u-boot & ZFS

[Mark Kettenis]

> Date: Wed, 18 Aug 2021 15:25:58 +0200
> From: ChrisO <armbian at osk.ch>
> 
> On Wed, Aug 18, 2021 at 12:26:11PM +0200, Lukasz Majewski wrote:
> > Hi ChrisO,
> > 
> > > On Tue, Aug 17, 2021 at 08:35:14PM -0400, Tom Rini wrote:
> > > > On Tue, Aug 17, 2021 at 06:03:10PM +0200, ChrisO wrote:
> > > >   
> > > > > Hi
> > > > > 
> > > > > I searched for u-boot ZFS references and all I found was several
> > > > > years old, but I suppose u-boot can cope with ZFS. So, my
> > > > > question is: is it possible to boot Linux from ZFS or at least
> > > > > boot from let's say SD-card with ext4 FS and mount a ZFS volume
> > > > > as root filesystem? I had a look at Armbian, installed all
> > > > > needed, user-space and kernel modules. After booting from SD card
> > > > > I can use ZFS on attached SATA SSD w/o any problem. I also see
> > > > > ZFS libs and kernel modules in initrd,  so it looks like the
> > > > > necessary things are there. Don't know where to start. I would be
> > > > > very thankful for any help.  
> > > > 
> > > > The general easy answer is to have /boot that is separate from the
> > > > rootfs and using a filesystem more commonly supported.
> > > > 
> > > > -- 
> > > > Tom  
> > > 
> > > Sounds like: go away kid, play with your old toys ;-)
> > > I was doing it the traditional way for long time, now wanted to try
> > > something new. Isn't it how we progress? I came to this list hoping
> > > to get an answer to my question. I know, most of you on this list
> > > have more important things to do. But giving me some advice could
> > > possibly result in me giving something back.
> > > 
> > 
> > Similar question I saw on OpenEmbedded/Yocto ML recenly. The answer
> > there was that "ZFS or ZOL is _not_ [*] commonly used on embedded
> > systems, so no support was needed" 
> > 
> > If find this topic interesting, then the community will try to help
> > when you provide any patches for review.
> > 
> > However, considering the above, it may be hard for any _exact_
> > guidelines.
> > 
> > 
> > Note:
> > [*] - Personally, I didn't saw any usage of ZFS on embedded systems.
> > 
> > > Thanks,
> > > Chris
> > 
> > 
> > 
> > 
> > Best regards,
> > 
> > Lukasz Majewski
> > 
> > --
> > 
> > DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> > Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma at denx.de
> 
> Hallo Lukasz
> 
> My system in question is not an embeded one. I just stated to play
> with an Odroid-HC4 and Armbian.
> It has two SATA connectors, boots from a SD card.
> All computer I use which have more than one disk connected are
> set-up with software RAID and LVM on top of it.
> ZFS has both build-in it's why I asked.
> Currently I have on this HC4 two partitions on each disk, the
> smaller ones are in RAID1 and host root FS, the bigger ones are in a
> mirrored Zpool. It works OK, it would be nicer to have just one
> filesystem, though.
> 
> Still not sure, it can or cannot be done?

My suggestion would be to use the EFI boot path with GRUB which
apparently can boot a Linux kernel from ZFS.  You'd still need a EFI
system partition with grub.efi on it, but that could live on the SD
card.