I have a NAS which has been running 24/7 for a little over 3.5 years. So far I've had no drive failures, however I was wondering when I should swap them out with newer drives. Do WD Red drives tend to last a long time?
As stated by DrMoishe Pippik, "There's no point in replacing a drive with good SMART statistics" (plus, un-needed replacement means un-needed heavy workload on the remaining disks to rebuild the array).
Then the choice is between:
- waiting for a disk failure to replace it
- periodically monitoring the SMART reports and replace a disk as soon as a report shows "pre-fail" signs
Drawbacks of 1):
- if another disk is near-failure at that time, it has more chances to fail during the rebuild of the array (heavy workload...)
- you have to replace the disk ASAP, in order to minimize the period during which the array runs without redundancy. During the rebuild, the NAS will have degraded performances
Advantages of 2):
- you can more easily chose the moment for the replacement/rebuild, for instance at night or during the week-end, when the NAS is less solicited
Clearly, 2) is the way to go...
At the very least you should expect to replace them by the end of the warranty period - that's how long the manufacturer believes a fair proportion of them will last.
For a (rather large) real-world data point, see Backblaze's hard drive stats.