[Bug 1867007] [NEW] ZFS won't boot if multiple rpools found

[Kevin Menard]

Public bug reported:

I had an Ubuntu old installation that used a ZFS root, using the layout
described in the ZFS on Linux docs. Consequently, the pool name for my
Ubuntu installation was "rpool". I'm currently encountering an issue
with that pool that only allows me to mount it read-only. So, I'd like
to replicate the datasets from there to a new device.

On the new device, I've set up a ZFS system using the Ubuntu 20.04 daily
installer (March 9, 2020). This setup creates a new pool named "rpool".
So, with both devices inserted, I have two distinct pools each named
"rpool", one of which will kernel panic if I try to mount it read-write.

ZFS is fine with having multiple pools with the same name. In these
cases, you use `zfs import` with the pool's GUID and give it a distinct
pool name on import. However, the grub config for booting from ZFS
doesn't appear to handle multiple pools with the same rpool name very
well. Rather than using the pool's GUID, it uses the name, and as such,
it's unable to boot properly when another pool with the name "rpool" is
attached to the system.

I think it'd be better if the config were written in such a way that
`update-grub` generated boot config bound to whatever pool it found at
the time of its invocation, and not start searching through all pools
dynamically upon boot. Just to be clear, I have an Ubuntu 20.04 system
with a ZFS root that boots just fine. But, the moment I attach the old
pool, also named "rpool", I'm no longer able to boot up my system even
though I haven't removed the good pool and I haven't re-run `update-
grub`. Instead of botoing, I'm thrown into the grub command line.

** Affects: grub2 (Ubuntu)
     Importance: Undecided
         Status: New

** Description changed:

  I had an Ubuntu old installation that used a ZFS root, using the layout
  described in the ZFS on Linux docs. Consequently, the pool name for my
  Ubuntu installation was "rpool". I'm currently encountering an issue
  with that pool that only allows me to mount it read-only. So, I'd like
  to replicate the datasets from there to a new device.
  
  On the new device, I've set up a ZFS system using the Ubuntu 20.04 daily
  installer (March 9, 2020). This setup creates a new pool named "rpool".
  So, with both devices inserted, I have two distinct pools each named
  "rpool", one of which will kernel panic if I try to mount it read-write.
  
  ZFS is fine with having multiple pools with the same name. In these
  cases, you use `zfs import` with the pool's GUID and give it a distinct
  pool name on import. However, the grub config for booting from ZFS
  doesn't appear to handle multiple pools with the same rpool name very
  well. Rather than using the pool's GUID, it uses the name, and as such,
  it's unable to boot properly when another pool with the name "rpool" is
  attached to the system.
  
  I think it'd be better if the config were written in such a way that
  `update-grub` generated boot config bound to whatever pool it found at
  the time of its invocation, and not start searching through all pools
  dynamically upon boot. Just to be clear, I have an Ubuntu 20.04 system
  with a ZFS root that boots just fine. But, the moment I attach the old
  pool, also named "rpool", I'm no longer able to boot up my system even
  though I haven't removed the good pool and I haven't re-run `update-
- grup`. Instead of botoing, I'm thrown into the grub command line.
+ grub`. Instead of botoing, I'm thrown into the grub command line.

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https://bugs.launchpad.net/bugs/1867007

Title:
  ZFS won't boot if multiple rpools found

Status in grub2 package in Ubuntu:
  New

Bug description:
  I had an Ubuntu old installation that used a ZFS root, using the
  layout described in the ZFS on Linux docs. Consequently, the pool name
  for my Ubuntu installation was "rpool". I'm currently encountering an
  issue with that pool that only allows me to mount it read-only. So,
  I'd like to replicate the datasets from there to a new device.

  On the new device, I've set up a ZFS system using the Ubuntu 20.04
  daily installer (March 9, 2020). This setup creates a new pool named
  "rpool". So, with both devices inserted, I have two distinct pools
  each named "rpool", one of which will kernel panic if I try to mount
  it read-write.

  ZFS is fine with having multiple pools with the same name. In these
  cases, you use `zfs import` with the pool's GUID and give it a
  distinct pool name on import. However, the grub config for booting
  from ZFS doesn't appear to handle multiple pools with the same rpool
  name very well. Rather than using the pool's GUID, it uses the name,
  and as such, it's unable to boot properly when another pool with the
  name "rpool" is attached to the system.

  I think it'd be better if the config were written in such a way that
  `update-grub` generated boot config bound to whatever pool it found at
  the time of its invocation, and not start searching through all pools
  dynamically upon boot. Just to be clear, I have an Ubuntu 20.04 system
  with a ZFS root that boots just fine. But, the moment I attach the old
  pool, also named "rpool", I'm no longer able to boot up my system even
  though I haven't removed the good pool and I haven't re-run `update-
  grub`. Instead of botoing, I'm thrown into the grub command line.

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