Does Power-Management Affect a Hard-Drive’s SMART Statistics?
Among the various fields in a hard-drive’s SMART statistics, a few are flagged as “life-critical”, that is, those values determine the primary health of the drive and how long it may have left before catastrophic failure. Regardless, each field contributes to the overall health of the drive.
I have always wondered about how power-management affects SMART data (and before the electric company recently jacked prices, I was resistant to use power-management for fear of adding wear to the drives, specifically because the SMART data keeps logs like this, thus allowing me to visibly see the wear accumulating). Basically, does power-management affect a hard-drive in the same way as turning the whole system on or off?
There are at least two fields in particular that would ostensibly be directly affected by power-management:
- Start/Stop Count
Drive Power Cycle Count
Load Cycle Count (which usually equals Drive Power Cycle Count)
while some other fields would probably be indirectly affected:
- Spin Up Time
- Spin Retry Count
- Power Off Retract Count
- Calibration Retry Count
and some fields would be directly affected, but positively:
- Power On Hours Count
- Temperature
Anyway, I’ve tried testing it, but have not been able to determine or confirm if power-management functions affect the SMART data. That is, if an idling system shuts down a hard-drive that is not being used, or the whole system goes into standby mode, would the hard-drive log it in the SMART table (eg incrementing the Start/Stop and Power Cycle counts)? In other words, from the drive’s point of view, is power-management the same as normal shutdown/startup?
Solution 1:
Looking at the list of SMART values at Wikipedia, I couldn't find any values that would be affected by Power Management and that you didn't listed.
However, I would like to add that only Spin Retry Count as marked as "Vital", which means all other values are informative only.
What is notable is that the values of Start/Stop Count and Power Cycle Count will be different with Power Management enabled (as you suspected):
The difference between Start/Stop Count and Power Cycle Count is based on embedded controller and spindle. Single power-on increases both values by 1 (hard disk controller and spindle have been started), but after this operation Power Cycle Count will not change until hard disk power-off and next power-on.
However, while being in power-on state hard disk can go into sleep mode, which slows down a spindle. After returning from sleep mode to normal work, spindle is running again and Start/Stop Count attribute increases by 1 (second time). This situation is specially noticable while using ACPI/APM (Advanced Configuration and Power Interface / Advanced Power Management).
At the other hand, when you turn-off computer, hard disk controller automatically changes it's state to 0, but it takes a little bit of time for spindle to slow down. If you power-on hard disk quickly (before spindle goes completely down) Power Cycle Count will increase, but Start/Stop Count don't (as spindle is still working and it doesn't had a full cycle). One full cycle means a single change of state from 0 to 1 (off -> on).
Source: http://smartlinux.sourceforge.net/smart/article.php (linked also from the Wikipedia article).