I've read the amstatus docs and the "using amanda" chapter. Somehow, I
can't quite figure how to interpret the amstatus output.

This morning I did:

amstatus DailySet1 and got:

--------------SNIP------------------

SUMMARY          part      real  estimated
                           size       size
partition       :  46
estimated       :  46                 8326m
flush           :   0         0m
failed          :   1                  789m           (  9.49%)
wait for dumping:   0                    0m           (  0.00%)
dumping to tape :   0                    0m           (  0.00%)
dumping         :   0         0m         0m (  0.00%) (  0.00%)
dumped          :  45      7748m      7536m (102.82%) ( 93.07%)
wait for writing:   0         0m         0m (  0.00%) (  0.00%)
wait to flush   :   0         0m         0m (100.00%) (  0.00%)
writing to tape :   0         0m         0m (  0.00%) (  0.00%)
failed to tape  :   0         0m         0m (  0.00%) (  0.00%)
taped           :  45      7748m      7535m (102.83%) ( 93.07%)
  tape 1        :  45      7748m      7535m ( 51.66%) DailySet1-023
10 dumpers idle : not-idle
taper idle
network free kps:     68000
holding space   :    177609m (100.00%)
 dumper0 busy   :  2:07:26  ( 53.16%)
 dumper1 busy   :  3:20:27  ( 83.61%)
 dumper2 busy   :  0:51:03  ( 21.30%)
 dumper3 busy   :  1:42:58  ( 42.95%)
 dumper4 busy   :  0:01:17  (  0.54%)
 dumper5 busy   :  2:25:43  ( 60.78%)
 dumper6 busy   :  0:53:10  ( 22.18%)
 dumper7 busy   :  0:00:30  (  0.21%)
 dumper8 busy   :  0:00:07  (  0.05%)
 dumper9 busy   :  0:00:07  (  0.05%)
   taper busy   :  1:41:14  ( 42.23%)
 0 dumpers busy :  0:37:11  ( 15.51%)             no-hold:  0:31:17  ( 84.14%)
                                                 not-idle:  0:05:53  ( 15.86%)
 1 dumper busy  :  0:55:09  ( 23.01%)             no-hold:  0:54:48  ( 99.35%)
                                       client-constrained:  0:00:13  (  0.39%)
                                                 not-idle:  0:00:08  (  0.26%)
 2 dumpers busy :  0:19:53  (  8.30%)             no-hold:  0:19:43  ( 99.18%)
                                               start-wait:  0:00:07  (  0.62%)
                                       client-constrained:  0:00:02  (  0.20%)
 3 dumpers busy :  0:24:53  ( 10.39%)             no-hold:  0:24:53  ( 99.95%)
 4 dumpers busy :  0:49:21  ( 20.59%)             no-hold:  0:49:05  ( 99.46%)
                                       client-constrained:  0:00:11  (  0.40%)
                                               start-wait:  0:00:04  (  0.14%)
 5 dumpers busy :  0:02:25  (  1.01%)             no-hold:  0:02:19  ( 96.05%)
                                       client-constrained:  0:00:05  (  3.85%)
 6 dumpers busy :  0:50:24  ( 21.03%)             no-hold:  0:47:42  ( 94.64%)
                                       client-constrained:  0:02:41  (  5.33%)
 7 dumpers busy :  0:00:10  (  0.08%)  client-constrained:  0:00:10  ( 95.27%)
 8 dumpers busy :  0:00:01  (  0.01%)          start-wait:  0:00:01  (100.00%)
 9 dumpers busy :  0:00:00  (  0.00%)
10 dumpers busy :  0:00:00  (  0.00%)

-----------/SNIP-----------------

My holding disk has about 180Gb free. The amanda.conf definition is:

holdingdisk hd1 {
    comment "main holding disk"
    directory "/disk1/amanda/hd"        # where the holding disk is
    use -500 Mb         # how much space can we use on it
                        # a non-positive value means:
                        #        use all space but that value
    chunksize 1990 Mb   # size of chunk if you want big dump to be
                        # dumped on multiple files on holding disks
                        #  N Kb/Mb/Gb split images in chunks of size N
                        #             The maximum value should be
                        #             (MAX_FILE_SIZE - 1Mb)
                        #  0          same as INT_MAX bytes
    }

reserve 30

If I understand well:

There remains approx 179.5 gb (180 Gb - 500 mb) in the holding disk.
Minis 30% reserved for degraded mode backups. I should Have something
like 200 Gb - 500 Mb - 30% = 125 Gb holding space.

Last amdump run dumped about 7.7 Gb total to tape.

Why does amanda asy that there is no holding space available for
almost 100% of the time ?