If I look at the other disks log from the same server, it does not
really take time to do the backup, but for my particular problem disk
(/disk1) here's what I have in the sendbackp.debug log:

---------------------

sendbackup: debug 1 pid 12853 ruid 555 euid 555: start at Tue Aug
 30 04:39:46 2005
/usr/local/libexec/sendbackup: version 2.4.5
  parsed request as: program `GNUTAR'
                     disk `/disk1'
                     device `/disk1'
                     level 1
                     since 2005:8:27:9:4:40
                     options `|;bsd-auth;srvcomp-best;index;exclu
de-list=.amanda.excludes;exclude-optional;'
sendbackup: try_socksize: send buffer size is 65536
sendbackup: time 0.000: stream_server: waiting for connection: 0.
0.0.0.50025
sendbackup: time 0.000: stream_server: waiting for connection: 0.
0.0.0.50026
sendbackup: time 0.001: stream_server: waiting for connection: 0.
0.0.0.50027
sendbackup: time 0.001: waiting for connect on 50025, then 50026,
 then 50027
sendbackup: time 0.003: stream_accept: connection from 192.197.12
4.40.50054
sendbackup: time 0.004: stream_accept: connection from 192.197.12
4.40.50056
sendbackup: time 0.006: stream_accept: connection from 192.197.12
4.40.50057
sendbackup: time 0.006: got all connections
sendbackup-gnutar: time 0.050: doing level 1 dump as listed-incre
mental from /usr/local/var/amanda/gnutar-lists/sol_disk1_0 to /us
r/local/var/amanda/gnutar-lists/sol_disk1_1.new
sendbackup-gnutar: time 0.067: doing level 1 dump from date: 2005
-08-27  9:04:40 GMT
sendbackup: time 0.069: spawning /usr/local/libexec/runtar in pip
eline
sendbackup: argument list: gtar --create --file - --directory /di
sk1 --one-file-system --listed-incremental /usr/local/var/amanda/
gnutar-lists/sol_disk1_1.new --sparse --ignore-failed-read --tota
ls --exclude-from /tmp/amanda/sendbackup._disk1.20050830043946.ex
clude .
sendbackup: time 0.074: started index creator: "/usr/local/bin/ta
r -tf - 2>/dev/null | sed -e 's/^\.//'"
sendbackup-gnutar: time 0.081: /usr/local/libexec/runtar: pid 128
56
sendbackup: time 6032.881: index created successfully
sendbackup: time 6032.923:  53:    size(|): Total bytes written:
5467463680 (5.1GiB, 886KiB/s)
sendbackup: time 6032.969: pid 12853 finish time Tue Aug 30 06:20
:19 2005

---------------

It started at 4h39 and finished at 6h20 ! It really took a LONG time.
Why, I don't know.