A recent case of filesystem corruption (due to disk trouble) resulted in corrupted files.
My NVX uses XRAID2, and I was expecting parity check on reads to be enabled to detect (and possibly fix) the faulty sectors one of the disks was experiencing. Since parity check was not enabled on the raid, wrong data was relocated basically destroying the etx4 structure.
I am assuming that the faulty data could have been detected on read if the raid controller had support parity check on read...
Now my questions concerning the raid implementation in the NVX are:
1) Is parity check on XRAID2 possible ? => I accept performance penalty on read, data consistency is of higher importance to me
2) Is parity check on NVX possible, and if yes... how do I configure that ?
Disk scrubbing is nice to run through the whole disk, but it would be nice to have some detection of corruption (and possible fix by relocating) while accessng data.
You can only use the parity check to repair if the NVX knows which disk has the corrupt data. If all the sectors can be read, there is no way to tell which one is errored.
When you hot-add a disk, the NAS is rebuilding the disk from the remaining ones - which can be done, since by definition the new disk has no data/corrupt data.
Technically speaking, Raid-5 can repair data erasures (e.g, one sector removed/not readable), but can not do data correction.
In principle RAID-6 could do data correction of one bad sector. It would be a nice capability, maybe Netgear will add it sometime.
