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Tivoli Storage Manager

Posted on 2013-05-30
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Last Modified: 2016-07-05
When I do a "q vol" in tsm it lists estimated capacity any where from 1.2T to 4.6T for my LTO5 tape volumes.  Two questions - 1st Since all tape volumes are LTO5 why are they not all the same estimated capacity? 2nd I do not have compression set in the client dsm.opt file, so is my TSM server defaulting to compression=yes?
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Question by:749er
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6 Comments
 

Author Comment

by:749er
ID: 39209396
Forgot to include this TSM version 6.3.2.200
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max_the_king earned 2000 total points
ID: 39210294
Hi,

your questions:

1) when volumes are in "filling" state, TSM server can not possibly know which kind of data will get to the volume (even if you do not have compression on TSM client, an application may kind of compress data when is called by a backup application); so TSM server will calculate the amount of the real data it already holds, and do an average on what it is expected to receive on the next data to come. The sum of those 2 numbers gives you the estimation by TSM. You may as well set the Estimate capacity parameter into devclass definition, but I believe there's no use in doing it.

2) TSM is not deafulating to compress, although you may set compression on the device class (see define device class command - the format parameter defaults to 'DRIVE' but you can force it, for example, to ULTRIUM5c, which mean LTO5 compressed)

here is a general explanation i found on an old book of mine:

Tape Volume Capacity and Data Compression

How TSM views the capacity of the volume where the data is stored depends on whether files are compressed by the TSM client or by the storage device. It may wrongly appear that you are not getting the full use of the capacity of your tapes, for the following reasons:

    A tape device manufacturer often reports the capacity of a tape based on an assumption of compression by the device. If a client compresses a file before it is sent, the device may not be able to compress it any further before storing it.
    TSM records the size of a file as it goes to a storage pool. If the client compresses the file, TSM records this smaller size in the database. If the drive compresses the file, TSM is not aware of this compression.

hope this helps
max
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Author Comment

by:749er
ID: 39211201
Max,

Thank you for taking time to post an answer to my question. Your explanation and the information you provided was a great help. Again thank you!!!!!!!!
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Expert Comment

by:max_the_king
ID: 41692124
Hi,
it seems the author really liked my solution and just forgot (or didn't know) how to assign points ...
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