What is node doing right after startup (Heavy Disk I/O usage)

More just out of curiosity, I’ve noticed that every time node is restarted it’s “really busy” as in high I/O usage on HDD (mostly reads) and I can hear the HDD “clicking” away. This typically lasts ~4 hours at this point in time, and then it “calms” down. Obviously, I know that part of it is the interaction with the network traffic. Anyone know what the program is actually doing though, after the node is started up?

I think its going through and loading the database and checking the files. That’s a lot of files to check when it starts to fill up. Oh, also maybe does the garbage collection at that point too.

Is there a limit on the node to optimal drive size for best node performance vs. say 100’s of Terabytes on a single node.

there is, they say somwhere at the beginig 22 or 24 TB is max on 1 node

There is no upper limit. Just estimator have it. Currently having more than a 24TB in one place doesn’t makes any sense - it will not be filled in the foreseeable future anyway.
It could be changed, when the platform becomes very popular.