If you have corruption in RAID 1 how do you know which copy is good? On a slight tangent ZFS will checksum data and store that checksum in the block pointer (i

If you have corruption in RAID 1 how do you know which copy is good? On a slight tangent ZFS will checksum data and store that checksum in the block pointer (i.e. not with the data itself) so it can tell which of the copies is correct. The same extends to RAID 5 and RAID 6, although with RAID 6 you can intelligently work out which block might be bad. However that is assuming the block devices are returning consistent data and you are the one talking to the block devices. If the disks were sat behind a hardware RAID controller and the controller was the one you'd be hard pressed to identify the source of the data corruption. The checksumming in ZFS comes to the rescue here again. I recommend checking out this video [1] from Bryan Cantrill. It's about Joyent's object store Manta but features a fair bit of ZFS history. Also it features the usual rant level that one can come to expect from a Bryan Cantrill talk which I quite enjoy. There are plenty of other videos available on ZFS. [1] https://www.youtube.com/watch?v=79fvDDPaIoY https://www.youtube.com/watch?v=79fvDDPaIoY