Dan,

A DLT7000 has a throughput of 5MB/sec with compression turned off and
10MB/sec with compression on and data that is being compressed by the
DLT7000 in a ratio of 2 to 1. If you have ADSM compression enabled, the
DLT7000 will probably not be able to get any worthwhile compression done
trying to compress data that has already been compressed by ADSM client
software.

Thus, I would not expect any significant performance improvement going
from 2 drives per SCSI channel to one drive per SCSI channel. The SCSI
channel utilisation would drop from 50% to 25% with only a small
performance improvement.

If on the other hand, you were not using ADSM compression and the
DLT7000 was compressing by 2 to 1, the SCSI channel utilisation would
drop from about 100% to about 50% and the improvement would be a bit
higher.

If you had 3 DLT7000s on a single fast/wide 20MB/sec SCSI without ADSM
compression, there would definitely be a SCSI channel bottleneck and you
would see a significant performance improvement going from 3 drives per
SCSI to either 2 or 1 drive per SCSI.

Best regards .... John Rajca (Australian Gas Light Company)

 
=====================================================================================================
Dan Giles wrote:
>
> We have 3 DLT7000 drives in a Stk 9710 library connected to our adsm server
> (currently 2.1.12) running on an F30.
>
> The way we had it configured was that the 9710 and one DLT was on one SCSI
> adaptor, and the other 2 DLT's were on a second adaptor. We recently got a 
> third
> adaptor so that each DLT now has its own SCSI adaptor. I thought I would see a
> big performance boost when it comes to tape-to-tape activity, but so far it
> doesn't appear that this is the case.
>
> Is there anyone out there running multiple high-speed tape drives on a single
> SCSI adaptor? Do you have any performance issues regarding this configuration?
> Being on an F30, I'm out of PCI slots and really need to get a fourth drive 
> on.
> I would like to know from other's experience whether I should try to free a 
> slot
> up somehow for another adapter, or just go ahead and double-up again.
>
> Thanks in advance.