[H-GEN] Linux Backup

Jason Parker-Burlingham jasonp at uq.net.au
Fri May 9 00:29:31 EDT 2003


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Robert Kearey <mammal at optushome.com.au> writes:

> Robert Stanford wrote:
>> I was under the impression if the tape drive supported hardware
>> compression then dump used it by default?
> Hardware compression causes ricketts and scurvy. Just say No, mkay?

To elaborate somewhat about the software/hardware compression thingy:

* The "window" of a compression algorithm in hardware is usually only
  a few bytes wide, which translates to decreased compression rates.

* It's often rather slow for that reason, too, and your computer
  (usually) can work much harder and is much less busy than the
  electronics in the tape unit.  Why not get more bang for buck?
  Also, software compression will allow you to change algorithms
  later, or use algorithms better suited to the data you are backing
  up in any particular case.

* Some people don't like to use even software compression because they
  worry that an error on the tape will invalidate all the data in
  later blocks.  In my experience software compression allowed me to
  back up much more data than otherwise and never gave me a moment's
  trouble; surely if something is wrong with the media or the drive,
  then you're up the creek anyway?

* Whatever you do, *never* turn on hardware and software compression
  at the same time:  instead of compressing the data even more, the
  hardware compression will only make the data slightly LARGER than
  before.

jason
-- 
``Oooh!  A gingerbread house!  Hansel and Gretel are set for life!''

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