When this last step occurs, because the drive has all zeroes, it does not alter the parity values that were previously calculated, as adding zero to a value does not change a value.ĭuring this drive clearing process, the Unraid system is in a reduced state of performance (Note: it might actually be that Unraid makes the array unusable during the drive zeroing - I've seen that mentioned, but it has been so long since I've allowed Unraid to clear a disk that I truly don't remember). Instead, it first "Clears" the drive by writing zeros to the entire drive, then writes an Unraid signature to the drive, then finally adds the drive to the available storage. When you first add a drive, Unraid does not make it immediately available for use. Unraid also has a great feature in that you can add additional drives at any time, expanding your storage. With dual parity, a different calculation is performed and written to the 2nd parity disk, so that two drives can be rebuilt at the same time. If a drive is replaced, that simple math formula can be reversed to rebuild the contents on the replaced drive. Unraid uses an unusual parity scheme: All the bits from the same position across all drives are added up to calculate a parity value, and that value is written to the same position on the parity disk.
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