Modern hard drives keep track of their health, temperature, power-on hours and other important reliability statistics using a technology called Self Monitoring Analysis and Reporting Technology (SMART). By looking at the SMART data from a drive, you can predict if the drive is going to fail, based on its history.
Apple is neglectful at looking at SMART data and warning the user about a disk in dire health. This Pollyanna approach is dangerous because it gives users a false sense of security about hardware which is likely and prone to fail.
Apple’s Disk Utility program (on every Mac in the Utilities folder) will often report the SMART status of a failing drive as “Verified”. If you look at the actual SMART data, the drive is VERY clearly in the process of failing. For example, here is what Disk Utility says about an extremely sick external Time Machine backup drive’s SMART status:
Yet, if you look at the actual SMART data for the drive (I use a program called DriveDX from Binaryfruit.com), the drive has recorded some very serious errors (yellow and/or red are bad), indicating the drive isn’t healthy, is unlikely to allow restoration of files and should be replaced:
In addition to the danger of Apple not proactively warning users of a failing disk using SMART data, they also choose not to notify a user when data being written to a Time Machine backup fails. This leads to a false sense of security in regards to the backup of what may be the only copy of a user’s important data.
For this reason, I highly recommend backing up with a program that will notify of any read or write errors on the source or destination drive. I’m a fan of Carbon Copy Cloner from Bombich software because it will warn the user in the event that it can’t read or write data successfully.
Do NOT rely on a single Time Machine backup of the data on your computer.