path: root/md.4
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Diffstat (limited to 'md.4')
1 files changed, 20 insertions, 0 deletions
diff --git a/md.4 b/md.4
index e955c3b4..f1b88ee6 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.
+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
+When the journal device fails, the RAID array is forced to run in
+read-only mode.
From Linux 2.6.14,