Getting 22 GB instead of 40 with DDS4 tapes - Veritas Backup Exec

This is a discussion on Getting 22 GB instead of 40 with DDS4 tapes - Veritas Backup Exec ; I am using an HP Surestore DAT 40x6 tape drive which uses DDS4 tapes to perform backups using Backup Exec V. 7.3 (rev 2371, NT4 SP6 environment). The tapes have a capacity of 40 GB however during backups, each tape ...

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Thread: Getting 22 GB instead of 40 with DDS4 tapes

  1. Getting 22 GB instead of 40 with DDS4 tapes


    I am using an HP Surestore DAT 40x6 tape drive which uses DDS4 tapes to perform
    backups using Backup Exec V. 7.3 (rev 2371, NT4 SP6 environment). The tapes
    have a capacity of 40 GB however during backups, each tape only backs up
    around 22 GB of data. I have set up compression preference (under options)
    to "use hardware if available, otherwise use software".
    Is there another setting in the software that I need to know about in order
    to get the full 40 GB capacity? Please help. Thanks.

    Jim

  2. Re: Getting 22 GB instead of 40 with DDS4 tapes

    20/40 is a marketing term meaning 20GB uncompressed, 40GB compressed at
    at 2:1 ratio (Something rarely acheived in the real world. Depending on
    your data type(s) you may get as high a 4-5:1, or as low as 1.1-1.2:1

    22GB is about 1.2:1 a little low, but not really anything to get overly
    alarmed about

    Jim wrote:
    >
    > I am using an HP Surestore DAT 40x6 tape drive which uses DDS4 tapes to perform
    > backups using Backup Exec V. 7.3 (rev 2371, NT4 SP6 environment). The tapes
    > have a capacity of 40 GB however during backups, each tape only backs up
    > around 22 GB of data. I have set up compression preference (under options)
    > to "use hardware if available, otherwise use software".
    > Is there another setting in the software that I need to know about in order
    > to get the full 40 GB capacity? Please help. Thanks.
    >
    > Jim


  3. Re: Getting 22 GB instead of 40 with DDS4 tapes

    On 5 Jan 2001 14:16:38 -0500, "Jim" wrote:

    >
    >I am using an HP Surestore DAT 40x6 tape drive which uses DDS4 tapes to perform
    >backups using Backup Exec V. 7.3 (rev 2371, NT4 SP6 environment). The tapes
    >have a capacity of 40 GB however during backups, each tape only backs up
    >around 22 GB of data. I have set up compression preference (under options)
    >to "use hardware if available, otherwise use software".
    >Is there another setting in the software that I need to know about in order
    >to get the full 40 GB capacity? Please help. Thanks.
    >
    >Jim


    On my last backups I got 1.2-1.5-2.1-1.2 : 1 compression. I am using
    BENT 7.3 and a DDS2 tape unit in a similar environment. I am using
    software compression because of compatibility issues.

    I am pretty certain that the capacity of the tapes with compression
    will vary as much as this on large datasets, especially if there are a
    lot of compact files like jpg images and the like. They do not
    compress at all. Quite normal I would say.

    Of course you may have an issue with the sales hype, but the fine
    print says that compression may vary depending on contents....



    Bo Berglund
    bo.berglund@telia.com

  4. Re: Getting 22 GB instead of 40 with DDS4 tapes


    Up until a month ago I got ~37 Gb per tape. Now I get ~23 Gb on the same
    tapes (both amounts/tape very consistent). I have not yet found out why
    (compression is checked on my backups). I'm still investigating, but you
    probably don't have to live with 22Gb/tape backups.

    Gordon

    bo.berglund@telia.com (Bo Berglund) wrote:
    >On 5 Jan 2001 14:16:38 -0500, "Jim" wrote:
    >
    >>
    >>I am using an HP Surestore DAT 40x6 tape drive which uses DDS4 tapes to

    perform
    >>backups using Backup Exec V. 7.3 (rev 2371, NT4 SP6 environment). The tapes
    >>have a capacity of 40 GB however during backups, each tape only backs

    up
    >>around 22 GB of data. I have set up compression preference (under options)
    >>to "use hardware if available, otherwise use software".
    >>Is there another setting in the software that I need to know about in order
    >>to get the full 40 GB capacity? Please help. Thanks.
    >>
    >>Jim

    >
    >On my last backups I got 1.2-1.5-2.1-1.2 : 1 compression. I am using
    >BENT 7.3 and a DDS2 tape unit in a similar environment. I am using
    >software compression because of compatibility issues.
    >
    >I am pretty certain that the capacity of the tapes with compression
    >will vary as much as this on large datasets, especially if there are a
    >lot of compact files like jpg images and the like. They do not
    >compress at all. Quite normal I would say.
    >
    >Of course you may have an issue with the sales hype, but the fine
    >print says that compression may vary depending on contents....
    >
    >
    >
    >Bo Berglund
    >bo.berglund@telia.com



  5. Re: Getting 22 GB instead of 40 with DDS4 tapes


    I found that I had not been purging a daily compressed db backup onto a large
    disk. Noticed the disk was near 80%, purged compressed backups, now the
    backups are fine. My bad.

    I feel much better now.

    "Gordon McKinnon" wrote:
    >
    >Up until a month ago I got ~37 Gb per tape. Now I get ~23 Gb on the same
    >tapes (both amounts/tape very consistent). I have not yet found out why
    >(compression is checked on my backups). I'm still investigating, but you
    >probably don't have to live with 22Gb/tape backups.
    >
    >Gordon



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