u-boot & ZFS

u-boot & ZFS

[ChrisO]

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.

Regards.
Chris

Re: u-boot & ZFS

[Tom Rini]

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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

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Re: u-boot & ZFS

[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.

Thanks,
Chris

Re: u-boot & ZFS

[Lukasz Majewski]

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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@denx.de

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Re: u-boot & ZFS

[ChrisO]

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@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?

Thanks and regards,
Chris

Re: u-boot & ZFS

[Tom Rini]

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On Wed, Aug 18, 2021 at 03:25:58PM +0200, ChrisO wrote:
> 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@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?

The answer is that yes, today we have zfs support in U-Boot.  And it
would be great if someone wanted to actively test and maintain it.  That
I had to double check just now that the patches you mentioned had been
merged should also speak to the potential state of the code.

-- 
Tom

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Re: u-boot & ZFS

[ChrisO]

On Wed, Aug 18, 2021 at 09:53:06AM -0400, Tom Rini wrote:
> On Wed, Aug 18, 2021 at 03:25:58PM +0200, ChrisO wrote:
> > 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@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?
> 
> The answer is that yes, today we have zfs support in U-Boot.  And it
> would be great if someone wanted to actively test and maintain it.  That
> I had to double check just now that the patches you mentioned had been
> merged should also speak to the potential state of the code.
> 
> -- 
> Tom

Hi Tom

This is a great news! 
I am a very old, retired Solaris/Linux admin I don't think I would be still able to dive into u-boot development.
Other than this, I would try to do my best to help.

Regards,
Chris

Re: u-boot & ZFS

[Mark Kettenis]

> Date: Wed, 18 Aug 2021 15:25:58 +0200
> From: ChrisO <armbian@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@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.

Re: u-boot & ZFS

[Dimitri John Ledkov]

On Wed, Aug 18, 2021 at 2:26 PM ChrisO <armbian@osk.ch> wrote:
>
> 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@denx.de
>
> Hallo Lukasz
>
> My system in question is not an embeded one. I just stated to play with an Odroid-HC4 and Armbian.

4GB of RAM sounds way too little for zfs.

> 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?
>
> Thanks and regards,
> Chris

-- 
Regards,

Dimitri.

Re: u-boot & ZFS

[ChrisO]

On Wed, Aug 18, 2021 at 03:12:04PM +0100, Dimitri John Ledkov wrote:
> On Wed, Aug 18, 2021 at 2:26 PM ChrisO <armbian@osk.ch> wrote:
> >
> > 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@denx.de
> >
> > Hallo Lukasz
> >
> > My system in question is not an embeded one. I just stated to play with an Odroid-HC4 and Armbian.
> 
> 4GB of RAM sounds way too little for zfs.

Because ...
I don't want to keep my ZFS pool in RAM, it contains two disk partitions ~220GB and its usage of memory
for its cache, ARC (adaptive replacement cache) is:

root@odroidhc4:~# awk '/^size/ { print $1 " " $3 / 1048576 " MB" }' < /proc/spl/kstat/zfs/arcstats
size 5.91608 MB

I did administer, in another life ;-) large Solaris servers on ZFS only and never had mamory usage problems.

Thanks and regards,
Chris

> 
> > 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?
> >
> > Thanks and regards,
> > Chris
> 
> -- 
> Regards,
> 
> Dimitri.