[H-GEN] Tape Drives

Jason Henry Parker jasonp at uq.net.au
Mon Jan 7 17:41:59 EST 2002


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James Lever <jamver at adams.humbug.org.au> writes:

> Regarding compression turning on/off, it doesn't appear to have been
> mentioned, but for those who aren't in the business of working with tapes
> to turn it on/off is strictly dependant on whether you're writing to the
> correct device file.

Not always.  Linux, for example, has an ioctl (I assume it's an ioctl)
which you send to the device to turn on or off hardware compression,
but you still talk to /dev/nst0.

> this can easily be deteremined by looking up the tape driver man
> page on your system of choice (via man mt as it's different under
> each OS).

This is certainly true.

> Oh, and personally, if you really wanted to do a large scale local gzip of
> your data in a pipeline while backing up, it's very worthwhile making sure
> you have a large buffer ahead of the gzip to keep data streaming nicely to
> the tape drive.

I'm having a devil of a time getting better than 700kB/s to my DDS3
drive.  This may help.

> If I personally wanted to do software compression on the fly, I
> would probably either use gzip (-5) or gzip -1 piping through dd
> with blocksize specifications and also use the hardware compression

AWHOOOGAH!  AWHOOOGA!

*Bad* idea.  Using software (-5 is only one step down from the gzip
default) and hardware compression at the same time will only make the
backup images faster.

jason
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