iMac 27" late 2013 ssd portion of fusion drive smart status failed but still working...

Phillipwj wrote:

HWTech you're kind of closer to what I was really trying to understand, ie the way the iMacs internal SSD (as part of a Fusion Drive or split) interacts with SMART and tools like DriveDX and whether what I'm seeing in the reports is really the death of the SSD or just a glitch in the way such tools interact with these slightly different types of hardware in these iMacs. I've attached the SSD report here if that sheds any further light.

The SSD has written nearly 300TB in 10 years. Most consumer SSDs will have a lifetime TBW (aka TeraBytes Written) level of about 300TB although that does vary by the size of the SSD (smaller SSDs have lower TBWs) and also the quality of the NAND chips used in the SSD. Unfortunately Apple has never published those specifications, besides they would vary by SSDs since Apple used multiple SSD vendors for their SSDs.

Without the SSD providing more SMART attributes, there is no way to truly get an accurate analysis of the SSD. About all you can do is monitor the critical values that are left which are:

   1   Raw Read Error Rate                  
   5   Retired Block Count                  
 169   Total Bad Block Count                  
 197   Current Pending Block Count 

If you start seeing the RAW value increase (especially quickly), then it would likely be a sign of the SSD's demise due to the Wear Level Count being passed manufacturer expectations.

Like I mentioned most SSDs I've encountered while supporting my organization's computers were due to the SSD's controller failing or when the Host Writes attribute were in the PB range.

I was under the impression that if I run as Fusion Drive and either part of that dies (ie ssd or hdd) than you lose all the data (not that I haven't got it backed up, but still),

Yes, that is correct, but that is what backups are for.

and since it's a 120+Gb SSD I thought (before I opted for external ssd instead) I could maybe benefit from using it split using SSD for macOS System and HDD for data. That way if the SSD drive dies I've still got all the data in place on the separate HDD. I'd also benefit from a faster macOS system running on pure SSD than the hybrid Fusion arrangement.

Backing up becomes more complicated with this more complex setup especially when you go back to a single drive setup & try to restore everything.

So I'd be interested to hear why you think I should go back to Fusion? I guess it would speed up accessing the HDD , but would a Fusion Drive also place more or less stress on the SSD? I had picked up from somewhere that in the Fusion Drive arrangement the SSD gets absolutely thrashed as a buffer for all data being read/written to HDD too so it really gets clobbered a lot more than if it's just a separate SSD.

Remember it took 10 years to have the SSD write 300TBs of data with the Fusion Drive setup. If the Fusion Drive were kept, I'm not even sure whether the SSD or HD would wear out or fail first anyway even with the Wear Leveling attribute below manufacturer expectations (assuming the interpretation of the data is accurate). I'm leaning to the HD wearing out or failing first though since I've seen SSDs write PB's of data while I've never seen a HD survive for more than 60K to 80K power on hours (years ago 80K power on hours was likely sometimes even near 90K, but less so today).

I'm just trying to weigh the odds of the (I thought strange) SSD drive report and considering the risk of going back to using the internal drives, using the SSD for macOS and HDD for data , or maybe Fusion if there is actually a strong case for/advantage in doing that.

Since the Fusion Drive setup is no longer, it really depends on what you prefer to do. It is a lot of work to rebuild it if your current setup is working fine for you, or if you feel safer installing & using macOS from an external SSD.

If I were supporting this Mac for a friend or family member, I would have kept them using the Fusion Drive setup. After all, how much longer will this 10 year old computer remain relevant since macOS Catalina is the last supported version of macOS? It won't be long before you are either going to have to do a lot more work & research to keep it accessing online resources. Of course if your usage does not involve online resources, then that is not an issue. Just make sure to have frequent & regular backups (that should be the case anyway).

As with everything else, you should do what you feel is best for yourself. That is different for everyone. I'm sure most others here would advise you to install & boot from an external USB3 SSD if that helps.

Phillipwj wrote:

I forgot to say, macOS Disk Utility reports SMART Status on both SSD and HDD as Verified.

That would tend to imply that DriveDx (or rather the "smartctl" utility of the smartmontools open source project which DriveDx uses) is incorrectly determining the Threshold value for this Apple SanDisk SSD. Normally when the "Worst" value drops below a non-zero Threshold value, the drive triggers a SMART failure status that macOS would then show. Since macOS doesn't show a SMART failure, I would say this Wear Level attribute may not be failing.

Again, this is why I mention on this forum that SSD health reports must be manually interpreted. The notices that DriveDx brings up are just reminders to examine the SSD's attributes to see if there is a real issue to worry about. Hard Drives are different.....if DriveDx shows any "Warning" or "Failing" notices, then that means the Hard Drive is worn out or actually failing respectively. In my personal experiencing supporting my organization's computers for over 20 years, a worn out HD is just as bad as one which is failing. This difference just happens to be the difference between how HDs and SSDs work. There is no real good way to accurately have an app summarize an SSD's health, only alert to potential issues & changes.

You would have been better off leaving the Fusion Drive intact. SSD health is not as easily determined by the SMART health values......they really need to be manually interpreted...when you see a "Warning" or "Failing" status for an SSD's SMART attribute. Plus when an SSD's SMART attribute drops below the Threshold value to trigger a "Warning" or "Failing" notice in an app such as DriveDx, then you should just keep a closer eye on the SSD's SMART health attributes going forward. If you notice any other values declining (especially quickly), then it would be time to stop using the SSD. Many SSDs can go a lot longer than the manufacturer's estimated values suggest. I've seen several SSDs only fail after writing PB's of data (I'm sure their SMART health attribute dropped below the Threshold long before writing PB's of data).

Otherwise all of the other SSD failures I've encountered were due to the SSD's built-in controller which is not monitored at all and tend to occur quite suddenly many times without any warning signs.

With Hard Drives, it is completely different. If DriveDx shows a "Warning" or "Failing" condition for any attribute, then the Hard Drive should be replaced.

If Disk Utility is not showing a "SMART status failed" condition for the SSD, then you should be able to continue using the SSD, however, if Disk Utility is showing "SMART status failed", then you won't be able to reinstall macOS onto it as the installer won't let you.

Phillipwj wrote:

This is apparently due entirely to the Wear Levelling Count:

Current Value 80

Worst 80

Treshold 100

From the above figures it somehow then calculates 0% Life left, which to me seems somewhat obscure, as 80 used out of 100 used surely suggests 20% left?

Some of the SMART attributes start at 100 and go down to 1, while some other attributes may start at 200, or even 254. Notice the Threshold of 100, if the starting value was 200, then the "worst" value dropped below the Threshold which triggers the drive's SMART failure status (it won't trigger if the Threshold is one since the Current/Worst values never drop below one and are usually considered LifeTime health attributes which means a failure is not necessarily imminent).

I'm wondering whether anything seems strange about these stats with the Wear Levelling standing alone as the only issue and/or considering the drive seems to be working fine, and also that macOS's own Disk Utility mentions no problems at all, in even says the SSD's SMART Status is Verified, could this be some sort of misreporting by DriveDX?

PCIe based SSDs tend to handle the SMART information a bit differently even when they are SATA based SSDs.

DriveDx is reading the Value, Worst, and Threshold values and interpreting them as they should be interpreted. It is always possible the SSD just is not providing proper information, or used a different method. Drive manufacturers don't really seem to care much about standards or providing documentation.

Could the SSD in fact have a good reserve of life left in it yet considering the actual value of 80 and not 100, it just seems to have stopped counting at 80 and given it 0% score.

Probably. Unfortunately most SSDs these days only have a few basic health attributes unlike the older models that had dozens of attributes which showed different aspects of an SSD's health. Manufacturers just don't care.

At this point, I would be leery about using either of the 12+ year old internal drives.

I would keep everything together on the one external SSD and run from it.

Then I would backup that external SSD to a second external SSD or HDD.

It is a waste of time and money trying to repair a 12 year old iMac.

Run it from the external SSD while your shopping for a new iMac or Mac mini.

den.thed wrote:

It is a waste of time and money trying to repair a 12 year old iMac.

Run it from the external SSD while your shopping for a new iMac or Mac mini.

If budget is a consideration a new Mini would be the most economical route to go. You can get an M4 Mini with 16 GB RAM and a 1TB SSD with a 3rd party 27" or 32" 4k monitor for $300+ for less than a new 24" iMac would cost.

+1 to what @den.then has posted.

I love my own 2013 27" iMac, but I know that with each year that passes it becomes less capable to provide productive use. I can continue to use apps that are already installed, but the OS is unsupported, secure internet access is waning and the hardware is twelve years old and failure potential is increasing. I did replace the internal drive with an SSD five years ago, but I can't say I'd do the same today. In fact, early last year I bought a MacBook Air M2 that has pretty thoroughly replaced the iMac as my daily driver.

The old iMac is now only a media server and resource for vintage/obsolete OS troubleshooting for this Community.

Phillipwj wrote:

👍 I've been pretty leery up to now. Reckon I will remain so.

Also have multiple backups of the important stuff all over the place so that's no problem.

Good work, better to be safe than sorry.

Sadly time is running out for the old girl and sooner than later it will need to be replaced.

Again, "Run it from the external SSD while your shopping for a new iMac or Mac mini"