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' -
It would seem useful to know:
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:
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:
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:
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:
Do other Intel 520 SSD users see similar behaviour?
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.
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.
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.
I hope the following information answers your questions:
The description of Power-on hours count (09h) as explained in the specifications document:
"The raw value reports two values: the first 4 bytes report the cumulative number of power-on hours over the life of the device, the remaining bytes report the number of milliseconds since the last hour increment. The On/Off status of the Device Initiated Power Management (DIPM) feature will affect the number of hours reported.
If DIPM is turned On, the recorded value for power-on hours does not include the time that the device is in a "slumber" state. If DIPM is turned Off, the recorded value for power-on hours should match the clock time, as all three device states are counted: active, idle and slumber."
Therefore power management really affects this attribute. I know it is a different model but we have a similar discussion with more information here: /thread/48978 https://communities.intel.com/thread/48978
I had wondered about DIPM, however my Intel 520 SSD is installed in a desktop machine and I believed that DIPM was disabled.
According to the specification quoted above the recorded value for the power-on hours should therefore match the clock time.
I have just confirmed that DIPM is disabled using the Intel SSD Toolbox and the instructions given in the discussion thread that you referred to - Word 79 Bit 3 is set to zero.
So I am still puzzled...
Bit late in the day, but I have a system with two Intel 520 480GB SSDs in a RAID config, and two Western Digital 1TB hard disks in a separate RAID config.
The power-on hours counts are as follows:
The WDC hours average to 2.93 years
The SSD hours, using (base 894811 and 0.926 divisor), average to 1.17 years.
So I guess the base is not the same for all.
The SMART stats from the SSDs don't look all that plausible. I got this system in April 2013 and the SSDs still say normalised Media Wearout Indicator 100 (= no wear).
I wanted to know when to replace these SSDs before they fail on me. But it seems the stats are not much help.
As you may know the Power on Hours Count of the Intel® SSD 520 Series has an offset (894794) that has to be taken off the reported value to obtain the actual power on hours count.
The Media Wearout Indicator is actually the best way to determine the expected remaining life of your drive, as the normalized value declines from 100 to 1 as the average erase cycle count increases from 0 to the maximum rated cycles. Once it reaches 1, the SSD may continue to work well, however, it would mean that it reached the maximum rated cycles for the NAND memory.
Thanks. Yes, well as I clearly stated in my post, I have adjusted for the offset.
What do you make of the fact the the normalised Media Wearout Indicator is still 100 after being used every day, but off at night, since April 2013? Do you think that figure can be trusted?
Please keep in mind that the Intel® SSD 520 does not count power-on hours when it is in low power mode (standby), this is probably the reason why the Hard Disk drives show a higher amount of hours.
Regarding the Media Wearout Indicator, we consider it to be the best method to estimate the wear of the NAND chips. We are not aware of misreporting issues in this attribute of the Intel® SSD 520 Series.
It is worth to mention that the amount of writes is the main factor in the wear of the drive, if a system does mostly reads, then we would expect the SSD to have a longer lifetime.