mdadm: Add description of write journal to md.4
Signed-off-by: Song Liu <songliubraving@fb.com> Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: NeilBrown <neilb@suse.com>
This commit is contained in:
parent
051f326550
commit
28f83f6d3b
20
md.4
20
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
|
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.
|
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
|
.SS WRITE-BEHIND
|
||||||
|
|
||||||
From Linux 2.6.14,
|
From Linux 2.6.14,
|
||||||
|
|
Loading…
Reference in New Issue