SSD health -- the Rated Lifetime Used

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SSD health -- the Rated Lifetime Used

Postby jdlk » 2012.02.01. 17:42

I am trying to understand the health rating for my SSD (50 per cent). It is a 64GB 2.5" Crucial RealSSD C300.

The health value is apparently determined by S.M.A.R.T. attribute #202 Percentage Of The Rated Lifetime Used. Other than this value, HDSentinel reports that 'The status of the solid state disk is PERFECT. Problematic or weak sectors were not found.'

Based on the "vendor-specific values" for Rated Lifetime Used, the health rating for my SSD is due to reach zero in September this year, less than two years after the disc was first used (Jan 2011). Yet Crucial offer a five-year warranty on their SSDs...

What exactly does this rating mean? Is the rating a real-time value based on actual usage? Does it reflect actual risk of failure? I can't find a discussion of this in the help file.

Also, in the help file, SMART attribute 202 comes up as '202 Data Address Mark Errors'. Am I looking at the wrong information table?
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Re: SSD health -- the Rated Lifetime Used

Postby hdsentinel » 2012.02.02. 15:46

Thanks for your message. In general, the manufacturer for most SSD devices define a method to measure the overall "health" of the memory cells in the SSD.
Usually there is a special attribute (for example, #202 Percentage Of The Rated Lifetime Used in your SSD) shows the calculated value, in this case 50%.

Hard Disk Sentinel constantly analyses the working parameters to detect if there's any error / problem with the device, but if there are no such problems found, the health of the SSD is still decreasing (as you can see) due to the actual usage.

It would be really nice to know HOW exactly this value calculated (yes, it is surely calculated by real-time usage statistics internally in the device) - but the manufacturer does not really make this information public. We all know that it is surely related to the amount of written data to the SSD (as write operations cause wear to the memory cells and reduce the health of the device - so it is important to minimise writes) - but it would be nice to know how exactly this value calculated.

In general, Report menu -> Send test report to developer option always helps. Periodic reports (especially when the displayed health changes) are the most valuable as then it is possible to check what other information and S.M.A.R.T. attributes change and verify the amount of written data (if the SSD has proper attributes to measure written data OR by using the write statistics displayed on the "Performance" page).

Sorry for the confusion: the help discusses the hard disk (HDD) specific S.M.A.R.T. attributes only.
As many of them are related to mechanical parts, they are not applicable for SSDs.
This is why SSD manufacturers decided to use the same attribute ID numbers - but with different meaning - to check the status of their devices.
So it is important to properly identify the type of the SSD, the SSD controller chip used in that and the proper meaning for the corresponding SSD.
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Re: SSD health -- the Rated Lifetime Used

Postby jdlk » 2012.02.02. 20:19

There still seems to be so much confusion surrounding SSD longevity. There are many people suggesting that the latest generation of SSDs, including the Crucial ones, should outlive the average standard HDD (provided you use TRIM, which I do).

My SSD is purely used as an OS disc. I write all data to a separate HDD, and I try to make sure that any program which writes lots of data to log files, etc, does so to the HDD. And I have 8GB of RAM, so swap file usage should be minimal (official advice now seems to be that if you have lots of RAM, you should leave the swap file on the SSD).

So I have a modern SSD and I follow all the recommended usage guidelines, yet HDSentinel suggests my SSD will have a health rating of 0% within 21 months of first use. That does raise questions. Will the zero health rating enable me to return the SSD to Crucial under the five-year guarantee? Or is the SSD health rating only a theoretical guideline with no real impact on the actual risk that the SSD will fail?

In short, what does 'Percentage Of The Rated Lifetime Used in your SSD" mean in practice? Is it something to be worried about, take action on, or should I just ignore it? For those of us who rely on HDSentinel to predict disk failure, these are important questions.
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Re: SSD health -- the Rated Lifetime Used

Postby hdsentinel » 2012.02.03. 11:12

Personally I completely agree that there are lots of confusion about SSD longevity / endurance - even at the manufacturers.
In practice, SSDs are really new devices to say anything about how they would work in long (really long) term of usage, eg. how they would perform after 3-4 years (or even more - which is still under the warranty period).

jdlk wrote:My SSD is purely used as an OS disc. I write all data to a separate HDD, and I try to make sure that any program which writes lots of data to log files, etc, does so to the HDD.

This is perfect as these steps should really increase SSD lifetime.

jdlk wrote:And I have 8GB of RAM, so swap file usage should be minimal (official advice now seems to be that if you have lots of RAM, you should leave the swap file on the SSD).

This is true _only_ if you have configured Windows to use a fixed size swapfile. Otherwise Windows constantly tries to allocate / deallocate size and this may cause extremely high write traffic.

You may check on the "Performance" page the amount of data written to the SSD and the real-time performance information (eg. current amount of writes / daily amount of writes) to see how much data is written, even in idle periods.

jdlk wrote:So I have a modern SSD and I follow all the recommended usage guidelines, yet HDSentinel suggests my SSD will have a health rating of 0% within 21 months of first use.

Not really. As I tried to explain, this % value is calculated _only_ by the manufacturer and reported by the SSD.
While Hard Disk Sentinel collects all information and reports errors (if any found) it only read and report this % value but has no control over it.
With other words, the manufacturer suggests that the condition of the device decreases.

jdlk wrote:That does raise questions. Will the zero health rating enable me to return the SSD to Crucial under the five-year guarantee?

Because this value is determined by the manufacturer, only they can answer to this question.
Personally I feel they may not give replacement because of two different reasons:
1) this attribute (Percentage Of The Rated Lifetime Used) is a statistical one, it does not directly determine the health.
Several attributes for this SSD directly determine the health as they would report errors. If it would happen, the manufacturer should immediately replace the drive of couse.

2) the "surface" (memory cells) are still working even if you reach the end of the rated lifetime. According the tests for SSD endurance, at this point the SSD may still seems usable, just may perform slower compared to a new device - and may not be able to retain the stored information for a longer period.

For example, if you perform a surface scan (Disk -> Surface test -> Read test) you can check the current read speed - and you can compare it with a future results, eg. after 1 year of usage. (write speed may be an other question also).
Or - if you fll the SSD completely and put it on the cupboard, you may not be able to retrieve the stored information after some inactivity time.

These both may risk stored data, and this is why it is important to monitor the device.

Anyway, personally I feel it is possible that there will be a warranty replacement (I suspect the manufacturer calculated the high price of the SSD considering this replacement also).

jdlk wrote:Or is the SSD health rating only a theoretical guideline with no real impact on the actual risk that the SSD will fail?

I'd say yes, this is a theoretical guideline only - but due to the wear of the memory cells, data loss may occur any time when this level is reached.
The SSD (eg. after a complete reformat / reinstall) may still work, just slower and/or without keeping the stored data for longer period.

jdlk wrote:In short, what does 'Percentage Of The Rated Lifetime Used in your SSD" mean in practice? Is it something to be worried about, take action on, or should I just ignore it? For those of us who rely on HDSentinel to predict disk failure, these are important questions.

Maybe the above answered these questions.
If you prefer, please use Report -> Send test report to developer option, then I can examine the complete status of the SSD and may advise.
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Re: SSD health -- the Rated Lifetime Used

Postby jdlk » 2012.02.03. 20:49

I appreciate the detailed response, which is helpful. Many thanks.
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Re: SSD health -- the Rated Lifetime Used

Postby nimbystripes » 2012.11.17. 03:26

I agree. Information found here helped me a lot.
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