Signed-off-by: Song Liu <songliubraving@xxxxxx> Signed-off-by: Shaohua Li <shli@xxxxxx> --- md.4 | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/md.4 b/md.4 index e955c3b..f1b88ee 100644 --- a/md.4 +++ b/md.4 @@ -874,6 +874,26 @@ The list is particularly useful when recovering to a spare. If a few blocks cannot be read from the other devices, the bulk of the recovery can complete and those few bad blocks will be recorded in the bad block list. +.SS RAID456 WRITE JOURNAL + +Due to non-atomicity nature of RAID write operations, interruption of +write operations (system crash, etc.) to RAID456 array can lead to +inconsistent parity and data loss (so called RAID-5 write hole). + +To plug the write hole, from Linux 4.4 (to be confirmed), +.I md +supports write ahead journal for RAID456. When the array is created, +an additional journal device can be added to the array through +.IR write-journal +option. The RAID write journal works similar to file system journals. +Before writing to the data disks, md persists data AND parity of the +stripe to the journal device. After crashes, md searches the journal +device for incomplete write operations, and replay them to the data +disks. + +When the journal device fails, the RAID array is forced to run in +read-only mode. + .SS WRITE-BEHIND From Linux 2.6.14, -- 2.4.6 -- 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
