* Jean-Francois Malouin <Jean-Francois.Malouin AT bic.mni.mcgill DOT ca> 
[20070801 14:05]:
> * Joshua Baker-LePain <jlb17 AT duke DOT edu> [20070801 12:20]:
> > On Wed, 1 Aug 2007 at 11:29am, Jean-Francois Malouin wrote
> 
> Hi Joshua,
> 
> > 
> > >Hardware:
> > >I've setup the default access device to the drives as non-compressing.
> > >The library is hooked through a LSI U320 PCI-X scsi card to a 4
> > >DualCore2 Xeon with 8GB of RAM running Debian/Etch running a 64bit
> > >kernel 2.6.21.5-i686-64-smp. It should be beefy enough :)
> > 
> > If you ever want to use both drives simultaneously, you'll need a dual 
> > channel SCSI card and each drive will need to be on its own channel. 
> > Trust me on this one -- I tried every trick I could think of with 2 drives 
> > on one channel (there should be plenty of bandwidth, right!?), but 
> > couldn't get decent speeds when using both drives.
> 
> I tried running amtapetype simultaneously and on each tape on it's own
> and I didn't see any differences in the transfer rates but since they
> seem to throttle back to half-speed maybe I wasn't hitting their
> bottlenecks.

My bad, replying to myself...
Here's the outpout of 2 simultaneous running dd's on non-compressing
tape devices daisy-chained to the same scsi hba (LSI U320 PCI-X):

grumpy:~# time dd if=/dev/zero of=/dev/nst0 bs=32k
dd: writing `/dev/nst0': No space left on device
12424636+0 records in
12424635+0 records out
407130439680 bytes (407 GB) copied, 7003.39 seconds, 58.1 MB/s

real    116m43.419s
user    0m11.317s
sys     3m7.260s

grumpy:~# time dd if=/dev/zero of=/dev/nst1 bs=32k
dd: writing `/dev/nst1': No space left on device
12424636+0 records in
12424635+0 records out
407130439680 bytes (407 GB) copied, 7002.45 seconds, 58.1 MB/s

real    116m42.477s
user    0m11.677s
sys     3m6.480s

Looks good to me.
Not sure why amtapetype tops at 40MBs. 

jf
-- 
<° ><