[CentOS] Hard disk activity will not die down

Mon Feb 3 19:28:27 UTC 2020
Chris Pemberton <pchris.bci at gmail.com>

I updated my backup server this weekend from CentOS 7 to CentOS 8.
OS disk is SSD, /dev/md0 are two 4TB WD mechanical drives.
No hardware was changed.

1. wiped all drives
2. installed new copy of 8 on system SSD
3. re-created the 4TB mirror /dev/md0 with the same WD mechanical drives
4. created the largest single partition possible on /dev/md0 and formatted
it ext4
5. waited several hours for the creation of /dev/md0 to finish
6. copied all data back onto /dev/md0

Both installs were a full workstation, with Gnome.
The mirror is mounted via fstab as:
/dev/md0 /mnt/raid1 ext4 defaults 0 0

Under CentOS 7 the /dev/md0 mirror was silent when not in use.  Now under
8, the hard drives are constantly "pinged" by some process, at about the
same frequency as a heartbeat monitor.  I can not figure out what process
is keeping them active.  iotop does show a process named [ext4lazyinput].

Is there something I've missed?