Info working ZFS realisations

[f-andrey]

May be you interesting in ZFS analog

https://docs.oracle.com/cd/E26502_01/html/E29031/beadm-1m.html (integrated grub, seems to have been https://launchpad.net/beadm)
https://github.com/vermaden/beadm
https://github.com/freebsd/freebsd/tree/master/sbin/bectl

https://is.gd/BECTL - presentation beadm and bectl

[laenion]

Indeed, there seem to be a lot of similarities between beadm and transactional-update, just that beadm is using ZFS instead of Btrfs.
That said: ZFS has all the features required by transactional-update; even GRUB2 support for ZFS snapshots seems to be available. So if anybody is interested in implementing ZFS support please feel free to do so.

One thing I should note about the presentation: On page 40 it is claimed that a "complete system rollback, restoring the complete system to the identical state as it was in when a snapshot was taken, is not possible" with Btrfs / openSUSE. This is not a limitation of Btrfs, but an intentional design decision: If directories like /var would be part of the snapshot, then a rollback would roll back production data accumulated since taking the snapshot - which is most likely not what anybody would want. For that reason certain directories are excluded from the snapshot by creating separate subvolumes.

[f-andrey]

Yes in ZFS BE save not all data, only content/datasets zroot/ROOT/ page 42-45
/var and /var/... very discussion, not all content not dependent, for example pkg base

[vermaden]

Hi,

author of https://github.com/vermaden/beadm and https://is.gd/BECTL presentation here.

For the record, I got similar question on my blog and this is the answer:
https://vermaden.wordpress.com/2018/11/15/zfs-boot-environments-reloaded-at-nluug-autumn-conference-2018/#comment-15782

I will copy it here so you will not have to visit my terrible blog :)

FreeBSD by default omits these dirs in ZFS Boot Environments protection:

• /tmp
• /usr/home
• /usr/ports
• /usr/src
• /var/audit
• /var/crash
• /var/log
• /var/mail
• /var/tmp

So no real ‘data’ here besides /home (by default as /usr/home on FreeBSD) – but beadm(8) is here to protect the system and its services – not users data. So on FreeBSD besides users home directories WHOLE SYSTEM along with daemons/services/data is protected by default.

These are excludes from OpenSUSE Leap 15 Linux system:

• /boot/grub2.*
• /home
• /opt
• /var/opt
• /srv
• /usr/local
• /tmp
• /var/tmp
• /var/log
• /var/cache
• /var/crash
• /var/lib/libvirt/images
• /var/lib/mailman
• /var/spool
• /var/lib/named
• /var/lib/mariadb
• /var/lib/mysql
• /var/lib/pgqsl

This means that system can be screwed from the beginning (/boot/grub2.*) along with broken services/daemons/applications (/opt and /srv and /usr/local omitted). Not to mention ‘picky’ excludes for mariadb/mysql/pgsql dirs, why sqlite/db2/informix/mongodb/… directories are not omitted?

I am also curious what Ubuntu 19.10 will bring as it will be shipped with root on ZFS feature … but as I know the Linux world the /boot partition will be separate anyway with some ext4/xfs filesystem so the whole idea of protection of the whole system will be dead on day one.

Hope that helps.

Regards.

[laenion]

Yes, that was me in the blog - of course I'm always interested in seeing how other systems are solving the same task :-)

Regarding the subvolume layout I should note that the above list for Leap is not up to date any more, I've opened https://bugzilla.opensuse.org/show_bug.cgi?id=1151714 to fix the documentation. We have a unified /var subvolume now.

Regarding /boot: When using Btrfs on openSUSE /boot will usually be part of the root file system for exactly that reason: Protect the system as a whole. The exception you are talking about is /boot/grub2/<arch>, which has to match the version installed into the MBR / EFI. Because of that, this, and only this, directory is created as a separate subvolume.

However for transactional-update all of this is not relevant: ZFS should provide all the necessary features required for transactional-update support.