Amdump issues
If you have any problem with amdump first make sure that the command amcheck still succeeds. The amcheck command also points you to a much more detailed and to the point problem area than e.g. the amdump error "all disks failed"
Here is list of issues that amdump may encounter:
Amdump: dumps way too big, must skip incremental dumps
Amdump: infofile update failed
Amdump: cannot overwrite active tape
Why does 'amdump' not dump to the holding disk?
Why does 'amdump' give me 'Tape I/O error'?
Why does 'amdump fail to create level 0 dump'
Amdump fails to backup large DLEs
Issues with other Amanda programs: see Troubleshooting