The high interrupt load vanished after removing the CD-ROM drives from both V210, as suggested by Mark Kettenis.
Now the CPU load is down to 0%, as one expects, and the systems are much more performant and responsive than before :-) # iostat -w 1 tty cd0 sd0 cpu tin tout KB/t t/s MB/s KB/t t/s MB/s us ni sy in id 0 21 0.00 0 0.00 8.18 2 0.01 3 0 0 36 61 0 172 0.00 0 0.00 0.00 0 0.00 0 0 0 0100 0 57 0.00 0 0.00 0.00 0 0.00 0 0 0 0100 0 57 0.00 0 0.00 0.00 0 0.00 0 0 0 0100 0 57 0.00 0 0.00 0.00 0 0.00 0 0 0 0100 0 57 0.00 0 0.00 0.00 0 0.00 0 0 0 0100 0 57 0.00 0 0.00 16.00 2 0.03 0 0 0 0100 0 57 0.00 0 0.00 0.00 0 0.00 0 0 0 0100 ^C # Thanks to Mark for his suggestion, Rolf