= eoan verification =
ubuntu@ip-172-30-0-147:~$ sudo mdadm --create /dev/md0 --run --metadata=default
--level=0 --raid-devices=2 /dev/xvdb /dev/xvdc
mdadm: Fail create md0 when using /sys/module/md_mod/parameters/new_array
mdadm: array /dev/md0 started.
ubuntu@ip-172-30-0-147:~$ cat /proc/mdstat
Personalities : [raid0]
md0 : active raid0 xvdc[1] xvdb[0]
3141632 blocks super 1.2 512k chunks
unused devices: <none>
# Upgraded mdadm & installed a 5.4 kernel
ubuntu@ip-172-30-0-147:~$ dmesg | grep raid
[ 3.009968] md: If you don't use raid, use raid=noautodetect
[ 5.981265] md/raid0:md0: cannot assemble multi-zone RAID0 with
default_layout setting
[ 5.993787] md/raid0: please set raid0.default_layout to 1 or 2
ubuntu@ip-172-30-0-147:~$ sudo mdadm --stop /dev/md0
mdadm: stopped /dev/md0
ubuntu@ip-172-30-0-147:~$ sudo mdadm --assemble -U layout-alternate /dev/md0
/dev/xvdb /dev/xvdc
mdadm: /dev/md0 has been started with 2 drives.
ubuntu@ip-172-30-0-147:~$ cat /proc/mdstat
Personalities : [raid0]
md0 : active raid0 xvdb[0] xvdc[1]
3141632 blocks super 1.2 512k chunks
unused devices: <none>
## reboot
ubuntu@ip-172-30-0-147:~$ dmesg | grep raid
[ 2.440539] md: If you don't use raid, use raid=noautodetect
ubuntu@ip-172-30-0-147:~$ cat /proc/mdstat
Personalities : [raid0]
md0 : active raid0 xvdb[0] xvdc[1]
3141632 blocks super 1.2 512k chunks
unused devices: <none>
ubuntu@ip-172-30-0-147:~$ sudo mdadm --stop /dev/md0
mdadm: stopped /dev/md0
ubuntu@ip-172-30-0-147:~$ sudo mdadm --create /dev/md0 --run --metadata=default
--level=0 --raid-devices=2 /dev/xvdc /dev/xvdb
mdadm: /dev/xvdc appears to be part of a raid array:
level=raid0 devices=2 ctime=Fri Dec 6 21:30:03 2019
mdadm: /dev/xvdb appears to be part of a raid array:
level=raid0 devices=2 ctime=Fri Dec 6 21:30:03 2019
mdadm: array /dev/md0 started.
ubuntu@ip-172-30-0-147:~$ sudo mdadm --stop /dev/md0
mdadm: stopped /dev/md0
ubuntu@ip-172-30-0-147:~$ sudo mdadm --create /dev/md0 --run --metadata=default
--level=0 --raid-devices=2 /dev/xvdc /dev/xvdb --layout=original
mdadm: /dev/xvdc appears to be part of a raid array:
level=raid0 devices=2 ctime=Fri Dec 6 21:52:42 2019
mdadm: /dev/xvdb appears to be part of a raid array:
level=raid0 devices=2 ctime=Fri Dec 6 21:52:42 2019
mdadm: array /dev/md0 started.
ubuntu@ip-172-30-0-147:~$ sudo mdadm --detail /dev/md0 | grep Layout
Layout : original
** Description changed:
Bug 1849682 tracks the temporarily revert of the fix for this issue,
while this bug tracks the re-application of that fix once we have a full
solution.
[Impact]
(cut & paste from https://marc.info/?l=linux-raid&m=157360088014027&w=2)
An unintentional RAID0 layout change was introduced in the v3.14 kernel. This
effectively means there are 2 different layouts Linux will use to write data to
RAID0 arrays in the wild - the “pre-3.14” way and the “3.14 and later” way.
Mixing these layouts by writing to an array while booted on these different
kernel versions can lead to corruption.
Note that this only impacts RAID0 arrays that include devices of
different sizes. If your devices are all the same size, both layouts are
equivalent, and your array is not at risk of corruption due to this
issue.
Unfortunately, the kernel cannot detect which layout was used for writes
to pre-existing arrays, and therefore requires input from the
administrator. This input can be provided via the kernel command line
with the raid0.default_layout=<N> parameter, or by setting the
default_layout module parameter when loading the raid0 module. With a
new enough version of mdadm (>= 4.2, or equivalent distro backports),
you can set the layout version when assembling a stopped array. For
example:
mdadm --stop /dev/md0
mdadm --assemble -U layout-alternate /dev/md0 /dev/sda1 /dev/sda2
See the mdadm manpage for more details. Once set in this manner, the layout
will be recorded in the array and will not need to be explicitly specified in
the future.
(The mdadm part of this SRU is for the above support ^)
[Test Case]
= mdadm =
Confirm that a multi-zone raid0 created w/ older mdadm is able to be started
on a fixed kernel by setting a layout.
1) Ex: w/ old kernel/mdadm:
- mdadm --create /dev/md0 --run --metadata=default \
- --level=0 --raid-devices=2 /dev/vdb1 /dev/vdc1
+ mdadm --create /dev/md0 --run --metadata=default \
+ --level=0 --raid-devices=2 /dev/vdb1 /dev/vdc1
2) Reboot onto fixed kernel & update mdadm
- 3) sudo mdadm --assemble -U layout-alternate \
- /dev/md0 /dev/vdb1 /dev/vdc1
+ 3) sudo mdadm --stop /dev/md0 &&
+ sudo mdadm --assemble -U layout-alternate \
+ /dev/md0 /dev/vdb1 /dev/vdc1
4) Confirm that the array autostarts on reboot
5) Confirm that w/ new kernel & new mdadm, a user can create and start an
array in a backwards-compatible fashion (i.e. w/o an explicit layout).
- 6) Verify that 'mdadm --detail /dev/md0' displays the layout
+ 6) Verify that 'mdadm --detail /dev/md0' displays the layout
= linux =
Similar to above, but using kernel command line options.
[Regression Risk]
The kernel side of things will break starting pre-existing arrays. That's
intentional.
Although I've done due-diligence to check for backwards compatibility
issues, the mdadm side may still present some.
** Tags removed: verification-needed-eoan
** Tags added: verification-done-eoan
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https://bugs.launchpad.net/bugs/1850540
Title:
multi-zone raid0 corruption
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