Booting From a ZFS Root File System

Both SPARC based and x86 based systems boot with a boot archive, which is a file system image that contains the files required for booting. When booting from a ZFS root file system, the path names of both the boot archive and the kernel file are resolved in the root file system that is selected for booting.

Booting from a ZFS file system differs from booting from a UFS file system because with ZFS, a device specifier identifies a storage pool, not a single root file system. A storage pool can contain multiple bootable ZFS root file systems. When booting from ZFS, you must specify a boot device and a root file system within the pool that was identified by the boot device.

By default, the dataset selected for booting is the one identified by the pool's bootfs property. This default selection can be overridden by specifying an alternate bootable dataset that is included in the boot -Z command on a SPARC system or by selecting an alternate boot device from the BIOS on an x86 based system.

Booting From an Alternate Disk in a Mirrored ZFS Root Pool

You can attach a disk to create a mirrored ZFS root pool after installation. For more information about creating a mirrored root pool, see How to Configure a Mirrored Root Pool.

Review the following known issues regarding mirrored ZFS root pools:

If you replace a root pool disk by using the zpool replace command, you must install the boot information on the newly replaced disk by using the installboot or installgrub commands. If you create a mirrored ZFS root pool with the initial installation method or if you use the zpool attach command to attach a disk to the root pool, then this step is unnecessary. The installboot or installgrub command is as follows:
```
sparc# installboot -F zfs /usr/platform/`uname -i`/lib/fs/zfs/bootblk /dev/rdsk/c0t1d0s0
```
```
x86# installgrub /boot/grub/stage1 /boot/grub/stage2 /dev/rdsk/c0t1d0s0
```

You can boot from different devices in a mirrored ZFS root pool. Depending on the hardware configuration, you might need to update the PROM or the BIOS to specify a different boot device.

For example, you can boot from either disk (c1t0d0s0 or c1t1d0s0) in this pool.

# zpool status
  pool: rpool
 state: ONLINE
 scrub: none requested
config:

        NAME          STATE     READ WRITE CKSUM
        rpool         ONLINE       0     0     0
          mirror-0    ONLINE       0     0     0
            c1t0d0s0  ONLINE       0     0     0
            c1t1d0s0  ONLINE       0     0     0

On a SPARC based system, enter the alternate disk at the ok prompt.

ok boot /pci@7c0/pci@0/pci@1/pci@0,2/LSILogic,sas@2/disk@1

After the system is rebooted, confirm the active boot device. For example:

SPARC# prtconf -vp | grep bootpath
        bootpath:  '/pci@7c0/pci@0/pci@1/pci@0,2/LSILogic,sas@2/disk@1,0:a'

On an x86 based system, use syntax similar to the following:

x86# prtconf -v|sed -n '/bootpath/,/value/p'
        name='bootpath' type=string items=1
            value='/pci@0,0/pci8086,25f8@4/pci108e,286@0/disk@0,0:a'

On an x86 based system, select an alternate disk in the mirrored ZFS root pool from the appropriate BIOS menu.

Booting From a ZFS Root File System on a SPARC Based System

On a SPARC based system with multiple ZFS BEs, you can boot from any BE by using the beadm activate command.

During an installation and beadm activation process, the ZFS root file system is automatically designated with the bootfs property.

Multiple bootable datasets can exist within a pool. By default, the bootable dataset entry in the /pool-name/boot/menu.lst file is identified by the pool's bootfs property. However, a menu.lst entry can contain a bootfs command, which specifies an alternate dataset in the pool. In this way, the menu.lst file can contain entries for multiple root file systems within the pool.

When a system is installed with a ZFS root file system, an entry similar to the following is added to the menu.lst file:

title solaris
bootfs rpool/ROOT/solaris
title solaris-1
bootfs rpool/ROOT/solaris-1

When a new BE is created, the menu.lst file is updated automatically.

On a SPARC based system, two boot options are available:

After a ZFS BE is activated, you can use the boot -L command to display a list of bootable datasets within a ZFS pool. Then, you can select one of the bootable datasets in the list. Detailed instructions for booting that dataset are displayed. You can boot the selected dataset by following the instructions.
Use the boot -Z dataset command to boot a specific ZFS dataset.

Example 5-1 Booting From a Specific ZFS Boot Environment

If you have multiple ZFS BEs in a ZFS storage pool on your system's boot device, you can use the beadm activate command to specify a default BE.

For example, the following ZFS BEs are available as described by the beadm output:

# beadm list
BE        Active Mountpoint Space  Policy Created          
--        ------ ---------- -----  ------ -------          
solaris   -      -          19.18M static 2011-01-13 15:31 
solaris-1 NR     /          8.48G  static 2011-01-13 15:44

If you have multiple ZFS BEs on your SPARC based system, you can use the boot -L command. For example:

ok boot -L                                 
Boot device: /pci@0/pci@0/pci@2/scsi@0/disk@3,0:a  File and args: -L
1 solaris
2 solaris-1
Select environment to boot: [ 1 - 2 ]: 2

To boot the selected entry, invoke:
boot [<root-device>] -Z rpool/ROOT/solaris-1

Program terminated
ok boot -Z rpool/ROOT/solaris-1

Booting From a ZFS Root File System on an x86 Based System

The following entries are added to the /pool-name/boot/grub/menu.lst file during the installation process or beadm activate operation to boot ZFS automatically:

title Oracle Solaris 11 Express snv_152
findroot (pool_rpool,0,a)
bootfs rpool/ROOT/solaris
kernel$ /platform/i86pc/kernel/$ISADIR/unix -B $ZFS-BOOTFS
module$ /platform/i86pc/$ISADIR/boot_archive

If the device identified by GRUB as the boot device contains a ZFS storage pool, the menu.lst file is used to create the GRUB menu.

On an x86 based system with multiple ZFS BEs, you can select a BE from the GRUB menu. If the root file system corresponding to this menu entry is a ZFS dataset, the following option is added.

-B $ZFS-BOOTFS

Example 5-2 x86: Booting a ZFS File System

When booting from a ZFS file system, the root device is specified by the boot -B $ZFS-BOOTFS parameter. For example:

title Oracle Solaris 11 Express snv_152
findroot (pool_rpool,0,a)
bootfs rpool/ROOT/solaris
kernel$ /platform/i86pc/kernel/$ISADIR/unix -B $ZFS-BOOTFS
module$ /platform/i86pc/$ISADIR/boot_archive

Example 5-3 x86: Fast Rebooting a ZFS Root File System

The fast reboot feature provides the ability to reboot within seconds on x86 based systems. With the fast reboot feature, you can reboot to a new kernel without experiencing the long delays that can be imposed by the BIOS and boot loader. The ability to fast reboot a system drastically reduces down time and improves efficiency.

You must still use the init 6 command when transitioning between BEs with the beadm activate command. For other system operations where the reboot command is appropriate, you can use the reboot -f command. For example:

# reboot -f

Booting For Recovery Purposes in a ZFS Root Environment

Use the following procedure if you need to boot the system so that you can recover from a lost root password or similar problem.

If you need to recover a root pool or root pool snapshot, see Recovering the ZFS Root Pool or Root Pool Snapshots.

How to Boot ZFS for Recovery Purposes

Keep multiple boot environments to prevent a system boot failure. Follow these steps if your system won't boot because of a problem with the BE contents.

Boot from the Oracle Solaris 11 Express Live CD or from an Oracle Solaris 11 Express AI server.
At the terminal prompt, import the root pool.
```
# zpool import rpool
```
Mount the ZFS BE on /a
```
# beadm mount solaris-1 /a
```
Modify the BE contents to resolve the boot failure.
For example, review the menu.lst file to determine if the boot entries are correct.
```
# cat /a/rpool/boot/menu.lst
title solaris
bootfs rpool/ROOT/solaris
title solaris-1
bootfs rpool/ROOT/solaris-1
```
If a password or shadow entry is preventing a console login, then correct that problem.
```
# cd /a/etc
# vi passwd
```
If necessary, set the TERM type.
```
# TERM=vt100
# export TERM
```
Update the boot archive
```
# bootadm update-archive -R /a
```
Reboot the system.
```
# init 6
```

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