Computer takes a very long time to boot since upgrading to Sequoia. Main application used is ProPresenter, which has been very slow and has recently seemed to freeze the entire computer to the point that I can’t even get the mouse to the Apple logo.
iMac 21.5″, macOS 15.3
The HDD probably isn't going bad, but MacOS has been optimized almost exclusively for SSD use since Catalina was released late 2019. Believe it or not yours is one of the fastest 2.5" HDD performance reports I've seen in years.
While you could replace the internal drive with an SSD, I would instead suggest reinstalling MacOS onto an external USB 3.1 or 3.2 SSD and configuring that to be your startup drive. If performance is still not fast enough with an external SSD you can reuse the drive as generic additional storage with a newer model.
Install macOS on an external storage device and use it as a startup disk - Apple Support
Also +1 for having a timemachine backup. Those are always a good idea.
I would get an external SSD and make it a clone using an app like Carbon Copy Cloner and use as your main (boot) drive. Then the internal drive will not be an issue. The fastest would be an external thunderbolt drive in a proper enclosure. On my 2019 iMac I use a WD SN850X NVME drive in an Acasis TB enclosure and it works great.
Well the primary problem is you bought the most basic iMac that was ever made, the 21.5" models that have glacially slow 5400 RPM HDs installed. That is the main bottleneck to an otherwise capable computer. It is also now 6 years old and may not be in good health.
That being said before you do ANYTHING please backup the computer as your data is at severe risk and if the HD is failing you will lose ALL of your data!!!!!!!!!!!!!! There is ZERO reason to not backup the computer daily using Time Machine which is pre-installed on your Mac, all Time Machine requires is an External Hard Disk such as the OWC Mercury Elite Pro series. A 2-4 TB External Hard Disk is recommended!!!
After you have the External Hard Disk please read Back up your Mac with Time Machine!!!!!!!!!!!!!!!!!!!!!!!!!!!!
After. you have backed up the computer leave the External Hard Disk connected and Time Machine will backup regularly.
THEN AND ONLY THEN you can begin addressing the issue you posted about. What I would recommend is that you run a DriveDX report and if the HD shows ANY errors then your HD is failing and MUST be removed from the equation.
If you decide to keep the computer the easiest method of adding an SSD is going with an external SSD. Here are detailed instructions for doing so:
How to setup an external SSD as your startup disk
Not all external SSDs are the same so it's important to get a quality and fast drive. The one I'd recommend for your computer is :
https://eshop.macsales.com/item/OWC/TB3ENVPFX01/
If you need additional storage the 2TB version of the same is only $20 more right now which makes it a great buy.
Thanks! Will get an external drive and set up for Time Machine back-ups as a first step. If this HD is going bad, can I replace it with an SSD? or would it be better to relegate this to a browser host and get a newer model?
2019 iMac booting slow after installing Sequoia
