SSD of 2TB Fusion Drive failing

par4uk wrote:

Have 27" 2TB iMac 2019 running Big Sur. SSD shows 10% life remaining and falling. What happens when it falls to zero? Will my iMac still work?

It really depends on what this attribute actually means. How are you reading the SSD health? Post the complete health details for the SSD so we can see everything. Most times when the SSD's health attributes reach the end you will want to stop using the SSD. In theory when an SSD reaches its end of life the SSD is supposed to enter into read-only mode, but unfortunately this rarely happens and all data on the SSD is lost/inaccessible.

Make sure to always have frequent & regular backups.

Just had to replace the 2TB HD at Apple Store as it failed (same machine) but they would not replace the entire Fusion Drive. Have Time Machine backups. Can I install the TM backup on an external SSD and use it as my startup drive? Thank you. Phil Richardson

Yes, but you cannot use the external SSD as part of a Fusion Drive.

Run DriveDx and post the health report for both the SSD and the Hard Drive here using the "Additional Text" icon which looks like a piece of paper. DriveDx will provide the full health information of the drives in a format I am familiar with. I'm not sure Micromat will provide the full information.

Thanks for the reports. Unfortunately I haven't paid a lot of attention to the specifics health attributes on the Apple SSDs so I am not completely certain with their behavior. The SSD vendors don't always publish specific details (or the details are difficult to locate).

I see that Attribute #5 "Life Percentage Used" is considered to be 13% at the time of the report was made meaning 13% life is left on the SSD. We are assuming the starting value was indeed 100 which is common, but not guaranteed -- seems like it started at 100 since 87 + 13 = 100, but most attributes are not that linear between "Value" and "RAW value". Unfortunately I don't know exactly what this value is supposed to represent as there are many things which can be used for an "estimated life". Unfortunately this mystery is common with SSD vendors with each vendor using their own secret indicators. It is harder to judge this value without knowing the starting conditions for all the other health attributes or how much the various attributes are changing in respect to one another. The closest information I could find is this Reddit thread regarding a non-Apple Samsung SSD estimated life left. In this thread there is one post showing an SSD at 156% used and the OP in that thread mentioned some Samsung SSDs going 2 to 3 times past their listed life (there is link to reference so no idea which SSDs are being referenced).

https://www.reddit.com/r/DataHoarder/comments/cxb1hf/does_anyone_have_a_samsung_ssd_or_nvme_drive_well/

Attribute #5 "Life Percentage Used" as well as most of the other health attributes on this SSD are considered "Lifetime" health indicators which have no actual number (aka Threshold) set for alerting to a failure indicated by the "zero" for the Threshold. This means these values are what the manufacturer has estimated to be the working life of the SSD, but the drive may continue working well past these attributes reach a RAW value of one.

Without knowing the specifics of the NAND used in the Apple Samsung SSD it is hard to know how much data can be written to this SSD. You have already written about 200TB to this SSD's NAND memory cells which have a limited number of writes available. I'm surprised that the "Value" column for Attribute #7 has not decreased from the 100 starting value. To me this indicates this health attribute (and perhaps some of the others) may not be properly configured by the drive manufacturer. Most SSDs have a lifetime write value (TBW) between 300TB to 3,000TB depending on the SSD (type of NAND memory, size of SSD, size of NAND blocks, etc.).

Unfortunately most SSD vendors do not provide enough information in their SMART reports which would help us to understand the condition of your SSD. It is also possible that this attribute is not named correctly which is somewhat common. It is a shame these vendors don't provide full information or implementations of health reporting. In fact each SSD vendor names and numbers their attributes differently creating even more confusion instead of agreeing upon a standard for commonly shared attributes. At least the hard drive vendors tended to follow a standard at least for the most important attributes.

In order to figure things out you would have to monitor the changes in these SMART Attributes (aka health attributes) to see how quickly the Lifetime Remaining value is decreasing compared to the data written to the SSD (attribute #7).

I believe I have one Apple 2.5" SATA SSD that is reporting an end of life condition, but I haven't had time to test it to see if it is still working correctly. My Apple SSD still seems to be working though. It is one of only a few SSDs that I've seen near its end of life (or it may be the only one I've seen). I know we have a few SSDs that may be starting to get near their end of life (a year ago), but with the extreme workload during COVID this year I haven't had time to check these other SSDs to see if they have reached these conditions or how they are working. My supervisor wasn't concerned as he was planning on getting some new computers, but I don't think that has occurred yet.

Make sure to have frequent & regular backups of your data (always good advice -- multiple backups/copies). This is even more important when using an SSD (any SSD even a brand new one) since it is impossible to recover accidentally deleted data from an SSD plus an SSD can fail at any time without any warning signs. Most of the SSD failures I've seen have been very sudden failures where a professional data recovery service would be needed to attempt to recover data from the SSD. When the SMART health Attributes indicate the SSD may be nearing its end of expected life having a verified working backups are even more important than ever.