I just happened to find that parameter mentioned in some ZFS root setup guides and tried it as a wild guess.
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to zfs-linux in Ubuntu. https://bugs.launchpad.net/bugs/1673197 Title: Upgrading zfs-initramfs breaks booting from a zfs root Status in zfs-linux package in Ubuntu: In Progress Bug description: Upgrading to zfs-initramfs 0.6.5.9-4ubuntu1 breaks my boot. I've EFI and a small ext2 boot partition, and the rest of my SDD is a zfs pool. After upgrade I'm dropped in the initramfs shell and no zpools are available. Downgrading to 0.6.5.8-0ubuntu9 makes it boot again. ProblemType: Bug DistroRelease: Ubuntu 17.04 Package: zfs-initramfs 0.6.5.9-4ubuntu1 ProcVersionSignature: Ubuntu 4.10.0-11.13-generic 4.10.1 Uname: Linux 4.10.0-11-generic x86_64 NonfreeKernelModules: zfs zunicode zavl zcommon znvpair ApportVersion: 2.20.4-0ubuntu2 Architecture: amd64 CurrentDesktop: Unity:Unity7 Date: Wed Mar 15 18:29:04 2017 InstallationDate: Installed on 2016-05-06 (312 days ago) InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1) PackageArchitecture: all SourcePackage: zfs-linux UpgradeStatus: Upgraded to zesty on 2016-11-22 (113 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/zfs-linux/+bug/1673197/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : email@example.com Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp