2017 iMac 21.5inch 1TB HDD entry level iMac.

[holty]

This unit is too slow, can I connect a USB SSD and boot via one of the 4 USB ports and expect an improvement in speed, rather than going down the take apart route.
Thanks, Holty

 

[jerwin]

Sure. I replaced my imac 5k's fusion drive with a USB enclosure + 1 TB SSD. It's much faster now. You might run into some problems with TRIM, or SMART, though.

 

[redfirebird08]

Yes, you can absolutely connect an external SSD and use it as your boot drive. Try Carbon Copy Cloner to make a bootable copy of your internal drive. It's about $40 to buy Carbon Copy Cloner, but they have a 30-day free trial that will get the job done if you only need to make a single copy and be done with it. After you get everything copied into the external SSD, change the "Startup Disk" in System Preferences on Mac OS. Then restart the computer and it will run everything through your external SSD. Should be a huge improvement in speed compared to using that crappy old spinning drive for your daily tasks.

Another option if you want extreme speed is to get a Thunderbolt external SSD drive with PCI Express. This will be faster than USB external SSD drive with SATA. The USB SSD drive will run maybe around 400-500 megabytes per second. This is great compared to a spinning drive at less than 100 megabytes per second. But a Thunderbolt drive with PCI Express can run at 1,500+ megabytes per second. I just setup one myself on my 2017 iMac and I'm clocking around 2,000 megabytes per second. Below is a link to the drive I bought. It will work with your 2017 iMac:

VisionTek 1TB Thunderbolt 3 Portable External SSD, [Intel Certified], Bus Powered, MacOS and Windows Compatible (NOT Compatible USB-C) - 901196

Engineered for long-term real-world use, you’ll experience speeds up to 1600 MB/s, up to 100x greater data reliability than a costly Enterprise Class HDD, and access times up to 15x faster than a conventional HDD. 40Gbps Thunderbolt 3 Interface—Connects to any Thunderbolt 3 computer port, or at t...

www.amazon.com

1 terabyte version is $180 and 512 gig version is $105. That's pretty damn cheap considering the speed this thing delivers!