Summary:
yast partitioner creates raid devices always with "metadata=1.0" and therefore
it's not possible to add a journal to a RAID5 device. Workaround: Create the
RAID5 manually, because then the default metadata version 1.2 is used, which
supports journal.
When I create a new RAID5 with YaST2 partitioner (storage-ng), then the raid
version (metadata) is always 1.0.
In fact it's hard coded in file libstorage-ng-master/storage/Devices/MdImpl.cc:
string cmd_line = MDADM_BIN " --create " + quote(get_name()) + " --run
--level=" +
boost::to_lower_copy(toString(md_level), locale::classic()) + "
--metadata=1.0"
" --homehost=any";
A few years ago mdadm got a new feature to fight the "write hole" of RAID5:
journaling.
see https://www.kernel.org/doc/Documentation/md/raid5-cache.txt
I would like the test it (--add-journal), but it's not working:
# mdadm --detail /dev/md127
/dev/md127:
Version : 1.0
Creation Time : Tue Apr 7 22:39:34 2020
Raid Level : raid5
Array Size : 16776960 (16.00 GiB 17.18 GB)
Used Dev Size : 8388480 (8.00 GiB 8.59 GB)
Raid Devices : 3
...
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
3 8 48 2 active sync /dev/sdd
# mdadm --manage /dev/md127 --readonly --add-journal /dev/sde
mdadm: Failed to hot add /dev/sde as journal, please try restart /dev/md127.
# mdadm --stop /dev/md127
mdadm: stopped /dev/md127
# mdadm --assemble /dev/md127 /dev/sd[bcd]
mdadm: /dev/md127 has been started with 3 drives.
# mdadm --manage /dev/md127 --readonly --add-journal /dev/sde
mdadm: Failed to hot add /dev/sde as journal, please try restart /dev/md127.
------------
However, it works when metadata=1.2 (which is the default for mdadm)
tw2019:/home/dom # mdadm --stop /dev/md127
mdadm: stopped /dev/md127
tw2019:/home/dom # mdadm --create /dev/md127 --level=5 --raid-devices=3
/dev/sd[bcd]
mdadm: /dev/sdb appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Apr 7 22:39:34 2020
mdadm: /dev/sdc appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Apr 7 22:39:34 2020
mdadm: /dev/sdd appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Apr 7 22:39:34 2020
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md127 started.
# mdadm --detail /dev/md127
/dev/md127:
Version : 1.2
Creation Time : Tue Apr 7 22:47:35 2020
Raid Level : raid5
Array Size : 16758784 (15.98 GiB 17.16 GB)
Used Dev Size : 8379392 (7.99 GiB 8.58 GB)
Raid Devices : 3
...
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
3 8 48 2 active sync /dev/sdd
# mdadm --manage /dev/md127 --readonly --add-journal /dev/sde
mdadm: Journal added successfully, making /dev/md127 read-write
mdadm: added /dev/sde
# mdadm --detail /dev/md127
/dev/md127:
Version : 1.2
Creation Time : Tue Apr 7 22:47:35 2020
Raid Level : raid5
Array Size : 16758784 (15.98 GiB 17.16 GB)
Used Dev Size : 8379392 (7.99 GiB 8.58 GB)
Raid Devices : 3
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Tue Apr 7 22:48:48 2020
State : clean
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 512K
Consistency Policy : journal
Name : tw2019:127 (local to host tw2019)
UUID : 5dec6792:8109c604:970842a7:44f0d9e8
Events : 19
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
3 8 48 2 active sync /dev/sdd
4 8 64 - journal /dev/sde
=>
Use the default metadata (1.2) for new RAID devices.
For RAID1 there could be some reasons to stick with version 1.0.
See also :
yast-storage-ng-master/src/lib/y2storage/boot_requirements_strategies/uefi.rb
# EFI in RAID can work, but it is not much reliable.
# See bsc#1081578#c9, FATE#322485, FATE#314829
# - RAID metadata must be somewhere where it will not interfere with
UEFI reading
# the disk. libstorage-ng currently uses "mdadm --metadata=1.0" which
is OK
# - The partition boot flag must be on
# - The partition RAID flag must be on (but setting it resets the boot
flag)