iMac boots quickly but takes loooong time to log into account I do have a pretty good iMac (Retina 5k, Late 2014, 4GHz Intel Core i7, 32 GB RAM with a 3 TB Fusion Drive) running the latest stable macOS Sierra. When powering on, the log on screen appears pretty fast. But when I entered my credentials, the mac takes about 10 minutes until it's usable. I can click on windows before, they react after a long time, but I hear the hard drive for ~ 10 minutes and only after that the mac is really usable.

What could be the cause for this? I'm sure this isn't normal as my MacBook Pro is much, much faster (although there's an SSD, not a fusion drive).

What could I do to find the cause? Maybe the Fusion Drive is messed up?

EDIT:

I just found that disk0s2 is my rotational disk, disk1s2 is my SSD, I found screenshots of the storage system report which show it exactly the other way round... may that be the problem?
I've seen this before, but it could be a number of things. My suspicion is something in your Login Items is using a lot of CPU/Disk/Network thus delaying everything else.

To further diagnose run System Preferences from the Apple menu and choose Users &amp; Groups and create another account with any name you like. Log out, then log in to that account. Note how long it takes. If this is significantly faster, it's a user account issue for your primary user account, rather than a machine issue.

Machine Issue


Look in Activity Monitor in the Energy tab. This will show any applications that are using, or have recently used, a lot of resources. Sort by Avg Energy Impact. Anything obviously using more energy than everything else at the top of the list?
Run Anti-Virus scan; Clam XAV is in the App Store and free. Other free options are downloadable. Did it find any malware?
As an Administrator (if you're not already), run the Console app and enable 'Activities'. Does the console fill up with busy work? Anything dominating the output more than others?
See also:
speedup macOS Sierra startup, Troubleshooting Slugglish Post-desktop Startup


User Account Issue:


Run System Preferences: Users &amp; Groups. Choose your user account in the top-left corner (if not already selected) and then click Login Items. Do you recognise all of the items? Please note them down for later review. Some are system-provided (e.g. SpeechSynthesisServer) but IIRC it's okay to remove them all if you're unsure. Try this then reboot - did it make a difference?
See also: Troubleshooting Slugglish Post-desktop Startup