After buying a new Mac Mini, I quickly became aware of a rather annoying clicking sound. Imagine sitting in a quiet room, working silently, then hearing a soft clicking sound. Imagine this sound happening seemingly randomly, at a frequency of about once every 5 minutes. It drove me up the wall.

I did a lot of searching, combing of various forums, and came up with some threads with similar problems. This problem isn’t very well documented or discussed, and I despair to think of the number of hard drives suffering from early demise due to this.

Retail hard drives have their own power management and motion sensors, and Apple doesn’t expect them to. They ship their own drives with these features dialed back, and handle the controls at the OS level. So we have a situation where both the OS and the hard drive are attempting to control the drive’s activity, in particular when it parks its drive heads, and it serves to drive up the load cycles.

Diagnostics

I was curious if this problem happened only in my circumstances, so I borrowed 2 laptops from my parents and ran some diagnostics. I was just a bit shocked with the results:

Thinkpad x60s, Toshiba MK6032GSX (stock, 3 years old)
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   3607
  9 Power_On_Hours          0x0032   094   094   000    Old_age   2513
192 Power-Off_Retract_Count 0x0032   100   100   000    Old_age   51
193 Load_Cycle_Count        0x0032   088   088   000    Old_age   126449

Thinkpad x61t, Hitachi Travelstar 7K100 (stock, 2 years old)
  4 Start_Stop_Count        0x0012   099   099   000    Old_age   2467
  9 Power_On_Hours          0x0012   079   079   000    Old_age   9625
192 Power-Off_Retract_Count 0x0032   100   100   000    Old_age   1175060616
193 Load_Cycle_Count        0x0012   088   088   000    Old_age   129851

Western Digital Scorpio Black 320 (retail, brand new, installed 29 hours ago)
  9 Power_On_Hours          0x0032   100   100   000    Old_age   29
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   12
193 Load_Cycle_Count        0x0032   200   200   000    Old_age   1908

Western Digital Raptor 150 (retail, year old application drive)
 4  Start_Stop_Count        0x0032   100   100   000    Old_age   197
 9  Power_On_Hours          0x0032   084   084   000    Old_age   12126
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   188

Toshiba
 - Cycles per hour: ~50

Hitachi
 - 1,174,460,616 cycles over lifetime
 - Cycles per hour: ~13
 - Emergency head parks per hour: 122,084

WD Scorpio
 - Cycles per hour: ~65

The Toshiba drive seems just fine. Its seen light use, and the hard drive shows it. The Hitachi drive however, concerned me. Its seen 3 times the power on hours of the Toshiba, yet seen 23 million times the number of emergency head parks.

The Mac Mini’s brand new WD Scorpio Black had a very high load cycle count for a drive 29 hours old. If the drive continues to get 1908 cycles per day, at the end of a year it will be at 696,420. Most hard drive have a guaranteed load/unload cycle duty of 600,000. This puts the drive well beyond the advertised number of cycles.

Dealing With It

The novice user should never encounter this problem. They’ll use Apple’s stock hard drives, get replacements and upgrades directly from Apple, and all will be well. If you’re the type of person who upgrades their own internal drive, or buys an external enclosure and a drive for storage, you’re going to have to deal with this.

The solutions I ended up adopting were twofold: For my external drives, I buy Western Digital; they provide tools to alter the drive’s power management settings. For my internal drives, I run hdapm to achieve the same result.