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Compressed data size to an LTO-3 Tape

Compressed data size to an LTO-3 Tape

Compressed data size to an LTO-3 Tape

This is referenecing an old thread. thread1203-1379600: Tape not compressing data as expected...
I was reviewing my backups to find out if I can reduce the number of tapes being used.  The total weekend backup is 759Gb going to tape.  I always thought that these tapes can hold 800Gb of compressed data.  It seems that I get about 626Gb of data per tape.
I have an Aux copy of our email data base that goes to tape on the weekend and its also the same size. That too gets 625Gb on 1 tape and the remainder on the second one.
My question is, is this normal?


RE: Compressed data size to an LTO-3 Tape

It's not uncommon to get less than a full 2:1 compression ratio on tape, however, I wonder if the issue here is related to Commvault possibly using the "Total Job Size" to indicate the amount of data that been copied to the tape, as opposed to using the "Size on Media" figure which I assume may also include backup meta data and index information?

I may be way off, but if I get time I will have a play around - if you are interested in also checking it out, here's what I plan to do:

Browse to Policies, Storage Polices, and select the appropriate Storage Policy.
Within the left hand pane, right click on the Auxiliary copy, select View, and select Jobs.

Now within the Job Filter Dialog, I will adjust the Start Time and Finish Time Filters so that capture all jobs within the Auxiliary Copy window, and press OK.

I will now see a list of the jobs that have been Auxiliary Copied, and within all the information there are 2 columns, "Size on Media" and "Total Job Size".  I will add these columns individually, and check which column is closer to the Transferred figure.

RE: Compressed data size to an LTO-3 Tape

It's normal as 800gb assumes 2:1 compression but if you're backing up data that is already highly compressed such as JPG/Video/Office Documents containing photos you're going to see much less compression than if you were backing up text files which are highly compressible.

RE: Compressed data size to an LTO-3 Tape

I've actually gotten better that 2 to 1 on some tapes.   

RE: Compressed data size to an LTO-3 Tape

> I've actually gotten better that 2 to 1 on some tapes.

It might be more accurate to state "with some data" rather than "on some tapes", since the compression is more a function of the data being compressed than the media it is ending up on. Still, I know what you mean!

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