Charles,
The amount of data that fits on the tape depends on the data's
compressibility. Hardware and software compression algorithms work
generally by eliminating redundant data and making the storage more
efficient. Different types of data have widely different levels of
compressibility. Text files and any file with lots of 'empty' space
(long runs of repeating characters, such as nulls or spaces) will
compress very well. Binary data that looks almost random to the eye
won't compress much (if at all). Program executables are usually
somewhere in between. Files that have been previously compressed with
gzip or winzip usually won't compress at all, and may even expand
depending on how smart your compression algorithm is.
If you are using tapes that hold 35GB native, then you can usually
expect to get somewhere between 35-70 GB on a tape. But sometimes, you
may get even more. I've seen 120 GB fit on a 35 GB tape! It all
depends on your data.
John
Charles Bartels wrote:
> Date: Thu, 10 Aug 2000 12:50:55 -0700 (PDT)
> From: Charles Bartels <ceb AT move DOT com>
> To: veritas-bu AT mailman.eng.auburn DOT edu
> <p0432041fb5b865e486d8@[38.31.46.122]>
> <p04320421b5b867cdfb7d@[38.31.46.122]>
> Reply-To: charles AT move DOT com
> Subject: [Veritas-bu] NetBackup tape usage
>
> Hi,
>
> I'm running NetBackup with a tape jukebox. When I look at the media
> list I see the following:
>
> id rl images allocated last updated den kbytes restores
> vimages expiration last read <------- STATUS ------->
> -----------------------------------------------------------------------------
> DJR892 6 2 08/05/00 22:22: 08/05/00 22:22: dlt 12795420 0
> 2 02/07/01 21:22: N/A
>
> DJR894 0 26 07/28/00 22:06: 08/09/00 22:09: dlt 21761349 0
> 16 08/16/00 22:09: N/A
>
> DJR897 0 10 08/07/00 22:04: 08/09/00 22:16: dlt 2021326 0
> 10 08/16/00 22:16: N/A
>
> DJR899 6 2 08/05/00 22:08: 08/05/00 22:08: dlt 5051234 0
> 2 02/07/01 21:08: N/A
>
> DJR902 6 3 07/08/00 22:13: 08/05/00 22:22: dlt 44499604 0
> 3 02/07/01 21:22: N/A FULL
>
> DJR904 1 20 06/17/00 22:02: 07/29/00 22:18: dlt 30258822 1
> 4 08/12/00 22:18: 06/19/00 09:35:
>
> DJR908 1 18 06/17/00 22:02: 07/29/00 22:09: dlt 34380545 0
> 2 08/12/00 22:09: N/A
>
> DJR913 0 155 06/11/00 20:05: 08/07/00 22:04: dlt 89306394 0
> 11 08/14/00 22:04: N/A FULL
>
> DJR916 6 5 06/10/00 20:02: 08/05/00 22:08: dlt 35868415 0
> 5 02/07/01 21:08: N/A FULL
>
> DJR918 5 6 06/10/00 20:02: 08/05/00 22:08: dlt 13859639 0
> 6 11/06/00 21:08: N/A
>
> DJR920 6 3 06/10/00 20:12: 07/08/00 22:13: dlt 50211961 0
> 3 01/10/01 21:13: N/A FULL
>
> =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
>
> My question is about the "FULL" tapes. The amount of data on each
> tape varies quite a bit, from 89+ GB down to less than 36GB. Why the
> huge disparity?
>
> -C.
>
> -------------------------------------------------------------------------
> Charles Bartels <charles AT move DOT com>, Lead Systems Administrator
> Cendant Corporation / Move.Com @ San Francisco, CA, US
> -------------------------------------------------------------------------
>
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