That's what can be found on the web:   Overstrained Read/Write heads of WD's Green Power 

The Read/Write heads are run on energy saving mode if there hasn't been an activity for about eight seconds. Several Linux distributions access the hard drive in regular patterns - sometimes in a 10 seconds rhythm - and thus unnecessarily use the hard drive. The affected hard drives can be recognized by a high load/unload cycle; via SMART. Some Green Power hard drives are supposed to have exceeded their specified 300,000 cycles in less than a year.  There is a new firmware for Western Digital's Green Power hard drives that is supposed to solve problems related to the combination of energy saving mode and certain programs. 

Here are the important smart attributes for the drives installed in fb1. The tool i used is "smartmontools" written by Bruce Allen. The first two disks don't have this parameter as they are old(er).


SDA:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  4  Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       45
  9  Power_On_Hours          0x0032   052   051   000    Old_age   Always       -       35686
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       45

SDB:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       39
  9 Power_On_Hours          0x0032   045   045   000    Old_age   Always       -       40385
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       39

SDC:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       19
  9 Power_On_Hours          0x0032   087   087   000    Old_age   Always       -       9587
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       17
193 Load_Cycle_Count        0x0032   200   200   000    Old_age   Always       -       19

SDD:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       13
  9 Power_On_Hours          0x0032   087   087   000    Old_age   Always       -       9521
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       12
193 Load_Cycle_Count        0x0032   200   200   000    Old_age   Always       -       13

So for fb1 everything is fine but i didn't check fb0 as i'm not allowed to install anything there.