Cache writes on a RAID to SSD and only do one daily commit to HDD
You could easily do that with a Cronjob on Rsync or something of that effect. RDiff-Backups if your looking for a full blown backup solution.
Here what I would do...
- Backup on the SSD
- Nightly Rsync/RDiff/etc to the HDDs
- HDDs will spins down as you expected and shouldn't be more than idling.
- If your not using the HDDs other than to store data you could even rig up a script to mount and unmount them entirely during these times. If not when you need Samaba to "activate" them. Cutting power usages entirely except during absolute usages as such.