Installed hardware with no issues. Unable to Erase (Format) the drive so I can’t install System. Removed SSD and connected via USB to MacBook Air (2014)…Formatted without issue. Reinstalled in iMac…saw it this time but would not install Backup and after that wouldn’t see it anymore. Is this a firmware issue?? Thanks.
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Details: As shipped, these models only supported the 3 Gb/s SATA II standard for both a 3.5" hard drive and a 2.5" SSD. However, as first discoveredby OWC, the iMac EFI Update 1.6, released two days later, quietly provided 6 Gb/s SATA III support.
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What is the macOS release your MAcBook Air is running and what was the macOS release your 21.5" iMac is running.
You maybe hitting a firmware/OS file system issue as Sierra and older OS's used HFS+ and from High Sierra onward is now using APFS and the systems firmware needs to be updated to boot from an APFS drive.
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