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Forum Discussion
Ready NAS 100 Resync after power outage
Hi all, I am a new owner of a ready nas 100-4 so I'm not really expert on this platform as so far I always owned and worked with different hardware than this. I installed my disks (3x3TB WD-R...
Hi StephenB,
I agree regarding the file integrity check. After an unexpected shut down you might have corruption on files. The fileystem itself can actually have issues, needs to apply the journals and so on.
What I don't undertand is the whole resync thing: It doesn't make sense to me that the machine, which sees the raid in healty status, start resyncing it. Also, I have no clue about what's actually resyncing and from WHERE!
If you break an HD and you replace it, the resync process takes data from the others to that new hard disk. But in this case I have no idea what's going on and why. The filesystem is still intact though, so it's not recreating the array from scrach but just syncing.. which I can't properly understand what does it means at this point!
Every time you write to the volume, you not only write the data, but you also need to update the corresponding RAID parity blocks. Both of these need to be done as an atomic operation.
If there is a possibility that writes were lost, then of course it is also possible that the parity blocks are out of sync with the data (e.g, the data write completed, but the system went down before the new parity block was written). If that happens, then later on (when a disk is replaced), data corruption will occur, since the parity blocks are used to recreate the data on the new disk.
You deal with this possibility by checking the parity blocks and repairing them. With mdadm, this is generally done with checkarray (and after the file system check), but checkarray is indistinguishable from resync to the kernel.
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