Upgraded late 2013 21.5” iMac to Sonoma

Today I successfully upgraded a late 2013 21.5” iMac with 8GB RAM using open core to install Sonoma.

The iMac had an internal 1TB HDD that was running like a slug. I did not want to spend money to buy the iMac upgrade kit so opted for a $11 Sabrent external drive enclosure (EC-UASP) and a $50 Samsung 500GB SSD.

In retrospect, it would have made life easier to upgrade the internal HDD. The iMac did not like having 2 USB drives plugged in at same time when you hold control key on boot up. So I had to plug the USB drive in first, press control key on boot up, wait, then plug in the external SSD drive.

Since Sonoma install required about 5 reboots, I had to repeat the process 5 times. When it’s all said and done the iMac booted Sonoma from the external SSD drive and run just fine. Was able to restore data (migration assistant) from Time Machine backup.

Although the external drive enclosure is advertised as UASP, I don’t think it’s running in UASP mode from sys info.

Since the system did not like 2 USB drives plugged in at startup (it will default to booting from internal HDD drive), I partitioned the internal 1TB HDD to make a 500GB backup partition for Time Machine backup. Seems to work well.

Using black magic disk speed test, the SSD in external enclosure does about 420 mb/s read/write. Catalina ran fastest from the SSD, but Sonoma’s performance is very acceptable.