Bug#775395: partman-zfs in d-i jessie image does not create grub-compatible /boot ZFS mirror

[Steven Chamberlain <steven@pyro.eu.org>]

tags 775395 + confirmed
user 775395 debian-bsd@lists.debian.org
usertags 775395 + kfreebsd
thanks

Hi Mike,

On 09/02/15 03:02, Michael Milligan wrote:
> This may help...  10.1 added a bunch of feature flags that grub may need
> to now support in the ZFS code and are probably tripping this all up.

You're absolutely right, some of the new feature flags are breaking
GRUB;  I just confirmed it in a fresh test-install with ZFS mounted on /boot

This is my fault;  I was so sure that GRUB in jessie supported these,
that I requested that `zpool create` no longer use "-d":
http://anonscm.debian.org/cgit/d-i/partman-zfs.git/commit/?id=46b42715da4ee17c95762129600958ff75f6d02d

GRUB *does* support feature@lz4_compress, but otherwise, only features
that are 'read-only compatible' according to zpool-features(7):
http://man.freebsd.org/zpool-features

Here is the list of "not read-only compatible' features that are
supported by GRUB - currently only lz4_compress:
http://anonscm.debian.org/cgit/pkg-grub/grub.git/tree/grub-core/fs/zfs/zfs.c#n277

The most problematic ones are hole_birth and embedded_data, because they
go "active" as soon as enabled.  Some of the others wouldn't initially
be a problem, until that functionality is used, but it's not safe to
enable those by default.

I think most of the new features are valuable and we should keep them if
possible, most certainly lz4_compress (which can be used to compress
metadata, even if you don't set compression=on for a dataset).  So I
suggest we use "-d" but still enable lz4 and all read-only compatible
features.  (`zpool create` without "-d" would enable *all* features by
default).

Thanks for reporting this!

Regards,
-- 
Steven Chamberlain
steven@pyro.eu.org