Intel 520 SSD SMART Power-on Hours Count behaviour

[APark9]

I have a 240GB Intel 520 SSD and have been puzzled by the behaviour of the SMART statistic 'Power-on Hours Count' (Attribute 09) displayed by the Intel SSD Toolbox utility. Others have also noted that this Power-on Hours Count statistic is strange and so this is not a fault that is specific to my SSD.

Intel have acknowleged that there is an issue with the SMART statistic 'Power-on Hours Count' -

See: http://www.intel.com/support/ssdc/hpssd/sb/CS-034131.htm http://www.intel.com/support/ssdc/hpssd/sb/CS-034131.htm

It would seem useful to know:

1. Do Intel plan to fix this Power-on Hours Count problem?
2. Do the Power-on Hours Count values shown have any useful meaning for a given Intel 520 SSD?
3. If so, then does this meaning also apply to other Intel 520 SSD units?

A response from Intel would be appreciated with regard to Question 1.

To address Question 2 I have done some investigation into the Power-on Hours Count behaviour for my 240GB Intel 520 SSD.

My PC was built with the Intel 520 SSD and two rotating disks. I have owned it for over a year and the Power-on Hours times for all three disks should be almost identical (the Power-on Hours Count values for the two rotating disks agree to within an hour).

Looking at snapshots of the Power-on Hours Count values taken at various times over the year it became evident that:

1. The Power-on Hours Count values for the two rotating disks were increasing at the same rate.
2. The Power-on Hours Count value for the Intel 520 SSD was also increasing, but at a somewhat slower rate.

Over a long period (around a year) the increase in the Power-on Hours Count for my Intel 520 SSD was 0.926 times the increase in the Power-on Hours Count values for the rotating disks. This seemed rather strange!

If the two rotating disks were correctly incrementing their counts every 60 mins then the Intel 520 SSD was incrementing every 64 min 48 sec - not a very obvious time period for an hour!

The other issue is that there appears to be a large base offset applied to the Intel 520 SSD Power-on Hours Count. Using the 0.926 ratio and extrapolating backwards it would appear that the base value when my SSD was first powered on was probably approximately 894,813.

So for my 240GB Intel 520 SSD the formula for converting the 'Power-on Hours Count' displayed by Intel SSD Toolbox (PoHC) into the actual Power-on Hours seems to be:

Actual Power-on Hours = (PoHC - 894,813) / 0.926

Does this formula (or a similar one) also work for Intel 520 SSDs owned by other users?

(See Question 3 above).

Some follow-on questions arose:

1. Do my rotating disks actually increment the Power-on Hours Count every 60 mins?
2. Does my Intel 520 SSD actually increment the Power-on Hours Count every 64 mins 48 sec?

This was rather difficult/tedious to investigate using Intel SSD Toolbox so I used a utility called System Information Viewer (SIV) from rh-software.com, which made the investigation much easier (I used Menu -> Tools -> Disk Status and left it running for a number of hours).

This showed that:

1. My rotating disks do increment the Power-on Hours Count every 60 mins.
2. The interval at which my Intel 520 SSD increments the Power-on Hours Count varies by several minutes. The shortest I have seen so far is 62 min 49 sec and the longest is 67 min 4 sec. (The mid-point between these values would be 64 min 57 sec, which is reasonably close to the long-term average of 64 min 48 sec mentioned above)

Do Intel 520 SSDs owned by other users also show this significant variation in the time taken to increment the Power-on Hours Count?

So in summary I have learnt that:

1. The interval at which my 240GB Intel 520 SSD increments the Power-on Hours Count varies by several minutes, with a long term average of about 64 min 48 sec.
2. My 240GB Intel 520 SSD Power-on Hours Count has a large base offset of approximately 894,813.

Do other Intel 520 SSD users see similar behaviour?

[Jose_H_Intel1]

Please allow us more time to check about your inquiry.

[APark9]

I now think that if the base offset is the same for all Intel 520 SSDs then the value is probably a few hours lower than my initial estimate above - possibly around 894,803.

[APark9]

I recently had access to the SMART statistics for another PC that has both a 240GB Intel 520 SSD and a rotating disk.

The Power-on Hours Count for this Intel 520 SSD increased by 544 in the same period that the Power-on Hours Count for the rotating disk increased by 551.

The Power-on Hours Count for the rotating disk seems to be incrementing correctly every 60 mins.

So the Power-on Hours Count for this Intel 520 SSD seems to be incrementing at a long-term average of

60*551/544 = 60 min 46 sec.

The time period between successive increments for the SSD varies - I observed successive periods of

61 min 33 sec, 61 min 3 sec and 61 min 43 sec (all measured to 10 sec granularity).

The estimated base offset for this Intel 520 SSD is around 894,811.

This is very close to the estimate of 894,813 given above for my Intel 520 SSD.

Both estimated figures could be out by a few hours depending on how the two PCs were initially built

(the SSDs and rotating disks could have been installed a few hours apart).

So it appears that the base offset may be the same (or very similar) for all Intel 520 SSDs, but the average period at which the Power-on Hours Count increments can vary between individual Intel 520 SSDs.

[APark9]

It would be useful to get some information from Intel about how to interpret the SMART statistic 'Power-on Hours Count' (Attribute 09) for a 520 Series SSD.

• Is there a definitive value for the base offset for all Intel 520 Series SSDs?
• What causes the variation in the period at which the Power-on Hours Count increments? (e.g. SSD read/write activity? Power Management?)
• Are there any upper or lower limits to the period at which the Power-on Hours Count increments? (e.g. Is the lower limit 60 minutes?)
• Is there likely to be a fix for this problem?