Do you have plans to look at whether higher fluctuations translate into higher failure rates? Not sure whether you have historical data on this, but I would be really interested in this aspect, even if you can only run the stats on a smaller number of drives or shorter time periods.
Maybe dividing the drives roughly in "higher than average variability" and "low variability" and then looking at the AFR for this subset can show some relation. Of course as the AFR for many drives is already quite low, the effect might be too small to distinguish from noise.
On the topic of temperatures: Have you run an analysis whether a drive increasing in temperature (or maybe even decreasing) compared to its base line and "neighbors" results in a higher chance of failure?
Maybe dividing the drives roughly in "higher than average variability" and "low variability" and then looking at the AFR for this subset can show some relation. Of course as the AFR for many drives is already quite low, the effect might be too small to distinguish from noise.
On the topic of temperatures: Have you run an analysis whether a drive increasing in temperature (or maybe even decreasing) compared to its base line and "neighbors" results in a higher chance of failure?