On Fri, 21 Nov 2008, Haberl, Max wrote:

> Hi Justin,
>
> as far as i understand you enabled the compression in the policy right ?
No, compression is handled by the tape drive in hardware.  The compression
in the policy that you are referring to is whats referred to as client-side
compression, the data is compressed on the client before it is 'shipped' to
the netbackup media server, this can actual reduce actual compression rates
on the media itself because its sending a somewhat pre-compressed file to the
drive which cannot be compressed as well as it could be if it were a regular
file.  You would only want to use that option to save on bandwidth or if you
are backing up a host on a slow link.

> If yes, the benefit of the drive internal compression is around 0 cause you 
> still write a compressed tar file on tape.
See above.

>
> That means that the visible size of "bpmedialist -m <TAPE>" is already the 
> compressed size.
That command will show you how much is written on the tape once full then you
can calcuate the ratio based on an LTO-3 tape being 400GiB.

>
> Cheers
> Max


Justin.

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