I was asked by a couple people to provide a summary. Sorry it's late.
Original Question: "What is the Maximum capacity of the TLZ06 tape drive?"
I received many replies that suggested I use the rmt<n>h or rmt<n>m device.
I'll list ONLY a few ...
>From Dr. Thomas P. Blinn.
See the tz and mtio reference pages. As you'll find documented there, when
you use the rmt<n>h or rmt<n>m device name (or the no-rewind version),
you'll get compression turned on on the TLZ06. So, do your dump to, e.g.,
/dev/rmt0h and you'll get "high density" support.
>From Alan Rollow
The question you're really asking is "What is the maximum compress
ratio"? And short of measuring how the drive compresses data with
the same value, you can't answer it. The wonderful thing about
compression is that it allows fitting more data on a tape than
when not using compression (usually). The problem, is that it
becomes very hard to measure tape usage. The compression ratio
varies with the data; some will compress a lot, some will compress
a little and some will actually get larger.
If your data will compress at 2:1 simply write to the high density
tape device. The driver knows to enable compression. If your
backup program can write to a pipe, you can estimate compression
by pipe the output to compress with the -v option. I think the
algorithms used are basically the same.
>From Robert McMillin
Use the /dev/n?rmt0h device to enable compression. The compression is
Lempel-Ziv, which means it's basically the same thing you get when you
use compress(1). If you're already using a compressing archiver, you
won't see any improvement. If, on the other hand, you're backing up a
lot of Oracle database files (for instance), which are mainly empty
space, you should see an ENORMOUS improvement. One correspondant to the
list recently wondered whether he was hallucinating because the Oracle
backups compressed so well. We have around 4 GB on our Oracle-based
systems, of which around 1 GB are Oracle data files. We archive these
easily on a single 90m DAT using the TLZ09 drive. (Incidentally, I highly
recommend the TLZ09 -- they're incredibly fast -- we do everything in
under an hour.)
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I should note that I always use the /dev/n?rmt0h device and was NEVER
able to get more than 2 GB on a tape when using the dump command. I was
successful at getting 4 GB by using the rdump command with the -C (Compress)
flag.
Received on Mon Oct 20 1997 - 16:53:52 NZDT