Craig White schrieb:
> On Wed, 2009-01-07 at 17:57 +0100, Ralf Gross wrote:
> > T. Horsnell schrieb:
> > > Ralf Gross wrote:
> > > > Ferdinando Pasqualetti schrieb:
> > > >> I think you should use /dev/random, not /dev/zero unless hardware 
> > > >> compression is disabled in order to have more realistic figures.
> > > > 
> > > > This wouldn't be a good idea, /dev/random or /dev/urandom are just too
> > > > slow in generating random data. To test the nativ speed of the  drive
> > > > creating a file from /dev/urandom and writing this file then from
> > > > tmpfs or a fast disk to the drive would be much better.
> > > > 
> > > > 
> > > > Ralf
> > > 
> > > Personally, I'd use /dev/zero with compression turned off.
> > > Then there's *nothing* between the data-source and the tapedrive.
> > 
> > Yes, but most people use hardware compresion with LTO drives. Sooner
> > or later he has to test the drive with compression.
> ----
> funny thing is that amanda developers are adamant that you disable
> hardware compression and use software compression instead.

With Bacula and LTO-4 drives I get 80 MB/s and a compression rate of
1,4:1. It would be fun to backup several TB with gzip compression.

 
> Obviously it takes longer and more cpu power to compress the files in
> software before storing them on the tape and if you leave hardware
> compression on and use software compression too, the files probably grow
> in size.

Not with LTO drives.

http://en.wikipedia.org/wiki/Linear_Tape-Open#LTO-DC
 
> Commercial backup software just seems to always use hardware
> compression.

Which is not the worst idea.


Ralf

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