# hdparm -J 12 /dev/sda
/dev/sda:
Use of -J is EXTREMELY DANGEROUS.
This implementation is not as thorough as the official WDIDLE3.EXE. Use at your own risk!
Please also supply the --please-destroy-my-drive flag if you really want this.
Program aborted.
#

J             Get/set the Western Digital (WD) Green Drive's  "idle3"  timeout
              value.   This  timeout  controls  how  often the drive parks its
              heads and enters a low power  consumption  state.   The  factory
              default  is  eight  (8) seconds, which is a very poor choice for
              use with Linux.  Leaving it at the default will result  in  hun‐
              dreds  of  thousands  of head load/unload cycles in a very short
              period of time.  The drive mechanism is only rated  for  300,000
              to  1,000,000  cycles, so leaving it at the default could result
              in premature failure, not to mention the performance  impact  of
              the drive often having to wake-up before doing routine I/O.

              WD  supply  a WDIDLE3.EXE DOS utility for tweaking this setting,
              and you should use that program instead of hdparm if at all pos‐
              sible.   The  reverse-engineered implementation in hdparm is not
              as complete as the original official  program,  even  though  it
              does  seem  to  work  on  at a least a few drives.  A full power
              cycle is required for any change  in  setting  to  take  effect,
              regardless of which program is used to tweak things.

              A setting of 30 seconds is recommended for Linux use.  Permitted
              values are from 8 to 12 seconds, and from 30 to 300  seconds  in
              30-second  increments.   Specify  a value of zero (0) to disable
              the WD idle3 timer completely (NOT RECOMMENDED!).