So? Do you think filesystem metadata is stored in a magical pixie cloud, or on the same unreliable physical hardware where it can easily get corrupted, especially after a crash or an unexpected power loss?

I posted this link here already:

https://www.usenix.org/conference/atc19/presentation/jaffer

f2fs (at least in its state a couple of years ago) is/was a prime example of how a filesystem can get into a barely working state with massive amounts of data and metadata corruption, and not even notice it.

God I love this site. In case of a minor disagreement with someone don't even bother to think, just press "downvote".

Corrupt data should be corrected by checksummed btrfs, isn't it?

Only if you have more than one copy of the data

RAID 5 has been generally advised against for years, due to performance issues and the effect of unrecoverable errors during rebuilds.

Btrfs RAID1 works perfectly, and RAID1c3/RAID1c4 provides additional redundancy. In place of RAID5, use RAID10 instead.

raidz2 is only advised against if your arrays are so small that you don't care about the price of storage.

If you want more IOPS, add more raidz2 (raid6) stripes to the pool. In practice, spinning rust is the new tape. Trying to do random access under 1MB is just silly

I don't stress over rebuilds. 2 more disks failing during a rebuild is incredibly unlikely compared to everything else that might force me to restore a backup (software bugs, data center flooding, etc).