Is my Mac’s Fusion Drive failing?

QMy iMac has an Apple Fusion drive, which I’ve checked using DriveDx. The Wear Leveling Count on its SDD part has fallen below 50%, although it’s little more than a year old. Is my SSD failing?

by Richard Champion

AThere are difficulties in estimating the life expectancy of SSDs. The SMART indicator of Wear Leveling Count (173) should indicate lifetime, but some SSDs don’t give accurate values, or they don’t change linearly over time.

Another way to check whether the SSD is wearing out is to look at the total data written to the SSD, reported in indicator 175 (Host Writes MiB). Convert that figure to terabytes and compare the result with an estimate of total write capacity, obtained by multiplying the SSD capacity in gigabytes by 5000. For example, a 121GB SSD should accommodate over 600TB of data being written to it before write failure starts to become likely.

Apple doesn’t put much trust in third-party monitors such as DriveDx, despite their sophistication and value, preferring its own hardware testing tools and those built in to Apple Diagnostics or Apple Hardware Test.

If you experience errors with your SSD, invoke any warranty or AppleCare remaining and hope it results in a replacement.

DriveDx provides detailed insights into SMART status indicators, but interpreting the results in terms of expected lifetime is not so easy.