On Tue, 2005-03-29 at 13:29 +0200, Peter T. Breuer wrote: > Neil Brown <neilb@xxxxxxxxxxxxxxx> wrote: > > Due to the system crash the data on hdb is completely ignored. Data > > Neil - can you explain the algorithm that stamps the superblocks with > an event count, once and for all? (until further amendment :-). I think the best explanation is this: any change in array state that would necessitate kicking a drive out of the array if it didn't also make this change in state with the rest of the drives in the array results in an increment to the event counter and a flush of the superblocks. For example, a transition of a raid array from ro to rw mode results in an event update and a flush of superblocks. If the system then goes down and one drive has the superblock update and another doesn't, then you know that one was behind the other and to kick it. > It goes without saying that sb's are not stamped at every write, and the > event count is not incremented at every write, so when and when? Transition from ro -> rw or from rw -> ro, transition from clean to dirty or dirty to clean, any change in the distribution of disks in the superblock (aka, change in number of working disks, active disks, spare disks, failed disks, etc.), or any ordering updates of disk devices in the rdisk array (for example, when a spare is done being rebuilt to replace a failed device, it gets moved from it's current position in the array to the position it was just rebuilt to replace as part of the final transition from being rebuilt to being an active, live component in the array). -- Doug Ledford <dledford@xxxxxxxxxx> http://people.redhat.com/dledford - 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
