4 ms·

How do you detect bit flips with software RAID? A scrub can detect differences, but without checksums it's ambiguous which copy is wrong. And in the case of mda

by cmurf 11y ago

How do you detect bit flips with software RAID? A scrub can detect differences, but without checksums it's ambiguous which copy is wrong. And in the case of mdadm, which has no concept of a file system, it won't report the affected file. I'm not even sure you get an LBA, but if you do, then you have to go look that up, accounting for offsets, with the chosen file system to get a file. Conversely, Btrfs scrubs will report a corrupt file path if there's a bit flip in a single copy. If there's another copy available then there's just a kernel note that there was a data csum error and the problem was fixed, no file name path.

pslam 11y ago
The entire point of my system is that I don't need to care which copy is good. If it scrubs and detects any error, I'll mount disks independently as two filesystems, and diff the contents. I'll then restore corrupted data from backup. Yes, a checksumming filesystem would be better, but at the time of creation (and even now?) none of the filesystem choices were mature, or proven to be sufficiently reliable. Ext4 and software RAID1 are both mature and proven reliable.