I have a NAS appliance that is just over a month old. It is configured to email me alerts generated from the hard drives' SMART data. After one day, one of the hard drives reported that a sector had gone bad and been reallocated. Over the first week, that number climbed to six total sectors for the hard drive in question. After a month, the number stands at nine reallocated sectors. The rate definitely seems to be decelerating.
The NAS is configured with six 1.5 TB drives in a RAID-5 configuration. With such high capacity drives, I would expect a sector to fail from time to time, so I was not concerned when the first few sectors were relocated. It bothers me though that none of the other disks are reporting any problems.
At what rate of relocations, or total number of relocations, should I start to get worried for the drive's health? Might this vary based on the capacity of the drive?
Best Answer
Drives, like most components, have a bathtub curve failure rate. They fail a lot in the beginning, have a relatively low failure rate in the middle, and then fail a lot as they reach the end of their life.
Just as the whole drive follows this curve, particular areas of the disk will also follow this curve. You'll see a lot of sector re-allocations in the beginning of using the drive, but this should taper off. When the drive starts to fail at the end of life it'll start losing more and more sectors.
You don't need to worry about 6 (depending on the drive - consult the manufacturer), but you need to watch and see the frequency of each new reallocation. If the deterioration accelerates or stays the same, worry. Otherwise, it should be fine after the initial break-in period.
-Adam