Conclusion
> ----------
> The Seagate DAT tape drive reports remaining capacity RELATIVE to the
> current location.
> 
> The question remains: What do other manufacturer's drives report?  Should I
> trust the Seagate results as representative of all DAT drives?  Since Log
> Sense Page 0x31 is a vendor specific page, I am not sure I should trust a
> universal remaining capacity method of calculation.
> 
> I ask this question here because there is an amazing lack of information on
> the net about how DAT drives should or do operate.  Info or pointers to
> info on this subject would be greatly appreciated.
> 
> Alan
> 
> 
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