iMac slowing down

Neil P wrote: The projects are unrelated. It's a Fusion Drive so half SSD (if that makes sense ?)
Is Black Magic Disk test a free download ?

Neil

Well, not "half" SSD... more like roughly 1/30 SSD, and read/write performance may vary wildly. I'd say the typical results should be significantly below what the BMD test showed you. Mind you, when running BMD one can tweak the size of files it reads and writes. I don't have a Fusion Drive to test, but as your media grows, the proportion that comes from the SSD part will decline and performance will too.

lichinho wrote: .. read/write performance may vary wildly. I'd say the typical results should be significantly below what the BMD test showed you...I don't have a Fusion Drive to test, but as your media grows, the proportion that comes from the SSD part will decline and performance will too.

I seriously doubt it's the Fusion Drive causing this. I've had a 2013 and 2015 iMac with 3TB Fusion Drive and at 1/2 full the I/O performance is very good.

He's seeing a beach ball for several minute period on FCPX startup -- when only using I have a small project in (I think) a small library. That's not normal.

He needs to trash prefs, copy the small project to a separate test library, close all other libraries, disable background rendering, restart FCPX then re-test with that configuration.

If there's any chance he's imported "bare" AVCHD .MTS files using "leave files in place" that can cause severe I/O problems. Maybe he can answer does he have any AVCHD content imported this way.

Except for that it seems very abnormal and usual. As stated before he needs to strip all effects from the test project to ensure those aren't involved. In a few cases 3rd party plugins (even if not used in the timeline) can cause performance problems. Probably the fastest way to evaluate that is back up the system drive using Time Machine or Carbon Copy, reformat the machine and re-install macOS and FCPX, load the stripped-down test library and test it. If it still happens, it's not 3rd party plugins, system extensions, etc., and he can restore the original image from the backup. Or alternately just leave it clean and install each app/plugin he wants. It's a good idea to do that periodically anyway.

I'd also suggest he ensure he has Apple Pro Video Formats loaded: support.apple.com/kb/dl1947?locale=en_US

During such testing it's good to have everything disconnected from the iMac such as video interfaces, extra hard drives, hubs, etc. In some cases those if malfunctioning can generate a stream of interrupts or errors that slows down the entire machine.

One common error source is the driver software that comes with X-Rite i1DisplayPro screen calibrator. It can silently crash repeatedly, slowing down the machine. This isn't documented by X-Rite. There's an undocumented procedure they'll walk you through on the phone to delete certain files to stop this. I really think Apple should warn them and the user community to not distribute or use that software until they fix it. Anyway, that' s just one example.

Thanks for the detailed reply, I'll digest all this.

The computer has actually been working better today. I've turned my two hard drives off (a Lacie which is half full and a drobo which is very full) and things seem to be better, though the footage that I am using is on my desktop.

Doing re installs does song very scary but if the problem does continue I'll have to bite the bullet.

thanks

Neil