On Thu, Apr 24, 2003 at 11:45:02AM -0400, Mitch Collinsworth wrote:
> On Thu, 24 Apr 2003, Jon LaBadie wrote:
> > On Thu, Apr 24, 2003 at 09:26:12AM -0500, Russell Adams wrote:
> > >
> > > I have to take issue with this. My experience with hardware
> > > compression on DDS and DLT drives is that when enabled it makes things
> > > incredibly slow.
> > >
> > > My DLT IV (er, 7000?) drives can do 4.9 MB/s uncompressed, and only
> > > 800KB/s in compressed mode.
> >
> > This is of course counter to advertising claims :))
> >
> > Are you sure there was not some other factor involved.  A possibility
> > that comes to mind is that the no-hw-compression came from data already
> > in a single file or local to the server while the with-hw-compression
> > test data had to be "found" and that procedure caused the slow down?
> 
> Yes, I agree.  This sounds suspicious.  The slowdown described sounds
> like exactly what happens with DLT4000 and DLT7000 when you can't feed
> them data fast enough to keep them streaming.  Supposedly this was fixed
> somewhat in DLT8000 but I never bought one to verify that claim.  I've
> never heard of anyone claiming this also happens with compression.


I mentioned earlier today attending a tape technology talk.
This sounds like the "adaptive speed" the presenter mentioned saying
that if the source could not keep up with the drive, rather than dropping
out of streaming mode it would switch to writing at a slower rate.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
 4455 Province Line Road        (609) 252-0159
 Princeton, NJ  08540-4322      (609) 683-7220 (fax)