Technical Q on Mac OS shutdown sequence

This question is not related to any specific issue, only a Mac OS curiosity resulting from the daily shutdown of a Mac Pro 6.1 and how to guess or figure out what is going on internally during the process. ‘stop. Read more if interested.

Why? The 6.1 is connected through a few of its TB2 ports to two LaCie drive bays and one Drobo drive bay, as well as a LaCie 8TB external drive used as a TimeMachine and three Apple 27 “displays – the old ones are not. After starting “shutdown”, I usually look at the blue light of the LaCie TM’s drive activity using it as a monitor of the shutdown process status, which can take up to at a minute or a little longer. I usually don’t leave the Mac until it’s completely shut down; I don’t know how to call it one of those compulsion disorders that need to be ended at the end of a day from work, or an unfounded paranoia about the shutdown sequence not ending after I leave (I had this problem for a while; solved a long time ago).

Shutdown ends after the LaCie TM’s blue drive activity light turned off the last time, after flashing intermittently (no pattern) for approximately one minute that the machine is in its shutdown sequence. I make sure that when I start shutdown it doesn’t interrupt any backup that is in progress or about to start. Once the shutdown procedure has started I know it is about to end every time when the LaCieTM blue light flashes for the last time, turns off, then all 3 displays turn off at the same time , the blue lights on both LaCie bays blink and go goes off and finally the Drobo drive bay LEDs turn off and the Drobo goes to sleep. Everything is off or in the case of the Drobo, in standby (sleep).

The question: what happens during that minute of downtime? When the LaCieTM LED starts blinking and blinking, it looks like it is checking and possibly saving snapshots of the other drives (the native Mac SSD, the LaCie bay (two volumes) and the Drobo (two volumes)) , then finally shuts down, triggering the Mac itself to complete its shutdown sequence, which it always does when the blue MT light finally turns off and the external drive shuts down. The point is, the TM is not configured to back up anything other than its default Macintosh HD boot volume, but it seems to monitor shutdown until it is complete. Is anyone technically adept enough to guess?

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Brian Steele

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