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Date:      Sat, 19 May 2007 18:39:39 -0500
From:      Dan Nelson <dnelson@allantgroup.com>
To:        jhall@vandaliamo.net
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Tape Capacity Used?
Message-ID:  <20070519233939.GA13345@dan.emsphone.com>
In-Reply-To: <1757.65.117.48.155.1179578635.squirrel@admintool.trueband.net>
References:  <1757.65.117.48.155.1179578635.squirrel@admintool.trueband.net>

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In the last episode (May 19), jhall@vandaliamo.net said:
> I am trying to calculate how much of the space on my tape has been used.
> 
> This is what I have done, and I want to make sure I barking up the
> right tree before going too far.
> 
> Move the tape to the end of the data. (mt eod).
> 
> Find the logical block location of the drive (mt rdspos).
> 
> /dev/nsa0: logical block location 2242573
> 
> If I multiply the result (2242573) by my blocksize, does this give me
> the total amount of the tape that has been used?

If your tape drive has hardware compression turned off, that should be
accurate.  With compression enabled, logical blocks can be varying size
on tape depening on the compression ratio.  If your device supports the
"rdhpos" command, that might give you a number that more accurately
indicates where on the physical tape you are.  It's a "device-specific
value", though, which may not translate to a sequential "0-max" range.

-- 
	Dan Nelson
	dnelson@allantgroup.com



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