Brian Anderson <[EMAIL PROTECTED]> wrote:
>Hardware compression... How can I tell if it's enabled / disabled /
>working correctly.
I don't know of anyway to tell, unless there's some hardware diagnostics
that came with the tape drive. (Which probably won't run under Linux
anyhow.) I'd say that unless the tape drive manual mentions hardware
compression, the tape drive probably doesn't have it.
>I got a tape drive from a friend. It is listed as being a 12/24 gig DAT. I
>am currently only getting 12 gig of data on it. Currently I'm backing up
>with a simple tar script...
If it's an HP DAT24 12Gb is native, 24Gb compressed, although I don't know
*anyone* who'se ever gotten 2:1 compression. I average about 50 - 65%.
>I know very little about tape drives (any good FAQ would be welcome). I'm
>assuming that the data type is still relevant, even with hardware
>compression? (an mpeg file won't compress as much as a text file...)
Your assumption is correct.
>Essentially, I'm looking at backing up a lot of highly compressed data. My
>assumption is that I can expect that I really won't get that dreamt of 2:1
>ratio on the tape label... I'd just like to get confirmation on that.
You could use software compression (The -z switch will tell tar to use gzip
or use -Z for compress), which will probably slow down the backup and won't
help anyway with files that either (a) are already "pre-compressed" or (b)
won't compress much. In fact, depending on the type of the file, the
"compressed" version may be larger than the original.
>Assuming my data is compressed to begin with, I'm only going to get 12 gig
>on this, right?
Roughly, although this is still a lot of data. Remember that anytime
you're writing to tape it's done in tape blocks so there may be some
"empty" space at the end of a tape block, especially if you're writing a
lot of small files.
-Eric
Eric Sisler
Library Computer Technician
Westminster Public Library
Westminster, CO, USA
[EMAIL PROTECTED]
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