Operations grimoire/ZFS

ZFS pool administration

ZFS pool features

ZFS pools are versioned, so when we upgrade the OS (FreeBSD) or ZFS driver (Linux), we can get the new features:

   zpool upgrade -a

The only bad moment to do this is if you intend to use the pool elsewhere with a non-compatible ZFS implementation. For example, if you enable a feature in FreeBSD absent from ZFS on Linux, you wouldn't be able to directly mount in write the disk on a Linux machine. It's generally safe to do so, as we don't move pools from one OS to another.

Boot loader

Any pool with the bootfs property set is bootable. When a ZFS pool has new features enabled, you need to ensure the boot loader is still able to manage them.

On Linux, ZFS is supported by GRUB2, but not all the features. So you're safe as long as GRUB2 package is upgraded.

On FreeBSD, you can simply update the boot code. For Ysul for example:

   $ gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 ada0
   partcode written to ada0p1
   bootcode written to ada0

The -i argument here specifies the target partition to install the "partcode", gptzfsboot itself, ie the boot loader able to load the OS kernel on a ZFS pool. The bootcode is always installed at the start of the disk.

The protective MBR /boot/pmbr is optional but typically used. This bootstrap code is to search through the GPT table for a freebsd-boot partition and run the next bootstrap stage from it. That freebsd-boot partition then receives the gptboot (GPT with UFS disks) or gptzfsboot (GPT with ZFS disks).