An out-of-sync RAID leg results from a device failure. If it's temporary and the device recurs, run "lvchange --refresh $RaidLV" to cause it to be resynchronized. Once that's finished, run "lvconvert -m0 $RaidLV" again to downgrade the raid1 to linear. Commit d7e922480e04ecfb7c4d8b2d42533699ddef5c34