iMac (Retina 4K, 21.5-inch, 2017) really slow

Welcome!

Your USB 3-equipped Mac with a hard disk can have improved system performance by connecting to an external solid-state drive (also known as an SSD). An external SSD as your startup disk can give your Mac additional performance for system responsiveness, apps, startup, and more. An SSD will make your Mac 10 to 40 times faster for storage, and in turn, make your entire Mac faster and more capable. To learn more, see Use an external SSD as your startup disk with your iMac or Mac mini - Apple Community. 

Additionally, I'd recommend that you delete the Memory Clean 2 application and create a Time Machine backup.

Jack

It seems that your Fusion drive (the HDD portion) if failing by the very low read and write speeds:

Write speed: 61 MB/s

Read speed: 77 MB/s

I wholeheartedly agree with Jack-19 that your best option would be to get an external SSD, clone your current drive to it with Carbon Copy Cloner (it might take some time), and boot and run from the external SSD.

If you go that route I recommend you contact Customer Support at OWC (MacSales.com) and get their recommendation of which of their external SSDs would best fit your Mac model, work requirements and budget.

If you go that route and still want additional RAM you can get a couple of 4 GB modules to raise the total to 16 GB from either OWC or Crucial.com. I wouldn't get it from any other vendors.

Are there any solutions for this? I have a friend who has a 2017 iMac with a 1TB hard drive, which only uses less than 256MB, but it is so, so slow> Any suggestions to at least get it to less than 10 seconds between mouse clicks?? Thanks!

kc2101 wrote:

Are there any solutions for this? I have a friend who has a 2017 iMac with a 1TB hard drive, which only uses less than 256MB, but it is so, so slow> Any suggestions to at least get it to less than 10 seconds between mouse clicks?? Thanks!

If it has an internal hard drive (mechanical) as does the Mac of the original poster, it will always run very slowly with an internal HDD formatted as APFS. APFS is the more recent file system format that is optimized for solid state devices (SSD) but is very slow on mechanical drives. The only solution is to replace the internal drive with an SSD or do as Jack-19 suggests and use an external SSD instead of the internal drive.

If the internal drive is an SSD, then more troubleshooting is needed here.

Hi,

Seems you are using Adobe suits as well as Dropbox on your iMac with only 8GB RAM.

You'd better upgrade RAM at least 16GB, PC4-19200 SODIMM(8GBX2).

I recommend you start your own topic, give the details of the Mac and post the results of an Etrecheck report. Then you will get undivided attention from those who offer potential solution.