Hello all!

I don't think either type of compression produces good results for DRM
backup images.

The ADSM DRM client backs up a disk image sector by sector, as it does not
"know" how to interpret partition information to determine unused storage
areas.

And, while certain file types show certain "patterns" of byte sequences
(which allow good compression ratios), data belonging to various files (of
different file types) and unused storage areas (which usually contain
random data, i.e. the data that were written to them before the storage
area was released) are usually mixed up on the disk; and it is this mix of
usage types that usually prevents good compression ratios for *any* type of
compression schema.

HTH - Alfred Novacek


>There are very good reasons to do compression in software on the client.
>Fundamentally it is a tradeoff between ADSM client CPU cycles and I/O ops on
>ADSM client, intervening network, and ADSM server.  Your priorities and
>circumstances will dictate your solution.
>
[...]
>
>P.S. wrt the drive images of ADSM DR for Intel IDE hard drives, it is very
>possible that the image is very compressible; however, those backups are
>'cold' wrt O/S being up so downtime to compress may become an overriding
>factor.
>
[...]
>
>> Hardware compression would be your best bet.
>>
[...]
>>
>> If we use DRM for our Windows NT machines the size of the image backed
>> up on our server is the same size as the physical partition size of the
>> disk. I
>> understand that this is normal but isn't there the possibility to use
>> compression
>> because we have other disks which have 20Gbytes on which only 2Gbytes
>> are useable.
>>
[...]

------------------------------------------------------------------------
Dipl.-Ing. Alfred Novacek
Dipl.-Ing. Alfred Novacek
Institute for Data Processing in Business Administrations,
     Economics and Social Sciences
Johannes Kepler University Linz / Austria
E-Mail: Novacek AT idv.uni-linz.ac DOT at
        Novacek AT pop.idv.uni-linz.ac DOT at
WWW: http://www.idv.uni-linz.ac.at