Is it valid to set <max_concurrent> for each of the OpenIFS apps to 0 (I can set it to 1 and try again once the hadam4 has completed)? The official manual doesn't say.

I was using the UUID of the underlying hardware, when I should have been using the UUID of the formatted partition.

I think the problem is that CPDN is treating 2 hosts, as a single host.
eg: L-7113-1 and L-7113-2 are two different hosts. But CPDN see's just 1 host. If I swap out the hard drive, all CPDN does is change the hostname of this device, rather than see it as a seperate device (host).

The link you give is just to show ONLY in progress tasks, this link shows all tasks for that host: https://www.cpdn.org/results.php?hostid=1535374
There is a server setting that doesn't allow multiple clients. The way you have your 2 drives setup means BOINC sees them as the same so when you swap them over the tasks will get abandoned as shown in your full list.

This should work - it's equivalent to running two clients on the same machine, and just shutting one down whilst the 2nd drive is in the machine. It's perfectly possible to run 2 clients on the same host for CPDN (I do it), but there must be two separate client ids. CPDN's server does not see the mac address, only your external (router) IP.

To swap out the disks you'd need to have created a new client instance on the 2nd disk, whilst keeping the original client on the first disk without detaching from the project. That way, CPDN's server will see two client, one for each disk and that should work. If each disk's boinc client datadir has the same client id (check the 'client_state.xml' file) then I suspect you'll get the behaviour you describe.

Dave, Richard, et al..

Can I ask, where have these completed tasks gone?

https://www.cpdn.org/results.php?hostid=1535374&offset=0&show_names=0&state=1&appid=

It says In-Progress but most (if not all) of these have already been completed, uploaded, and reported?

eg I just uploaded and reported one task just a few minutes ago which I downloaded 15 hours ago, but there is nothing showing in the list, just 'in-progress'.

I think the problem is that CPDN is treating 2 hosts, as a single host.

eg: L-7113-1 and L-7113-2 are two different hosts. But CPDN see's just 1 host. If I swap out the hard drive, all CPDN does is change the hostname of this device, rather than see it as a seperate device (host).

The two disks are completely separate. Both have a full install of Ubuntu and BOINC. Only one drive is inserted into the server at any one time.

I have ran this server on many BOINC projects, at different times with each drive, and all projects (except CPDN) see it as 2 different hosts.

At the moment, with the new hardware present but not active, the machine looks like this:
<snipped>
Now I look at it, that needs some work, but I need to get a clearer understanding of what belongs to what. I can't find the label 'hdd' anywhere, and I have no idea where 'File system' lives - but it's got lots of bytes in/on it.

Slot 14, so yes.

Ok, just ls through all slots until I found CPDN.
There's one srf* file in the slot.

sudo ls -l ?/ | grep srf

Reporting certainly, whether it was actually checkpointing as it should if it was supposed to I don't know.

How often? If it's once per second, it's a false report. Real checkpoints happen every few minutes.