On 12 Feb 2019, Robin Hill uttered the following: > From what I recall of the details, unlike other RAID levels, RAID1 > doesn't bother taking a copy of the buffer to be written (as it's going > to write the same data to all drives anyway), which means the data can > be changed between writes to the different disks. The mismatch only > happens if there's no further write command issued after the change > (otherwise the changed data would get rewritten to all disks), which > means the data written won't be re-used. This is most common with swap, > but can happen with other applications which write temporary data to > disk. Hm. So writable mmap(), bang on it, then don't issue an msync(), and you might if you're unlucky get the old data written to one disk and the new data to the other one? As long as msync() resolves this that seems OK: POSIX explicitly does not guarantee that changes get written back without an msync(), after all. -- NULL && (void)
