You can see that Amanda correctly estimates the size at estimated 4752738
tape blocks
But actually dumps  DUMP: 9029315 tape blocks

sendbackup: debug 1 pid 11410 ruid 2 euid 2: start at Wed Jun 25 00:11:00
2003
/usr/local/libexec/amanda/sendbackup: version 2.4.3
  parsed request as: program `DUMP'
                     disk `ad0s1f'
                     device `ad0s1f'
                     level 0
                     since 1970:1:1:0:0:0
                     options `|;auth=bsd;'
sendbackup: try_socksize: send buffer size is 65536
sendbackup: time 0.000: stream_server: waiting for connection: 0.0.0.0.3690
sendbackup: time 0.000: stream_server: waiting for connection: 0.0.0.0.3691
sendbackup: time 0.002: waiting for connect on 3690, then 3691
sendbackup: time 0.002: stream_accept: connection from 555.555.555.555.3692
sendbackup: time 0.002: stream_accept: connection from 555.555.555.555.3693
sendbackup: time 0.002: got all connections
sendbackup: time 0.004: dumping device '/dev/ad0s1f' with 'ufs'
sendbackup: time 0.004: spawning /sbin/dump in pipeline
sendbackup: argument list: dump 0ushf 1048576 0 - /dev/ad0s1f
sendbackup: time 0.007:  91:  normal(|):   DUMP: Date of this level 0 dump:
Wed Jun 25 00:11:00 2003
sendbackup: time 0.008:  91:  normal(|):   DUMP: Date of last level 0 dump:
the epoch
sendbackup: time 0.008:  91:  normal(|):   DUMP: Dumping /dev/ad0s1f (/usr)
to standard output
sendbackup: time 0.073:  91:  normal(|):   DUMP: mapping (Pass I) [regular
files]
sendbackup: time 17.649:  91:  normal(|):   DUMP: mapping (Pass II)
[directories]
sendbackup: time 17.650:  91:  normal(|):   DUMP: estimated 4752738 tape
blocks.
sendbackup: time 17.685:  91:  normal(|):   DUMP: dumping (Pass III)
[directories]
sendbackup: time 59.543:  91:  normal(|):   DUMP: dumping (Pass IV) [regular
files]
sendbackup: time 317.292:  91:  normal(|):   DUMP: 20.79% done, finished in
0:19
sendbackup: time 617.280:  91:  normal(|):   DUMP: 46.31% done, finished in
0:11
sendbackup: time 917.279:  91:  normal(|):   DUMP: 65.08% done, finished in
0:08
sendbackup: time 1217.355:  91:  normal(|):   DUMP: 84.36% done, finished in
0:03
sendbackup: time 1517.287:  91:  normal(|):   DUMP: 104.80% done, finished
in 0:-1
sendbackup: time 1817.284:  91:  normal(|):   DUMP: 121.45% done, finished
in 0:-5
sendbackup: time 2117.284:  91:  normal(|):   DUMP: 138.32% done, finished
in 0:-9
sendbackup: time 2417.280:  91:  normal(|):   DUMP: 161.07% done, finished
in 0:-15
sendbackup: time 2684.483:  49:    size(|):   DUMP: DUMP: 9029315 tape
blocks
sendbackup: time 2684.518:  91:  normal(|):   DUMP: finished in 2667
seconds, throughput 3385 KBytes/sec
sendbackup: time 2684.526:  91:  normal(|):   DUMP: level 0 dump on Wed Jun
25 00:11:00 2003
sendbackup: time 2684.529:  91:  normal(|):   DUMP: DUMP IS DONE
sendbackup: time 2684.530: pid 11410 finish time Wed Jun 25 00:55:45 2003