DDS5 Capacity

Posted on 2006-05-08
Last Modified: 2007-12-19
Hi All,

I have a DDS5 DAT72 tape driver, one would assume that with compression I would be able to back up 72GB of data.

I remember however, that DDS4 did not back up the full 40GB.

What can i realistically expect the tape drive to back up?

Question by:gareth629
    LVL 47

    Assisted Solution

    36 Gb without compression and that's realistic

    You only get 72 Gb if you get 2:1 compression and this is only possible if the data can be compressed by 2 to 1.

    Complex binary files like jpegs will not compress 2:1
    Database files will probably compress better than 2:1

    The answer really depends on the data you are trying to back up.  If you didn't get 40 Gb with DDS4 and your data composition is still the same then you won't get 72 B with DDS5.
    LVL 47

    Expert Comment

    That's 72 Gb and not 72 B.
    LVL 32

    Accepted Solution

    The KEY speci here is "UP TO 72GB".  The "native" capacity of these tapes is 50% of the advertised capacity.  So a DAT72 will hold only 36GB for sure.  

    The drive incorporates a compression scheme to attempt to achieve the listed 72GB figure.  The problem is that some data cannot be compressed.  Usually this is because it's already compressed.  ZIP, JPG, MPEG, MP3, and similar files are already stored in a compressed form and will NOT compress any further.  

    So depending on your mix of file types, your true capacity will vary, as much as 2:1.

    Author Comment

    Thanks guys,

    mostly database backup and word docs, so i am looking good for a good amount?

    LVL 47

    Expert Comment

    Both those types usually compress well but you won't know for certain until you try the backup utility.

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