Difference between revisions of "ZFS on Boot"

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  # cd $your-zfs-source-area
  # cd $your-zfs-source-area
===== Install ZFS by getting sources ======
===== Install ZFS by getting sources =====
  # Insert lines here, git clone, etc
  # Insert lines here, git clone, etc
===== Install ZFS continued ... ======
===== Install ZFS continued ... =====
  # cd spl
  # cd spl

Revision as of 00:55, 7 July 2016

ZFS as Boot

  Status: Beta
  Most of the commands listed below must be run as root or with sudo.

Because you have to compile own kexts, they will not be signed. SIP needs to be disabled for Kext signing to work. The next OpenZFSOnOSX will come with --enable-boot compiled KEXTs and be signed.

Disk Layout

Play disk: disk1

I used gptfdisk, but gpt and diskutil can be used also. Create the following partitions on the test boot disk:

  Disk /dev/rdisk1: 83886080 sectors, 40.0 GiB
  Number  Start (sector)    End (sector)  Size       Code  Name
  1            2048          411647   200.0 MiB   EF00  EFI System
  2          411648        82200575   39.0 GiB    BF01  rpool
  3        82200576        83886046   823.0 MiB   AB00  Apple boot

s1 is not really used, but added for EFI.

s2 is the ZFS pool used for booting. Note: You are not limited to using the name rpool.

s3 is the small HFS boot which will carry the prelinkedkernel to load the kernel with ZFS.

The layout need not be exactly this, but:

The EFI partition should always exist at the beginning of the disk.

The Apple Boot (ab00) partition should directly follow the ZFS partition, and while it can be as small as 50 MB, it is better to use 650MB or more (to imitate a Recovery HD).

  Note: at this time, the boot helper partition is not updated by the OS
  and must be manually updated. It may be possible to script this in a
  launchd service, or even 'bless' the device so that macOS updates
  it automatically. Additional development is ongoing.
  You cannot use Startup Disk to select the boot disk, see blessing the boot device.

Populating the ZFS Root s2

Root pool

Any pool name may be used - rpool is used here for example. Additional research is needed on atime, casesensitivity, and normalization (and probably more).

# sudo zpool create -f -o ashift=12 -O casesensitivity=insensitive \
 -O normalization=formD -O atime=off -O compression=lz4 \
 -O mountpoint=none -O canmount=off rpool disk1s2

This step will relabel the disks using InvariantDisks paths (by UUID), so they can be located at boot time.

# sudo zpool export rpool
# sudo zpool import -d /var/run/disk/by-id rpool
  We strongly recommend NOT using /dev/disk paths due to disk renumbering issues!

Root dataset

  Note: com.apple.mimic_hfs is known to NOT be compatible at this time. (It will panic!)

Create ROOT and lower just like IllumOS so that you can easy swap OS snapshots and reboot into something else (for example to run softwareupdate).

# sudo zfs create -o mountpoint=none -o canmount=off rpool/ROOT
# sudo zfs create -o mountpoint=legacy rpool/ROOT/Capitan
# sudo zpool set bootfs=rpool/ROOT/Capitan rpool

You probably want to relocate your home folder outside of the root dataset, for example rpool/HOME/username, or on ZVOL for compatibility.

# sudo zfs create -o mountpoint=/Users -o canmount=off rpool/HOME
# sudo zfs create rpool/HOME/username

Mount it:

# sudo mkdir /Volumes/Capitan
# sudo mount_zfs rpool/ROOT/Capitan /Volumes/Capitan

Install macOS

Copy over the OS as you see fit, rsync will generally do. (Remember that etc, tmp and var are symlinks into /private)

# rsync -axH --exclude=".Spotlight-V100" --exclude=".fseventsd" \
 --exclude=".vol" / /Volumes/Capitan/

Install ZFS

# sudo mkdir -p /Volumes/Capitan/usr/local
# cd /Volumes/Capitan/usr/local
# sudo ln -s ../../sbin sbin

Install ZFS with own source repository
# cd $your-zfs-source-area
Install ZFS by getting sources
# Insert lines here, git clone, etc
Install ZFS continued ...
# cd spl
# git fetch --all
# git checkout spl-boot
# ./autogen
# ./configure --enable-boot
# make
# sudo make install DESTDIR=/Volumes/Capitan
# cd ../zfs
# git fetch --all
# git checkout ldi-boot
# ./autogen
# ./configure --enable-boot 
# make
# sudo make install DESTDIR=/Volumes/Capitan

Or use a stage directory for zfs builds, that can also be done.

# make install DESTDIR=/stage_dir
# rsync -acH /stage_dir/ /Volumes/Capitan/

Setting up boot slice s3


Journaled HFS+ filesystem, and populated thusly; (Volume named boot here) These can be rsynced from the (normal) booted OS, or from the Capitan mount.

# newfs_hfs -J -v "boot" /dev/disk1s3
# diskutil mount disk1s3
# sudo mdutil -i off /Volumes/boot


# sudo mkdir -p /Volumes/boot/System/Library/CoreServices
# sudo mkdir -p /Volumes/boot/com.apple.boot.R/System/Library/PrelinkedKernels
# sudo mkdir -p /Volumes/boot/com.apple.boot.R/Library/Preferences/SystemConfiguration
# sudo mkdir -p /Volumes/boot/com.apple.boot.R/usr/standalone/i386

Required Files

# sudo rsync -a /Volumes/Capitan/System/Library/CoreServices/PlatformSupport.plist \
# sudo rsync -a /Volumes/Capitan/System/Library/CoreServices/SystemVersion.plist \
# sudo rsync -a /Volumes/Capitan/System/Library/PrelinkedKernels/prelinkedkernel \
# sudo rsync -a /Volumes/Capitan/Library/Preferences/SystemConfiguration/com.apple.Boot.plist \
# sudo rsync -a /Volumes/Capitan/usr/standalone/i386/ \

Bless the volume

The boot helper needs to know where to load boot.efi from.

You may use any label in place of ZFS Boot here, it will appear at the option-boot screen.

# sudo bless --folder /Volumes/boot/System/Library/CoreServices \
  --file /Volumes/boot/System/Library/CoreServices \
  --bootefi /Volumes/Capitan/System/Library/CoreServices/boot.efi \
  --label "ZFS Boot"

This step does not change the current boot device, unless you add --setBoot. See blessing the boot device to change the startup device.

Edit Boot.plist

More examples of the Boot.plist can be found at com.apple.Boot.plist

# sudo vim /Volumes/boot/com.apple.boot.R/Library/Preferences/SystemConfiguration/com.apple.Boot.plist

Two keys must be set: Kernel Flags and Root UUID:

Look for

  <key>Kernel Flags</key>

Replace with:

  <key>Kernel Flags</key>
  <string>-v keepsyms=y zfs_boot=rpool</string>
  <key>Root UUID</key>

Any UUID may be used here, I used 5A465320-626F-6F74-2064-657669636500, (which is literally the string "ZFS boot device\0").

See Boot.plist for more examples.

ZVOL boot from HFS+ can be accomplished by using the UUID of the partition containing a standard Mac OS install, for compatibility.

Generate prelinkedkernel

Generate caches for kernel

# kextcache -arch x86_64 -local-root -volume-root /Volumes/rpool \
  -kernel /Volumes/rpool/System/Library/Kernels/kernel \
  -prelinked-kernel /Volumes/rpool/System/Library/PrelinkedKernels/prelinkedkernel \
  -- /Volumes/rpool/System/Library/Extensions /Volumes/boot/Library/Extensions

For developers who also have development, or debug kernels, do the same for each one. For example, caches for kernel.development

# kextcache -arch x86_64 -local-root -volume-root /Volumes/rpool \
  -kernel /Volumes/rpool/System/Library/Kernels/kernel.development \
  -prelinked-kernel /Volumes/rpool/System/Library/PrelinkedKernels/prelinkedkernel.development \
  -- /Volumes/rpool/System/Library/Extensions /Volumes/boot/Library/Extensions

Set the boot device

Finally, tell your Mac to use the boot helper on boot. You may want to try the --nextonly’’’ option to avoid permanent changes.

# sudo bless --device disk1s3 --setBoot


Booting on ESX

This is only required if you prefer not to bless the device. If you bless it, it will boot automatically. However, if you skip the blessing part you can easily chose which HDD to boot by using the EFI Boot Shell.

Booting on ESX, hit F2 to get the EFI menu up. One of the options is the "EFI Shell (not supported)". Once the EFI shell has been entered

# map

will list all available maps. For me,

fs0 disk0 EFI partition
fs1 disk0 OSX boot
fs2 disk0 OSX Recovery
fs3 disk1 EFI
fs4 disk1 boot HFS
fs5 disk1 recovery
fs6 disk1 ZFS

So in my case

EFI> fs4:
fs4: ls
usr System Library
fs4: cd System 
fs4: cd Library
fs4: cd CoreServices
fs4: boot.efi

Which runs (boots) boot.efi, which then locates and loads the prelinkedkernel. You can specify boot options here too:

fs4: boot.efi zfs_boot=rpool -s -v

To ask it to boot from pool rpool (using bootfs= property) into single-user mode, with verbose output.

Booting on VirtualBox

SIP can be disabled in VirtualBox, but must be disabled before every boot. One way to do this is to install rEFInd into the EFI partition. It is possible to write a startup.nsh script to do so.

VirtualBox does not like the boot helper as created above. It used to function in a previous version (4.3.x?) but at this time, the easiest option I have found is to clone the contents of BaseSystem.dmg from any MacOS recovery partition.

# diskutil mount disk0s3
# hdiutil attach -readonly "/Volumes/Recovery HD/com.apple.recovery.boot/BaseSystem.dmg"


# sudo rsync -axH "/Volumes/OS X Base System/" "/Volumes/boot/"

Or if you prefer asr:

# sudo asr restore -source "/Volumes/OS X Recovery" -target "/Volumes/boot" -erase
# diskutil rename "/Volumes/OS X Base System 1" "boot"

And the paths used above will change, as we are using a “real” disk layout with no com.apple.boot.R:

# sudo rsync -a /Volumes/Capitan/System/Library/PrelinkedKernels/prelinkedkernel \
# sudo vim /Volumes/boot/Library/Preferences/SystemConfiguration/com.apple.Boot.plist

(See Boot.plist)

Booting on real Macs

  Always make extra backups!
  Test this out using flash drives first!

Create partitions as above. If you already created a boot helper on one disk, you can clone it with Disk Utility or asr and edit the [com.apple.Boot.plist] to put a different pool name in zfs_boot in the Kernel flags.

Hold option while powering on or restarting your Mac.

Look for ZFS Boot as set by bless --label above, and double click.

ZFS will load and search available disks for the pool specified in zfs_boot above. If the pool is not found, or not enough disks are present, ZFS will wait and check additional disks as they appear.

If all is well, the pool will import and MacOS will boot from the Capitan dataset.

After a certain number of attempts, the MacOS loader will show a 'prohibitory symbol' (circle with a line through it). If you see this, hold the power button until your Mac powers off.

If you are stuck in a boot loop, power the machine off, then power on while holding the option key. Select the partition with standard MacOS to reboot normally. Once booted, check and set System Preferences->Startup Disk.


Mounting other boot environments

# sudo zfs snapshot rpool/ROOT/Capitan1@updating
# sudo zfs clone rpool/ROOT/Capitan1@updating rpool/ROOT/Capitan2
# mkdir /Volumes/Capitan2
# sudo mount_zfs rpool/ROOT/Capitan2 /Volumes/Capitan2

Later you can promote

# sudo zfs promote rpool/ROOT/Capitan2

Then if you want

# sudo zfs destroy -r rpool/ROOT/Capitan

Blessing the boot device

Need only be run once, to setup the boot volume:

# sudo bless --folder /Volumes/boot/System/Library/CoreServices \
  --file /Volumes/boot/System/Library/CoreServices/boot.efi \
  --bootefi /Volumes/Capitan/System/Library/CoreServices/boot.efi

This command actually sets the boot helper to be used on reboot:

# sudo bless --device disk1s3 --setBoot