To those that use qnap NAS storage there is a known  silent data corruption if you use RAID 5 or RAID 6. If your NAS is NOT  listed in the qnap article below, your NAS is affected!

You will need to install a new firmware update which installs RAID scrubbing and then initialize the actual scrub.

Here is how to do the RAID Scrubbing:

  1. Log on to QTS as administrator.
  2. Go to "Storage Manager" > "Storage Space".
  3. Select the storage pool or volume that contains the RAID 5 or RAID 6 group and then click "Manage".
  4. Select the RAID group, click "Manage", and then select "RAID Scrubbing".

Reddit | QNAP Article | QNAP FAQ