January 20, 20251 yr Hey, this might sound like a silly question but it isn't something I can find an definitive answer to online. So I know that Unraid is pretty much just JBOD with parity, but what I would like to know specifically is if any of my non parity drives fail, can all the data on that drive be recovered? So, lets say I have an 8tb, and two 16tb drives with one 16tb as a parity, and either the 8tb or the 16tb (non parity) drives fail. Will any of the data on that failed drive be lost or can the parity drive somehow recover all the lost data?
January 20, 20251 yr Community Expert The data for a missing drive can be recovered by reading parity plus all the other drives and getting the data from the parity calculation. https://docs.unraid.net/unraid-os/overview/nas/#parity-protected-array Parity is basically the same concept wherever it is used on any system. Parity is just an extra bit that allows a missing bit to be calculated from all the other bits. To accurately rebuild all the bits of a missing disk, it must be able to accurately read all the bits of all the other disks.
January 20, 20251 yr Community Expert In simplistic terms as long as the number of failed rives is not more than the number of parity drives then they can be rebuilt. If the number of failed drives exceeds the number of parity drives then the data on the failed drives is lost but the data on the 'good' drives is still there (unlike more traditional RAID systems). You should still have a backup strategy in place for important files as you can still lose files by other means (e.g file system corruption, bad RAM, user error) other than drive failure.
January 20, 20251 yr Community Expert 1 hour ago, itimpi said: If the number of failed drives exceeds the number of parity drives then the data on the failed drives is lost but the data on the 'good' drives is still there (unlike more traditional RAID systems). And it is worth noting that often data can be recovered from the "failed" drives using other methods. Sometimes a drive is "kicked out" of the array for reasons other than a disk actually being bad. Bad connections are much more common than bad disks, for example. Please ask on the forum if you are unsure of how to proceed in the event of any problems.
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