Using ZFS on a Solaris System With Zones Installed

The following sections describe how to use ZFS on a system with Oracle Solaris zones:

• Adding ZFS File Systems to a Non-Global Zone

• Delegating Datasets to a Non-Global Zone

• Adding ZFS Volumes to a Non-Global Zone

• Using ZFS Storage Pools Within a Zone

• Managing ZFS Properties Within a Zone

• Understanding the zoned Property

Keep the following points in mind when associating ZFS datasets with zones:

• You can add a ZFS file system or a clone to a non-global zone with or without delegating administrative control.

• You can add a ZFS volume as a device to non-global zones.

• You cannot associate ZFS snapshots with zones at this time.

In the following sections, a ZFS dataset refers to a file system or a clone.

Adding a dataset allows the non-global zone to share disk space with the global zone, though the zone administrator cannot control properties or create new file systems in the underlying file system hierarchy. This operation is identical to adding any other type of file system to a zone and should be used when the primary purpose is solely to share common disk space.

ZFS also allows datasets to be delegated to a non-global zone, giving complete control over the dataset and all its children to the zone administrator. The zone administrator can create and destroy file systems or clones within that dataset, as well as modify properties of the datasets. The zone administrator cannot affect datasets that have not been added to the zone, including exceeding any top-level quotas set on the delegated dataset.

Consider the following when working with ZFS on a system with Oracle Solaris zones installed:

• A ZFS file system that is added to a non-global zone must have its mountpoint property set to legacy.

• Due to CR 6449301, do not add a ZFS dataset to a non-global zone when the non-global zone is configured. Instead, add a ZFS dataset after the zone is installed.

• When both a source zonepath and a target zonepath reside on a ZFS file system and are in the same pool, zoneadm clone will now automatically use the ZFS clone to clone a zone. The zoneadm clone command will create a ZFS snapshot of the source zonepath and set up the target zonepath. You cannot use the zfs clone command to clone a zone. For more information, see Part II, Oracle Solaris Zones, in System Administration Guide: Oracle Solaris Zones, Oracle Solaris 10 Containers, and Resource Management.

Adding ZFS File Systems to a Non-Global Zone

You can add a ZFS file system as a generic file system when the goal is solely to share space with the global zone. A ZFS file system that is added to a non-global zone must have its mountpoint property set to legacy. For example, if the tank/zone/zion file system will be added to a non-global zone, set the mountpoint property in the global zone as follows:

# zfs set mountpoint=legacy tank/zone/zion

You can add a ZFS file system to a non-global zone by using the zonecfg command's add fs subcommand.

In the following example, a ZFS file system is added to a non-global zone by a global zone administrator from the global zone:

# zonecfg -z zion
zonecfg:zion> add fs
zonecfg:zion:fs> set type=zfs
zonecfg:zion:fs> set special=tank/zone/zion
zonecfg:zion:fs> set dir=/export/shared
zonecfg:zion:fs> end

This syntax adds the ZFS file system, tank/zone/zion, to the already configured zion zone, which is mounted at /export/shared. The mountpoint property of the file system must be set to legacy, and the file system cannot already be mounted in another location. The zone administrator can create and destroy files within the file system. The file system cannot be remounted in a different location, nor can the zone administrator change properties on the file system such as atime, readonly, compression, and so on. The global zone administrator is responsible for setting and controlling properties of the file system.

For more information about the zonecfg command and about configuring resource types with zonecfg, see Part II, Oracle Solaris Zones, in System Administration Guide: Oracle Solaris Zones, Oracle Solaris 10 Containers, and Resource Management.

Delegating Datasets to a Non-Global Zone

To meet the primary goal of delegating the administration of storage to a zone, ZFS supports adding datasets to a non-global zone through the use of the zonecfg command's add dataset subcommand.

In the following example, a ZFS file system is delegated to a non-global zone by a global zone administrator from the global zone.

# zonecfg -z zion
zonecfg:zion> add dataset
zonecfg:zion:dataset> set name=tank/zone/zion
zonecfg:zion:dataset> end

Unlike adding a file system, this syntax causes the ZFS file system tank/zone/zion to be visible within the already configured zion zone. The zone administrator can set file system properties, as well as create descendent file systems. In addition, the zone administrator can create snapshots and clones, and otherwise control the entire file system hierarchy.

Adding ZFS Volumes to a Non-Global Zone

You can add or create a ZFS volume in a non-global zone or you can add access to a volume's data in a non-global zone in the following ways:

• In a non-global zone, a privileged zone administrator can create a ZFS volume as descendent of a previously delegated file system. For example:

  # zfs create -V 2g tank/zone/zion/vol1

  The above syntax means that the zone administrator can manage the volume's properties and data in the non-global zone.

• In a global zone, use the zonecfg add dataset subcommand and specify a ZFS volume to be added to a non-global zone. For example:

  # zonecfg -z zion
  zonecfg:zion> add dataset
  zonecfg:zion:dataset> set name=tank/volumes/vol1
  zonecfg:zion:dataset> end

  The above syntax means that the zone administrator can manage the volume's properties and data in the non-global zone.

• In a global zone, use the zonecfg add device subcommand and specify a ZFS volume whose data can be accessed in a non-global zone. For example:

  # zonecfg -z zion
  zonecfg:zion> add device
  zonecfg:zion:device> set match=/dev/zvol/dsk/tank/volumes/vol2
  zonecfg:zion:device> end

  The above syntax means that only the volume data can be accessed in the non-global zone.

Using ZFS Storage Pools Within a Zone

ZFS storage pools cannot be created or modified within a zone. The delegated administration model centralizes control of physical storage devices within the global zone and control of virtual storage to non-global zones. Although a pool-level dataset can be added to a zone, any command that modifies the physical characteristics of the pool, such as creating, adding, or removing devices, is not allowed from within a zone. Even if physical devices are added to a zone by using the zonecfg command's add device subcommand, or if files are used, the zpool command does not allow the creation of any new pools within the zone.

Managing ZFS Properties Within a Zone

After a dataset is delegated to a zone, the zone administrator can control specific dataset properties. After a dataset is delegated to a zone, all its ancestors are visible as read-only datasets, while the dataset itself is writable, as are all of its descendents. For example, consider the following configuration:

global# zfs list -Ho name
tank
tank/home
tank/data
tank/data/matrix
tank/data/zion
tank/data/zion/home

If tank/data/zion were added to a zone, each dataset would have the following properties.

Note that every parent of tank/zone/zion is visible as read-only, all descendents are writable, and datasets that are not part of the parent hierarchy are not visible at all. The zone administrator cannot change the sharenfs property because non-global zones cannot act as NFS servers. The zone administrator cannot change the zoned property because doing so would expose a security risk as described in the next section.

Privileged users in the zone can change any other settable property, except for quota and reservation properties. This behavior allows the global zone administrator to control the disk space consumption of all datasets used by the non-global zone.

In addition, the sharenfs and mountpoint properties cannot be changed by the global zone administrator after a dataset has been delegated to a non-global zone.

Understanding the zoned Property

When a dataset is delegated to a non-global zone, the dataset must be specially marked so that certain properties are not interpreted within the context of the global zone. After a dataset has been delegated to a non-global zone and is under the control of a zone administrator, its contents can no longer be trusted. As with any file system, there might be setuid binaries, symbolic links, or otherwise questionable contents that might adversely affect the security of the global zone. In addition, the mountpoint property cannot be interpreted in the context of the global zone. Otherwise, the zone administrator could affect the global zone's namespace. To address the latter, ZFS uses the zoned property to indicate that a dataset has been delegated to a non-global zone at one point in time.

The zoned property is a boolean value that is automatically turned on when a zone containing a ZFS dataset is first booted. A zone administrator does not need to manually turn on this property. If the zoned property is set, the dataset cannot be mounted or shared in the global zone. In the following example, tank/zone/zion has been delegated to a zone, while tank/zone/global has not:

# zfs list -o name,zoned,mountpoint -r tank/zone
NAME                  ZONED  MOUNTPOINT
tank/zone/global        off  /tank/zone/global
tank/zone/zion           on  /tank/zone/zion
# zfs mount
tank/zone/global           /tank/zone/global
tank/zone/zion             /export/zone/zion/root/tank/zone/zion

Note the difference between the mountpoint property and the directory where the tank/zone/zion dataset is currently mounted. The mountpoint property reflects the property as it is stored on disk, not where the dataset is currently mounted on the system.

When a dataset is removed from a zone or a zone is destroyed, the zoned property is not automatically cleared. This behavior is due to the inherent security risks associated with these tasks. Because an untrusted user has had complete access to the dataset and its descendents, the mountpoint property might be set to bad values, or setuid binaries might exist on the file systems.

To prevent accidental security risks, the zoned property must be manually cleared by the global zone administrator if you want to reuse the dataset in any way. Before setting the zoned property to off, ensure that the mountpoint property for the dataset and all its descendents are set to reasonable values and that no setuid binaries exist, or turn off the setuid property.

After you have verified that no security vulnerabilities are left, the zoned property can be turned off by using the zfs set or zfs inherit command. If the zoned property is turned off while a dataset is in use within a zone, the system might behave in unpredictable ways. Only change the property if you are sure the dataset is no longer in use by a non-global zone.