File:  [NetBSD Developer Wiki] / wikisrc / wiki / RootOnZFS.mdwn
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Sat Feb 22 19:17:04 2020 UTC (2 years, 4 months ago) by wiki
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    1: # Root On ZFS
    2: 
    3: NetBSD-9 gained much improved ZFS support.
    4: However, one feature it's still missing is the ability to have your system root on ZFS.
    5: For that, we need to teach our boot loader about ZFS, but until then we can work around this limitation by using a FFS boot partition and a ZFS root ramdisk.
    6: You'll also need to use NetBSD-9.99.47 or newer.
    7: 
    8: The idea is simple - the boot loader loads the NetBSD kernel from FFS and the ZFS root ramdisk.
    9: The ramdisk then mounts the boot partition and copies the requires ZFS modules from it into the ramdisk.
   10: ZFS is then initialised to load the modules and then umounts the boot partition.
   11: This step saves you from having to load the modules in boot.cfg.
   12: Because the initial root is on a ramdisk, we can then load the boot partition from inside the ZFS root to maintain it.
   13: 
   14: Once ZFS is initialised, the ZFS root is then mounted and sysctl then instructs init to chroot to it and the normal boot procedure then starts.
   15: Once started, the kernel and modules can updated by mounting the boot partition to /altroot.
   16: 
   17: ## Assumptions
   18: 
   19: The ramdisk does make some assumptions as there is no way to pass variables from boot.cfg:
   20: 
   21:   *  The boot partition can be referenced as `NAME=boot` - for GPT this is as simple as giving it a label.
   22:   *  The ZFS root pool is called `rpool` and the root filesystem is called `ROOT`.
   23: 
   24: ## Generic setup
   25: 
   26: Until the NetBSD installer can be updated, here are the manual steps from fresh:
   27: 
   28:   *  Build the ramdisk (`cd src/distrib/amd64/ramdisks/ramdisk-zfsroot; nbmake-amd64`)
   29:   *  Boot the NetBSD installer
   30:   *  Create a small (I used 2G) FFS partition and a normal swap partition
   31:   *  Create a partition for ZFS
   32:   *  Finish the NetBSD installation - install the etc, base and maybe rescue sets
   33:   *  Reboot into your minimal NetBSD install
   34:   *  Label the boot partition boot - if you don't do this then the ramdisk will moan it can't load modules
   35: 
   36: ## ZFS Setup
   37: 
   38: So far, so good. Now we need to make the needed adjustments to change root:
   39: 
   40:   *  Create a ZFS pool called `rpool` on your ZFS partition
   41:   *  Create a ZFS filesystem called `ROOT` in `rpool`
   42:   *  Set the mountpoint of `rpool/ROOT` to legacy so that the mount command can deal with it
   43:   *  Create any other ZFS filesystems you want to - if you create `/usr` or `/var` or anything in these they **must** to be legacy mount points as well
   44:   *  `zfs umount rpool/ROOT`
   45:   *  Add `rpool/ROOT /altroot zfs rw` to /etc/fstab
   46:   *  `mount /altroot`
   47:   *  Extract the sets you need to `/altroot`. At a minimum you will need etc and base.
   48:   *  Copy `/etc/wscons.conf`, `/etc/fstab` and any other config files sysinst might have created to `/etc/rc.conf` to `/altroot/etc`
   49:   *  Set `zfs=YES` in `/altroot/etc/rc.conf`
   50:   *  Remove `rpool/ROOT` from `/altroot/etc/fstab`
   51:   *  Add `name=boot /altroot ffs rw,noauto` to `/altroot/etc/fstab` along with any ZFS filesytems you created in '/usr' and '/var'
   52:   *  Add the filesystems as well to `critical_filesystems_local` in `/altroot/etc/rc.conf` - such as `critical_filesystems_local="/usr /var /var/log"`
   53:   *  Copy the `ramdisk-zfsroot.fs` to `/`
   54:   *  Edit `/boot.cfg` and add `menu=Boot ZFS Root:fs /ramdisk-zfsroot.fs;boot`
   55: 
   56: And done! You can now reboot and enjoy your root on ZFS and all the benefits it brings.
   57: When updating the kernel, remember to `mount /altroot` and update it there as well as the modules.
   58: 
   59: ## Future work
   60: 
   61: All these steps could be done in the installer.
   62: This is probably an easier task than adding ZFS support to the bootloader. But don't let that stop you if you are stuck for something to do!
   63: 
   64: # DANGER NETBSD ROOT ON ZFS USER, DANGER!
   65: 
   66: There seems to be an issue accessing `/dev` nodes on ZFS.
   67: While -current has enough fixes to work somewhat, accessing the boot partition whilst while root is on ZFS will hang, panic and maybe even corrupt your boot partition.
   68: As such, you'll have to reboot into single user. From here you can mount the ZFS partition to `/altroot` and copy the updated kernel and modules from there to the boot partition.
   69: Ironically, this is what the ramdisk approach was designed to actively avoid. Hopefully we can get it resolved soon.

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