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Size on Tape?

When go to restore and look at my media, the column that is supposed to tell me the size of the backup set has a question mark?  Why is this?  What I am really wanting to know is how much room I have left on my tape.  Its DLT 4000 using DLT tape IV.  I want to know what kind of compression ratio I am getting with the hardware compression.  I there a utility I can use to look at the tape and find this out?
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donnatronious
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donnatronious
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sirbountyCommented:
What software are you using for backups?
Typically you would need to inventory and catalog the tape to determine its contents and what size it is...

On some backup software - you can have the jobs you run append to tape and then fail if enough room is not available...
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donnatroniousAuthor Commented:
Whoops, I'm using NTBackup on win2k server.
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sirbountyCommented:
From my limited experience with NTBackup - I don't think you can gather this information properly from the software.
Consider it a trimmed down version of some of the more popular backup solutions provided by Veritas...
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donnatroniousAuthor Commented:
I was hoping for maybe a small utility to just show me how much room and what type of compression rate I am gettting thanks
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sirbountyCommented:
If I recall A DLT 4000 is a 20/40 drive, correct?
Also - I'm quite certain DLT IVs are 35/70.
But unfortunately, you won't get that with a 20/40GB drive...
The absolute maximum you will get is 40GB - but that's unlikely.
Depending on the type of files you're backing up, you should average about 1.4-1.6/1 compression ratio - meaning you're likely to get between 28-34GB of data on a single tape.  If you're backing up a lot of files that are already compressed, this ratio will decrease considerably.  

One more thing to add - and again, I don't know your situation, but this works in most environments...

If you're on a daily backup schedule - set the M-Th jobs to be differential only.  Then have the Friday job as a Full (normal).
So tonight's job would run and be a complete backup of everything.  Monday, you insert a new tape, different job definition (differential/append).
Monday only backs up the files that have changed since Friday's job completed.
Tuesday-Thursday - same thing - but still since Friday's job completed (so obviosly Thursday's job will back up more than Monday's).

In the event of a restore, you would need the full backup and then whatever the last day's backup was.
So, if you lose a file on Wednesday - you would need to restore it from Friday, then restore it from Tuesday's differential job...make sense?

Hope that helps..
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sirbountyCommented:
Well, thanx for the grade.
I don't really feel I helped much here though...


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