Phillip Susi <psusi <at> cfl.rr.com> writes: > when mdadm > --incremental sees the second disk claims the first disk is failed, but > it is active and working fine in the running array, it should realize > that the superblock on the second disk is wrong, and correct it, which > would leave the second disk as failed, removed, and neither use the out > of sync data on the disk, nor overwrite it with a copy from the first. "Correcting the superblocks" of conflicting members, would translate into having a defined way to mark those members as composing a segment that contains a known alternative version of the array. The earliest an alternative version can be detected, and thus be known and marked as such, is on an incident when a conflicting segment comes up while another segment of the array is already running degraded. (To simply support segments consisting of single raid member devices it may be enough if a superblock marking itself as failed would mean it is contains conflicting changes. Multi member segments would require segment IDs) IMHO all segments with alternative versions can be marked as known on such incidences. However whether the segments containing alternative versions continue to be normally assembled when they come up after the incident like before, or if they get ignored in favor of the arbitrary first segment of the incidence, should be configurable. For users that don't need or want to be able to switch between versions of an array by simply switching disks in a hot-pluggable manner, and for those concerned about a failure mode that may exist and make disks available in an alternating manner and them not noticing it all the time until an incident, I suggested "AUTO -SINGLE_SEGMENTS_WITH_KNOWN_ALTERNATIVE_VERSIONS". In order to manage segments with alternative versions in a hot-plug manner however, all segments need to continue to show up under their real array ID, if they are connected first or one at a time. (KNOWN_ALTERNATIVE_VERSIONS need to be assembled if they come up.) If the segments would be transformed into separate arrays the system won't recognize the segment of the array as such and not boot or open it correctly any more. And you wouldn't be able to switch between versions by switching the disks that are connected. Kind regards, Christian -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
