On 15 Nov 2024, at 22:59, Stephen Morris <steve.morris.au@gmail.com> wrote:

(the hard disk light is permanently on, not flickering) 

There are better tools for investigating this type of I/O issue.

You could have a read of this article that explains how to track down disk I/O
issues: https://www.baeldung.com/linux/monitor-disk-io

If you are interested in systems performance have a look at getting
Brendan Gregg's "Systems Performance" book.

Barry