Am 13.02.19 um 18:44 schrieb Robert L Mathews: > This seems correct. I once closely examined mismatched blocks on a RAID > 1 array on one of our mail servers, and found that they were one byte > differences caused by Postfix doing this: > > 1) writing a queue file with the "has been delivered to recipient X" > byte set to 0; > > 2) issuing a write that would change that byte to 1; > > 3) deleting the file. > > Step 2 occasionally gets written to only one of the disks, with the > others ignoring the write because the step 3 deletion happens to occur > before they get around to the step 2 write. But that's harmless; as you > say, it appears to happen only with blocks that by definition are never > going to be re-read. > > You can imagine all sorts of things that do something similar: for > example, you could append a few bytes to the end of a file, then > truncate the file to a smaller size, and it wouldn't matter whether > those bytes ever reached all the disks. > > Because of that, mismatched blocks on a RAID 1 array don't necessarily > seem to be an indicator of a problem. besides that "mismatch_cnt" is pretty useless when you can't distinct harmless versus a real problem.....
