Main concerns:
- Loss of data logging facility.
- Loss of historic data.
- Partition each SD Card with the OS on one partition and the software and results on the other. Mark the OS partition Read-only so that and SD Card failure does not prevent the Pi operating. However, the results and logs on the other partition could be lost; shouldn't be a problem assuming that the NAS is still working.
- Just use the built-in RAID feature.
- I need to find a way of notifying us when a drive fails - otherwise this isn't very useful.
- Run a script/similar on the NAS box regularly to backup to USB storage.
- Still store results in files, but do it to separate USB storage independent of the NAS box.
- Use USB storage attached to 1 or more of the Pis for storing backup readings.
- Awkward price-wise, cos only 1 USB port on the Pis.
- Using the WAL (Write-Ahead Log) to stream to a fallover database.
- Good idea, but potentially complicated.
- Also requires the NAS box database to support this, but it might not cos it's old and I haven't been able to cross-compile a newer database system.
- Would also require another database server (?).
- Would allow the system to continue running normally if the NAS box goes down?
I've never even heard of this before, so I'll need to look into it and get back to you.
We need to be careful here - there's definitely the potential for making things over-complicated and for feature-creep. Having said that, there's ample time to sort this out, especially seeing as I have the NAS box with me for the foreseeable future. It's also much easier to get all of this stuff in place now, rather than when the NAS box is installed at WMT.
Hamish