Well, so much for the NIC and switch causing the amanda slowdown. I
changed the settings on my NIC last night before the amanda run to
100baseT-FD. However, the dump is still running now, 15 hours later. I'm
going to examining the switch shortly to see if there were many errors
or collisions.

Here's what amstatus said a few minutes ago:
amanda@admin:~ > amstatus DailySet1
Using /var/log/amanda/DailySet1/amdump from Thu Aug  8 18:00:00 EDT
2002

admin://db/c$                            1     380k finished
(18:14:30)
admin://db/e$                            1      10k finished
(18:13:21)
admin://db/f$                            0 7066846k wait for dumping 
admin:sda1                               1      10k finished
(18:13:37)
admin:sda3                               1    3085k wait for dumping 
admin:sdb1                               0    3970k finished
(18:13:54)
centernet:sda1                           0    2975k finished
(18:16:12)
centernet:sda3                           0 1564325k finished (8:22:23)
centernet:sdb1                           1    1581k finished
(18:14:42)
centernet:sdb2                           0   70452k finished
(18:52:25)
centernet:sdc1                           1       1k finished
(18:13:22)
cgi:hda1                                 0    2294k finished
(18:13:56)
cgi:hda3                                 0  604189k finished (8:39:55)
kzlaptop:hda5                            0    4181k finished
(18:16:44)
kzlaptop:hda7                            1    1926k finished
(18:16:16)
mailinglists:hda1                        0     943k finished
(18:15:37)
mailinglists:hda2                        1    7725k finished
(18:18:42)
mailinglists:hda7                        1      41k finished
(18:15:24)
virtual:hda1                             0     944k finished
(18:13:35)
virtual:hda3                             0 1432404k writing to tape
(8:57:43)
www2:sda10                               0 [Request to www2 timed
out.]
www2:sda11                               0 [Request to www2 timed
out.]
www2:sda5                                0 [Request to www2 timed
out.]
www2:sda7                                0 [Request to www2 timed
out.]
www2:sda8                                0 [Request to www2 timed
out.]
www2:sda9                                0 [Request to www2 timed
out.]

SUMMARY          part     real estimated
                          size      size
partition       :  26
estimated       :   0                  0k
failed          :   6                  0k           (  0.00%)
wait for dumping:   2            7069931k           (  0.00%)
dumping to tape :   0                  0k           (  0.00%)
dumping         :   0        0k        0k (  0.00%) (  0.00%)
dumped          :  18  3698351k  4633924k ( 79.81%) (  0.00%)
wait for writing:   0        0k        0k (  0.00%) (  0.00%)
writing to tape :   1  1432404k  1342192k (106.72%) (  0.00%)
failed to tape  :   0        0k        0k (  0.00%) (  0.00%)
taped           :  17  2265947k  3291732k ( 68.84%) (  0.00%)
8 dumpers idle  : no-diskspace
taper writing, tapeq: 0
network free kps:     2600
holding space   :  2062091k ( 59.01%)
 dumper0 busy   : 14:14:54  ( 96.67%)
 dumper1 busy   : 13:38:37  ( 92.57%)
 dumper2 busy   :  0:05:06  (  0.58%)
 dumper3 busy   : 14:44:22  (100.00%)
 dumper4 busy   :  0:03:14  (  0.37%)
 dumper5 busy   :  0:00:59  (  0.11%)
   taper busy   :  0:42:07  (  4.76%)
 0 dumpers busy :  0:00:00  (  0.00%)
 1 dumper busy  :  0:28:59  (  3.28%)        no-bandwidth:  0:28:59 
(100.00%)
 2 dumpers busy :  0:36:32  (  4.13%)        no-bandwidth:  0:36:32 
(100.00%)
 3 dumpers busy : 13:33:43  ( 92.01%)        no-bandwidth: 13:33:42 
(100.00%)
 4 dumpers busy :  0:02:06  (  0.24%)        no-bandwidth:  0:01:54  (
90.50%)
                                               start-wait:  0:00:12  ( 
9.50%)
 5 dumpers busy :  0:02:30  (  0.28%)        no-bandwidth:  0:02:03  (
82.11%)
                                       client-constrained:  0:00:25  (
17.09%)
                                               start-wait:  0:00:01  ( 
0.80%)
 6 dumpers busy :  0:00:30  (  0.06%)        no-diskspace:  0:00:15  (
49.47%)
                                             no-bandwidth:  0:00:12  (
40.64%)
                                       client-constrained:  0:00:02  ( 
6.82%)
amanda@admin:~ > 

In the first section, the admin://db/f$ is a samba connection to a
Windows NT host through the tapebackup host. The F: drive is primarily
one huge database file. The admin:sda3 is the root directory on the
tapebackup host itself. I should have commented out www2, since I know
it's a dead host.

What's the meaning of this line in the second section: "8 dumpers idle 
: no-diskspace" Is this an error message? Should I try to allocate more
disk space to the dump disk?

Do the last lines about 1-6 dumpers busy, due to no-bandwidth indicate
that I need to increase the netusage? I currently have "netusage  1200
Kbps     # maximum net bandwidth for Amanda, in KB per sec" Since I'm on
a 100baseT-FD line to the switch, can I increase this? Is my thinking
correct that I'm on a 100Mbps line, and have set the maximum bandwidth
usage to 1.2Mbps? If this is true, I would think I can surely increase
it. What's a prudent value, 25% of the line speed, 50%, 100%? The
backups run at night, where there's very little activity on our LAN.

Does the peak at 3 dumpers busy have any significance?

Thank you all again for your help and suggestions.

-Kevin