My late 2015 iMac recently started taking a very long time to go from the startup chime till the Apple logo appears - about 2.5 minutes. Between the chime and the logo, the screen was black.
After resetting SMC and PRAM, I traced it to an external USB-C SSD, but in the course of narrowing things down I noticed that the "time to Apple logo" varied somewhat depending on what was plugged in, for example:
- no USB devices plugged in: ~6 secs
- only external hub plugged in (no additional devices): ~8 secs
- only external USB3 HD plugged in: ~9 secs
- only external USB3 SSD plugged in: ~20 secs
- everything plugged in (except USB-C SSD): ~22 secs
- only external USB-C SSD plugged in (with supplied USB-C to USB-A cable): ~150 secs
Is there any guidance on what is normal and expected for "time to Apple logo", and why the variation between different USB3 disks, let alone the exceedingly long time for the USB-C SSD?