From: Tim Chipman (chipman@ecopiabio.com)
Date: Fri Jun 18 2004 - 10:01:00 EDT
Hi all,
a question driving me up the wall, which I suspect others have already
gone around the bend to resolve. Hence I hope to gain from their
experience :-) (and alas, this is not clearly answered in google,
archives,etc).
Assuming that I've got a large pile of data to backup to tape, ie:
-approximately 160gigs of pre-compressed .BZ2 files (generated by
"bzip2", a very efficient file compressor...)
- a SDLT tape drive which claims to store "160gigs raw / 320gigs
compressed"
-optional: Netbackup 4.5 available to do the job if desired.
Otherwise, tar / gnu-tar, usual filesystem commands...
The first attempt at this, simply was to use netbackup and push data to
the tape. Alas, after 144gigs it told me "tape full" (also, "job failed,
start over")
arrgh!
Bit more thought, a few questions, it has been suggested to me that (1)
160gigs of tape is really same as "160 gigs of new hard drive", ie,
base-10 vs base-2 issues result in the "160 gig" actually ... being
smaller than 160 gigs. This accounts for ~ 2% less storage than expected
roughly {since "1k= 1024 vs 1000", difference of ~2%}. (2)
Pre-compressed data may actually expand when netbackup tries to compress
it further. (3) Pre-compressed data may expand further still if
HW-compression is enabled on the tape-drive. (4) Generally, the universe
states that you never get quite what you want or expect? :-)
[ Umm. Yes. I guess that 4th item isn't totally relevant. ] So after
my first attempt, I'm wondering if there is some better possible
approach to get this data dumped to tape to optimize the actual storage
volume a bit better. I'm not expecting to get more than ~155gigs of
(densely pre-compressed) data onto a 160gig tape in a case like this,
since .. that's all the stoarge space there *really* is there, but ...
144gigs seems a bit lame when 155gigs is ?theoretically? possible.
Note, this data store isn't changing often / needing
additions/removal/etc.. so my concerns about data management are
minimal. Of course, IF there was a way to do this inside netbackup,
that would be nice, but (of course) it isn't exactly straightforward in
NBU to say, "no HW or SW compression".
If anyone has ever resolved an issue like this (even if on smaller
media, context, etc) in the past ... I'd certainly be very happy to hear
any thoughts.
Thanks!
--Tim Chipman
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