On Fri, Mar 17, 2006 at 12:00:04PM -0500, Salada, Duncan S (Titan) @ TITAN
wrote:
> Hello,
>
> I'm having trouble getting amtapetype to give me a 200gb tapetype for a HP
> Ultrium LTO 1 drive. It tells me that hardware compression is on, and I've
> tried using "-e200g" with "-f/dev/rmt/0ubn" and "-f/dev/rmt/0cbn" in
> desperation. But it still will only give me the 100gb tapetype:
>
> define tapetype Ultrium_I-HP_C7145_233S {
> comment "just produced by tapetype prog (hardware compression on)"
> length 100864 mbytes
> filemark 0 kbytes
> speed 14228 kps
> }
>
> I'm using amanda-2.4.5p1 on Solaris 10. I've searched around for a while but
> I've found nothing. Any hints/explanations would be greatly appreciated.
>
The tape can physically hold only so many bytes. This is called
its "native" capacity. For Ultrium/LTO 1 that is 100GB. That
is what tapetype determines so it is correct.
Then there is compression. Most tape manufacturers think their
hardware compressor will shrink your data to 50% of its original
size. Thus a pair of 200GB of data will shrink to 100GB on tape.
Sony believes their AIT compressor does a better job and claims
it will shrink your data to 38% of the original size.
But different types of data compress to different degrees. It
can range from not at all to over 90% compressibility. How
much will your actual data compress? Who the heck knows?
If you want to leave the drive to compress your data you will
have to guess (nah estimate, Nah its just a guess until you
have some runs under your belt) how much your data compresses.
Then up the tape size with an editor. If you have all text,
it might compress to 1/3 the original size, so the capacity
could be 300GB. If it is a lot of software and video and
audio and databases, it wont compress much; set the size to
130-160GB.
Alternatively let your computer(s) do the compressing before
sending it to the tape drive. Then amanda can be told it can
send 100GB of that already compressed data to the drive.
--
Jon H. LaBadie jon AT jgcomp DOT com
JG Computing
4455 Province Line Road (609) 252-0159
Princeton, NJ 08540-4322 (609) 683-7220 (fax)
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