[gruez]

>The modern linux kernel doesn't actually write to disk when fsync is called

Source for this? This seems to be contradicted by the man page for fsync

https://man7.org/linux/man-pages/man2/fdatasync.2.html

       fsync() transfers ("flushes") all modified in-core data of (i.e.,
       modified buffer cache pages for) the file referred to by the file
       descriptor fd to the disk device (or other permanent storage
       device) so that all changed information can be retrieved even if
       the system crashes or is rebooted.  This includes writing through
       or flushing a disk cache if present.  The call blocks until the
       device reports that the transfer has completed.

>I configured the kernel to only write to disk once an hour or when the buffer filled up. That effectively meant I was only writing to disk once per hour when I shut down to change classes.

Sounds great until you get a kernel panic or random shutdown, in which case you potentially get file corruption and/or data loss.