@gridsah
看来是你没有认真理解。

首先发生的是 FS 检查，所以不会落入你说的问题中。
（实际上你说的问题，是常见的误区，即 RAID1/5 的问题，当冗余不一致时，根本无从判断哪个正确。）

但是当 DSM 开启数据检验时，它可以根据 CRC 确定哪个副本是正确的。

CRC32-C Checksums - Checksums will be generated for user data and metadata to avoid silent corruption. If a checksum mismatch is detected during a reading process, it will first try to recover automatically, by obtaining a good copy of this block for metadata. If no good copy is available, an error will be reported to the user.
• Silent data corruption detection and recovery (file self-healing) - In DSM 6.1 and above, Btrfs file system has the ability to not only detect the silent corruption on the user data but also to recover it. If checksum mismatch is detected, the file system layer instructs MD layer to read redundant copy (parity or mirror) of the damaged block. It will then automatically recover the damaged block with the good redundant copy. This file self-healing feature requires the RAID volumes to run RAID 1, 5, 6, 10, F1, or SHR.