I have a Maxtor Corporation Personal Storage 3100 external USB disk.
This device works fine when connected to USB 1.0 port(s), but times out
at random when connected to USB 2.0 port(s).

OE is Solaris10 03/05 x86.

I get the following messages on the console:

Dec 11 11:45:48 minas-ithil scsi: WARNING:
/pci@0,0/pci2020,8888@a,3/storage@6/disk@0,0 (sd46):
Dec 11 11:45:48 minas-ithil SCSI transport failed: reason 'timeout':
giving up
Dec 11 11:47:12 minas-ithil scsi: WARNING:
/pci@0,0/pci2020,8888@a,3/storage@6/disk@0,0 (sd46):
Dec 11 11:47:12 minas-ithil SCSI transport failed: reason 'timeout':
giving up
Dec 11 11:48:36 minas-ithil scsi: WARNING:
/pci@0,0/pci2020,8888@a,3/storage@6/disk@0,0 (sd46):
Dec 11 11:48:36 minas-ithil SCSI transport failed: reason 'timeout':
giving up
Dec 11 11:50:08 minas-ithil scsi: WARNING:
/pci@0,0/pci2020,8888@a,3/storage@6/disk@0,0 (sd46):
Dec 11 11:50:08 minas-ithil SCSI transport failed: reason 'timeout':
giving up
Dec 11 11:51:32 minas-ithil scsi: WARNING:
/pci@0,0/pci2020,8888@a,3/storage@6/disk@0,0 (sd46):
Dec 11 11:51:32 minas-ithil SCSI transport failed: reason 'timeout':
giving up

....and so on, ad nauseam. This happens when a process or several
processes are writing, or trying to write to the device while reading
from it at the same time.

For example:

cd /rmdisk/rmdisk0/
unzip -x sol-nv-b27a-sparc-v2-iso.zip

Finally, here is the relevant part of my /kernel/drv/scsa2usb.conf:

attribute-override-list =
"vid=* modesense=false reduced-cmd-support=true pmoff=true";

Note that the "pmoff=true" does not seem to be changed, at least it's
not being reported as overriden in /var/adm/messages.

What is actually the problem here, and why is the SCSI transport timing
out??? What does that even mean in this case???
What do I need to do to fix this???