Yet Another NAS – HP Microserver N40L – Hard drive Loading/Unloading Cycles

I have a combination of Seagate Barracuda Green (ST2000DL003-9VT166) drives and Western Digital Red (WDC WD30EFRX-68AX9N0) drives. The latter is designed for NAS application and the former is designed in an era where NAS optimized hard drives are not commonplace yet. The 2 x 3TB WD Red drives were previously purchased just for the HP N40L NAS. The other 3 x Seagate Barracuda drives were transplanted from my Buffalo Linkstation Quad Pro. My Quad Pro has 1 more Seagate Barracuda Green drive and 2 more WD Greens which I salvaged from the external hard drives. The WD Greens have aggressive head parking issues and these have been fixed via the firmware patch.

So I happen to have some spare time up my sleeve today and I carry out a quick status check using the UnRaid interface. It is easy to run this command using the Smartctl at the command line as well but I am lazy.

The SMART attributes of the hard drive will look something like this. Here is the screenshot of my parity drive which is a Western Digital Red.

2014-04-05 16_01_47-Defiant unRAID Server

I am mainly interested in the following 3 parameters: Power_On_hours, Power_Cycle_Count and Load_Cycle_Count. So I checked all my drives the same way and the results are tabulated here.

 SMART Attributes  Western Digital Red (Parity)  Western Digital Red 1  Seagate Barracuda Green 1  Seagate Barracuda Green 2  Seagate Barracuda Green 3
Power_On_Hours 9136 9136 60065 56519 33036
Power_Cycle_Count 16 16 95 96 108
Load_Cycle_Count 890 1008 841 1177 173

Created with the HTML Table Generator

What exactly are those parameters Power_Cycle_Count and Load_Cycle_Count?

The SMART Attributes of a hard drive are extremely cryptic and most users (including myself) have no idea what the parameters are referring to and how significant (or not) these figures represent. Fortunately there are smarter people out there…. A quick google reveals the following useful resources. There are obviously a lot more info out there.

According to Wikipedia,

  • Power Cycle Count refers to the count of full hard disk power on/off cycles and
  • Load Cycle Count refers to the count of load/unload cycles into head landing zone position.

According to this document (, Western Digital Red is rated to have a 600,000 load/unload cycles. I don’t know what is Western Digital Red’s rated power cycle count as it is not stated anywhere.

So for my Western Digital Red that I have, the load cycle count for one of the drive is 1008 (to date) and it has a power on hours of 9,136 hours. A simple arithmetic tells me that this translates to a head parking event happening at every 9 hours or so.

The Seagate Barracuda Green drives are a lot more impressive. For Seagate drive 1, over the course of 60,065 hours, the drive parks only for 841 times. This is 1 head parking cycle per 71.4 hours. The other 2 Barraccuda Green drives average about 1 cycle per 47.7 hours and 190.9 hours respectively.

So we are talking about drives that has a head parking event every 9 hours vs one that takes place every 50 hours. That’s a big difference. Having said this, the Western Digital Red is rated for 600,000 cycles so this is not alarming to me at this stage but it is good for me to know this. A quick google reveals that some of the Western Digital Red are shipped with an aggressive head parking like the notorious Western Digital Greens. Apparently Western Digital has published a firmware fix here ->

For my next hard drive purchase, I might have to look harder into whether I should be buying another Western Digital Red or go with the Seagate NAS drive. There are other options such as the Hitachi HGST drives but they appear to be more expensive.

Till next time, happy nas’ing :-)