Hi all, I have a late 2015 21.5 inch iMac and last week I noticed the 1TB HDD was louder than usual, it seemed to be churning way more than usual. I opened up disk utility and ran First Aid, this reported the drive as having no issues. I then downloaded SMART Utility and low and behold the drive status was showing as "Failing". The exact reason was 'reallocated sector count = 21'. To verify this, I downloaded DriveDX and this too reported the exact same error (although oddly it also gave a green light for both drive health and performance - 79% for performance to be exact) I contacted Apple support as I have 6 months AppleCare remaining and told them the results of the two utilities. I was asked to run their diagnostic tool which came back as ADP000 - No issues found. Due to this, they were not interested in granting a replacement for the drive. Instead of sitting here waiting for a drive to fail, I took some advice from here and bought an external 500GB Sandisk SSD drive. As per the instructions, I re-installed Mojave but this time pointing it to the SSD rather than the HDD and the result is mind-blowing, it feels like a new machine and with the bonus of not hearing any HDD noise. I'm liking it so much that I'm tempted to keep things this way longterm, but with the OS literally being run from a drive connected via a USB 3.0 port, am I potentially putting any more damage/strain on the iMac, with everything now constantly being written/read through the USB to the drive?