[Gllug] [bit OT] what block size is best for a tape drive?

[t.clarke]

re tape drives

My experience with Unix at any rate is that tape derives need a block size of
at least 10k to work efficiently.  If you 'tar' a directory to a tape drive
with a small block size you may well see (at least on my version of Unix !)
that the tape drive does not run continuously, but stops and starts.
On a DAT drive at least this slows down things incredibly,  as the drive has
to back up and re-position every time it stops and re-starts.
With a larger block size the drive should 'stream' (run continously) and thus
achive best backup speed.

I have never used the hardware compression on the drives,  as I believe
the feature requires suitable software (not available on my machine) to
write the necessary command(s) to the drive.  As far as I am aware the drive
runs at the same physical speed whether compression is on or off; compression
is simply done on the fly and results in more data being written to a given
block of tape.

The quoted compression rates for drives are highly dependent on the data you
are writing.  IF your writing data thats already compressed with gzip/bzip
or is inherently compressed like jpegs, hardware compression will most likely
do nothing for you  - indeed I have heard say iy might actually slow things
down!   Of course the other problem with hardware compression is that you
can't (I assume) read the tape with another make of drive?

Tim
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