The big issue we want to prevent is that multiple drives start to develop bad sectors at the same time, because that is the equivalent of multiple simultaneous drive failures, which many RAID arrays can't recover from.įor home users I would recommend checking all hard drives once a month. For a RAID array, it's just equivalent to a failed drive and an affected drive will be kicked out of the RAID array if bad sectors start causing read errors. RAID solutions are perfectly capable of handling bad sectors. If you bought a NAS from QNAP, Synology or another vendor, there is a menu which allows you to control how often and when you want to perform a data scrub. Yes: all the sectors.Ĭhecking your hard drives for bad sectors (or other issues) is called 'data scrubbing'. The only way to find out if a disk has developed bad sectors is to just read them all. The mitigation: periodic scrubbing / checking of your disks If you run a (variant of) RAID 5, you can only lose a single disk, so if a second disk fails, you lose all data 5. Due to the bad sectors, data required to rebuild the array is lost because there is no longer any redundancy 4. That means effectively a second drive has failed although the drive may still seem operational. In this scenario, a hard drive in their RAID array has failed and a second drive (one of the remaining good drives) has developed bad sectors. Your data might be at risk right at this moment while you are reading this article.Ī well-known disaster scenario in which people tend to lose data is double hard drive failure where only one drive faillure can be tolerated (RAID 1 (mirror) or RAID 5, and in some scenario's RAID 10). One or more of your hard drives may be developing bad sectors and you wouldn't even know it. Most of that data is probably not frequently accessed, especially at home. With todays 14+ TB hard drives, it's easy to store vast amounts of data. This is the thing: those bad sectors may never be discovered until it is too late! How small a sector may be, if any data is stored in them, it is now lost and this could cause data corruption (one or more corrupt files). Bad sectors are tiny portions of the drive that have become unreadable 3. The problem is that hard drives may develop bad sectors over time. But still, it would be nice if we would reduce the risk of dataloss to a minimum. They may decide to take the risk and only backup a small portion of the really important data and take their chances with the rest. Since backup storage costs money, people make tradeoffs. So ideally, even if the NAS would go up in flames, you would still have your data. Obviously, the best way to protect against dataloss, is to make regular backups. Maybe it's a COTS device from one of the well-known vendors 1, or it's a custom build solution (DIY 2) based on hardware you bought and assembled yourself.īuying or building a NAS is one thing, but operating it in a way that assures that you won't lose data is something else.
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