** Changed in: linux (Ubuntu Bionic)
Status: Confirmed => Fix Committed
** Changed in: linux (Ubuntu Disco)
Status: Confirmed => Fix Committed
** Changed in: linux (Ubuntu Eoan)
Status: Confirmed => Fix Committed
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https://bugs.launchpad.net/bugs/1850540
Title:
multi-zone raid0 corruption
Status in Release Notes for Ubuntu:
New
Status in linux package in Ubuntu:
Confirmed
Status in mdadm package in Ubuntu:
Fix Released
Status in linux source package in Precise:
New
Status in mdadm source package in Precise:
New
Status in linux source package in Trusty:
Confirmed
Status in mdadm source package in Trusty:
Confirmed
Status in linux source package in Xenial:
Confirmed
Status in mdadm source package in Xenial:
Confirmed
Status in linux source package in Bionic:
Fix Committed
Status in mdadm source package in Bionic:
Fix Committed
Status in linux source package in Disco:
Fix Committed
Status in mdadm source package in Disco:
Fix Committed
Status in linux source package in Eoan:
Fix Committed
Status in mdadm source package in Eoan:
Fix Committed
Status in linux source package in Focal:
Confirmed
Status in mdadm source package in Focal:
Fix Released
Status in mdadm package in Debian:
Fix Released
Bug description:
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
2) Reboot onto fixed kernel & update mdadm
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
= 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.
The mdadm side will cause a regression in functionality where a user
can no longer create multi-zone raid0s on kernels that do not yet have
the raid0 layout patches. This is intentional, as such RAID arrays
present a corruption risk.
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