grub-pc, grub2 doesn't check /dev/disk/by-id or "by-path" for zfs zpool

[brian mullan]

When creating an Ubuntu 16.04 root install on a zfs using disks & zfs pool created using "/dev/disk/by-id" and I get to the point of running:

          apt install grub-pc

I select the 4 disks I am putting into the ZFS pool to have grub installed into but grub-pc fails (see attached screen shot):

Note: first problem is that "menu" presented by grub-pc lists them as

/dev/sda
/dev/sdb
/dev/sdc
/dev/sdd

I think they should be listed as their "by-id" or "by-path" ... if you created the zfs disks and pool with that!

In my case the disks were created/partitioned using:

sgdisk -Z -n9:-8M:0 -t9:bf07 -c9:Reserved -n2:-8M:0 -t2:ef02 -c2:GRUB -n1:0:0 -t1:bf01 -c1:ZFS \
        /dev/disk/by-id/ata-ST2000DM001-1CH164_W1E8JLV9

sgdisk -Z -n9:-8M:0 -t9:bf07 -c9:Reserved -n2:-8M:0 -t2:ef02 -c2:GRUB -n1:0:0 -t1:bf01 -c1:ZFS \
        /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E0713E

sgdisk -Z -n9:-8M:0 -t9:bf07 -c9:Reserved -n2:-8M:0 -t2:ef02 -c2:GRUB -n1:0:0 -t1:bf01 -c1:ZFS \
        /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E084AP

sgdisk -Z -n9:-8M:0 -t9:bf07 -c9:Reserved -n2:-8M:0 -t2:ef02 -c2:GRUB -n1:0:0 -t1:bf01 -c1:ZFS \
        /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E06YPY

later I use this command to created the ZFS Pool of 2 mirrors each with 2 HDs using "by-id".

zpool create -o ashift=12 -O atime=off -O canmount=off -O compression=lz4 \
     -O normalization=formD -O mountpoint=/ -R /mnt rpool mirror \
     /dev/disk/by-id/ata-ST2000DM001-1CH164_W1E8JLV9-part1 \
     /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E0713E-part1 \
     mirror /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E084AP-part1 \
     /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E06YPY-part1 -f

And confirm the ZFS pool is created correctly by:

      zpool status

which DOES and the above shows the disks "by-id" and NOT as sda, sdb, sdc, sdd

But later in the process when running "apt install grub-pc" the disks are listed as /dev/sda, /dev/sdb etc.

The grub-pc "form" where you select where to install should probably look something like if the disks were created "by-id":

     [ ] /dev/disk/by-id/ata-ST2000DM001-1CH164_W1E8JLV9
     [ ] /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E0713E
     [ ] /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E084AP
     [ ] /dev/disk/by-id/ata-ST2000DM001-9YN164_Z1E06YPY

I did find a thread online where there is/was alot of discussion about this problem!

     https://github.com/zfsonlinux/grub/issues/5

Some work-arounds were suggested but also some where discussing the root cause.

I think in 16.04 this Grub problem still exists.

My reasoning is that despite how I created the disks & the pool when I ran "apt install grub-pc" it lists the choices as /dev/sda, /dev/sdb etc.

And if I just go ahead and select those disks (I figured why not try and see what happens right?) then I get the errors shown in the attached screen shot.

This "may" be a zfsonlinux BUG but since Ubuntu is now supporting ZFS I figured I'd report it here so others encountering it know what is going on.

Lastly...

I would suggest that the current Ubuntu Documentation on this is incorrect:

https://wiki.ubuntu.com/Kernel/Reference/ZFS

The Ubuntu ZFS documentation says:

ZFS Pools

A zpool is a pool of storage made from a collection of VDEVS. One or more ZFS file systems can be created from a ZFS pool.

In the following example, a pool named "pool-test" is created from 3 physical drives:

$ sudo zpool create pool-test /dev/sdb /dev/sdc /dev/sdd

Striping is performed dynamically, so this creates a zero redundancy RAID-0 pool.

Notice: If you are managing many devices, it can be easy to confuse them, so you should probably prefer /dev/disk/by-id/ names, which often use serial numbers of drives. The examples here should not suggest that 'sd_' names are preferred. They merely make examples herein easier to read.

THE ABOVE Notice I think is inaccurate in suggesting "you should probably prefer"... from all the documentation and examples I have found including the official example for installing

Ubuntu 16.04 Root on ZFS:
https://github.com/zfsonlinux/zfs/wiki/Ubuntu%2016.04%20Root%20on%20ZFS

Where in "2.2 Partition your disk" it says:

"Always use the long /dev/disk/by-id/* aliases with ZFS. Using the /dev/sd* device nodes
directly can cause sporadic import failures, especially on systems that have more than one storage pool."

[brian mullan (bmullan)]

added some updated info.

[Steve Langasek (vorlon)]

Ubuntu 16.04 does not support root on zfs. Marking as wishlist.

[brian mullan (bmullan)]

Steve
Thx but so far I and others are installing Ubuntu 16.04 root on zfs and it runs ok.

I think I even included the zfsonlinux guide in the orig report.

I think the only real problem I've had is this issue with grub-pc not parsing ZFS disks "by-id".

[brian mullan (bmullan)]

Just heard from a Reddit zfs thread inquery I made that the fix for grub & zfs is aleady in 16.10 & will make it into 16.04 in perhaps a month..

The fix is being tracked with this bug:

https://bugs.launchpad.net/ubuntu/xenial/+source/grub2/+bug/1527727

So my bug report can be closed.