iMac (Late 2012) Performance Issues : External SSD via TB2?

iMac (21.5-inch, Late 2012) Performance Issues :

I have a late 2012 iMac(21.5-inch) with 3.1 GHz Quad-Core Intel Core 7 Processor, 16 GB RAM, 1.12TB Fusion Drive running macOS Catalina Version 10.15.7 that works reasonably well, but more and more frequently is taking a LONG time to start up, shut down and depending on use is also locking up. I can see no specific issues with the HD and have tried many maintenance type tasks from eliminating unused apps to using the CleanMyMac application etc. So, I am looking for other options to improve the situation before a replacement. Could an external SSD that I can connect via the Thunderbolt 2 port be an option, if so what would be a good buy ?

Thanks for any suggestions!

iMac 21.5″ 4K, macOS 13.7

Posted on Jan 18, 2026 8:36 AM

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Daviedic Author

Level 1

4 points

Posted on Jan 24, 2026 9:06 AM

EtreCheck report

Volumes : Macintosh HD Device - Path : /dev/disk1

Volumes : Macintosh HD - Device Path : /dev/disk0

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17 replies

Daviedic Author

Level 1

4 points

Jan 25, 2026 2:28 AM in response to den.thed

Firstly, Thankyou for your suggestions etc... Have now removed the Avira-ware etc.

Ran EtreCheckPro and performance stats show an improvement:

System Load: 1.88 (1 min ago) 1.17 (5 min ago) 0.54 (15 min ago)

Nominal I/O usage: 10.61 MB/s

File System: 19.24 seconds

Write speed: 200 MB/s

Read speed: 426 MB/s

den.thed

Level 10

91,732 points

Jan 25, 2026 8:01 AM in response to Daviedic

That is good news, you're welcome.

Those Write/Read speeds are a lot better, but still slower than normal which is to be expected for the age of that hardware. Plus keep in mind that those Write/Read speeds may degrade to the slower speed with use.

If they do degrade, then running from an external USB 3.0 SSD will get you somewhere around 460 to 500 MB/s.

iMac (Late 2012) Performance Issues : External SSD via TB2?