"Native" is the actual amount of data that the tape can theoretically store,
before compression. A 12.0 Gig file should fit on a 12.0 Gig capacity tape.
Suppose you are able to take a 16.0 Gig file and compress it down (using
PKZIP or whatever) to 12.0 Gigs. Now that 16.0 Gig file can fit on the 12.0
Gig tape.
Usually, the tape drive has built-in compression. In this case, the tape
drive may receive 16 Gigs of data from the server during a backup, but the
tape drive compresses the data just before it writes it to tape. The
compressed data uses less tape space, and more data can fit on the tape.
Often, you'll see tape drive and tape media capacities quoted as double
their native capacities. They are assuming that the data being written to
tape is well-compressible (after compression the data is 1/2 its original
size).
In the instance of DDS3, it often is stated that it is a 24 Gig drive, when
in fact, it is a 12 Gig drive with a potential of storing up to 24 Gigs
after the data is compressed (assuming a 2:1 compression ratio).
Hope this helps.
Brad.
-----Original Message-----
From: matt holland [mailto:[EMAIL PROTECTED]]
Sent: Friday, October 20, 2000 1:30 PM
To: [EMAIL PROTECTED]
Subject: tape capacity
Hello,
I'm new to this list and subscribed because I have a question I hope one of
you will be able to answer for me.
I'm using Retrospect 4.2 for Mac, backing up a total of three Mac Servers to
an APS DAT drive. The tapes I use are Sony DDS3 125P which state a Native
(I'm not sure what Native means) capacity of 12.0 GB.
After looking at the log of how much data is being backed up, it added up to
14.3 GB. How can this be? It seems that the tape shouldn't be able to handle
it but I receive no errors.
Any explanations? Suggestions?
thank you,
-matt
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