Developers behind the Distributed Replicated Block Device "DRBD" for mirroring block devices between multiple host systems are working to resync the upstream Linux kernel DRBD support with the out-of-tree DRBD code they have been maintaining for the past ~15 years out-of-sync. It's a big undertaking but they have begun staging patches for review and testing to get this massive set of changes up to par for mainline.

DRBD was accepted to the mainline kernel back in 2009 but for well over a decade hasn't been maintained too well while the out-of-tree code has continued to progress for mirroring block storage devices between hosts. During this time DRBD out-of-tree has continued to be maintained by the commercial company LINBIT focused on enterprise software-defined storage. Engineers at LINBIT are now working to reduce that delta against the upstream kernel code.