As far as I know it has always shown the temp until I went in there yesterday and noticed it was empty
Yes, disk spindown is enabled on the NAS
I went into Disk 4 shares through the Web UI and I could hear the drive spinning up and now it shows the temp.
Disk 4 is used for backing up XBOX and PS3 games so I rearely access it and it is a good thing that it doesn't spin up with the others and would like to do the same with Disk 1 now
I went into Disk 4 shares through the Web UI and I could hear the drive spinning up and now it shows the temp.
The disks are queried periodically using the smart interface, and the stats are updated using that info. AFAIK the smart specs don't specify whether a spun-down disk needs to respond to that query [or not]. I do know that my own WD disks will sometimes show no temps (and I also have spin-down enabled).
Anyway, I think it's clear that spindown is the cause.
The ReadyNAS OS is on the disks, and there as a RAID-1 mirror of the OS on every disk (including disk 4). So anything that writes to the OS partition (for instance anything that is logged) will result in all disks spinning up eventually. How often that happens depends on the caching strategy in the NAS, and also the caching strategy built into the hard drives.
Reads are another matter, as any spun-up disk will work. But the NAS boots from the first disk it finds (disk 1 in your case), and AFAICT most read requests of the OS partition end up being read from disk 1. So it generally will spin up more often than the others, and there isn't much you can do about that.
