[DRBD-user] drbd-9.1.7-rc.2

[Philipp Reisner]

Hello,

You all noticed the unusual long rc.1 phase. We were working on smaller
issues with unfreezing IO-requests after quorum loss and regaining
quorum. At this point, one thing gave the other. We discovered how difficult
it is to gracefully recover a primary node that lost quorum. It was like a
super narrow path, where every misstep led to the need to reboot the
node. Examples:
  * When you did a drbdadm secondary while someone held the device open (a
    mounted FS) -> deadlock [fixed now].
  * You needed to reconfigure 'on-no-quorum' from 'suspend' to 'io-error' and
    then unmount the filesystem
  * Finally, make the node secondary and re-integrate it with the others

Changing the DRBD configuration just for recovering a node is not
practicable when we advertise to use LINSTOR for configuring DRBD. The
end-users are even not aware of LINSTOR but use it through the Kubernetes
and the linstor CSI driver.

The solution: drbdadm secondary --force
Starting with the next drbd-utils v9.21 a forced demotion allows you to make
a primary with suspended IOs secondary. All the frozen IO requests terminate
with IO-errors, causing the filesystem to go into read-only mode. Unmount
it. Recovery finished.
For a similar purpose, it got a new configuration option
'on-suspended-primary-outdated' which you can set to 'force-secondary'. This
enables automatic recovery of such a primary lost quorum IO suspended
node. When it connects to a partition that has a primary with a more recent
data generation it automatically demotes the primary with the older data and
frozen IO.

It also got compatibility for up to Linux 5.15 (hello Ubuntu users, your
next LTS will land in about 2 weeks and have such a kernel).

PS: Looks like on this 5.15 kernel there is a new way to deadlock DRBD with
IO errors from the lower layers. (we are investigating right now)

Please help test these new features, and everything else.

9.1.7-rc.2 (api:genl2/proto:110-121/transport:17)
--------
 * avoid deadlock upon trying to down an io-frozen DRBD device that
   has a file system mounted
 * fix DRBD to not send too large resync requests at multiples of 8TiB
 * fix for a "forgotten" resync after IO was suspended due to lack of quorum
 * refactored IO suspend/resume fixing several bugs; the worst one could
   lead to premature request completion
 * disable discards on diskless if diskful peers do not support it
 * make demote to secondary a two-phase state transition; that guarantees that
   after demotion, DRBD will not write to any meta-data in the cluster
 * enable "--force primary" in for no-quorum situations
 * allow graceful recovery of primary lacking quorum and therefore
   have forzen IO requests; that includes "--force secondary"
 * following upstream changes to DRBD up to Linux 5.15 and updated compat

https://pkg.linbit.com//downloads/drbd/9/drbd-9.1.7-rc.2.tar.gz
https://github.com/LINBIT/drbd/commit/7434965d91d0e275dacc2940177a28eed5a17f4d