I've checked the error logs and they don't look good for the time just before it all stopped working - there are a lot like this:
.convert.bin: Corrupt JPEG data: premature end of data segment `/opt/bitnami/apps/resourcespace/htdocs/filestore//4/8/9_5dde16be6b7ae60/489_4b5b63174e5f908.jpg' @ warning/jpeg.c/JPEGWarningHandler/343.
The filestore folder still has folders/files in it. I downloaded all these and there was ~4.5gb of images (I'd have expected more, maybe twice that size).
The images that are there still open OK, but I'm guessing something bad happened - the other half of the error log has a number of these errors:
[Tue Apr 19 05:30:46.219587 2016] [pagespeed:error] [pid 13144] [mod_pagespeed 184.108.40.206- @13144] /opt/bitnami/apache2/var/cache/mod_pagespeed/http,3A/,2Frs.psc.org.nz/lib/OpenLayers/OpenLayers.js,d8HSo1:1589: writing file: No space left on device
So would I be right in thinking the server ran out of space and caused some corruption in the database/filestore which has caused this to happen?
All isn't lost, I suppose, since I still have a lot of the images and can reupload them. I've tried uploading a new resource (after resizing the server) and it uploads/displays fine.
Another question - there was no warning that the server was getting full; is there usually a notification, or is it more possible that the client batch uploaded gigabytes of files and the server didn't get a chance to notify?
Thanks again David, I think it's nearly as resurrected as it can possibly be. Your help has been extraordinarily valuable.