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I have a 2-bay Synology NAS with SHR (synology hybrid RAID) configuration.

I replaced old disks with 2 larger new by making 2 RAID re-sync as described in this article by synology:

  • turned off the nas
  • replaced 1 disk
  • powered on the nas
  • triggered volume repair
  • waited for the synchronization to finish
  • and did the same with the other disk

Now, can I be sure that the current RAID volume is an exact copy of the old disks? Or should I double check it with diff (binary mode) before wiping the old disks?

I mean, does the RAID parity check assure me the copy has been done bit by bit and checked for possible copy errors?

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Does the RAID parity check assure me the copy has been done bit by bit and checked for possible copy errors?

RAID guarantees volume availability, not that the data is correct. Yes, the parity check should reproduce an identical copy of the data. However, nothing is perfect and in rare cases there can be differences. Any time data is written, it is possible for it to be wrong. Bit errors can occur at any point in the system, but it is rare. Depending on how important the data is to you, you might consider a compare of the data to make sure its identical.

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  • Yes, i know they are rare... but unfortunately I've experienced it in the past (problems with a RAM module) so I'm scared of them :) Thanks for the answer, I will check important data and trust the NAS for the rest.
    – Teejay
    Commented Mar 28, 2021 at 12:13
  • @Teejay There is no replacement for proper backups! And testing restoring backups is just as important as making them!
    – Keltari
    Commented Mar 28, 2021 at 14:59

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