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Solaris ZFS Administration Guide
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Using ZFS on a Solaris System With Zones Installed

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

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

  • You can add a ZFS file system or a ZFS clone to a non-global 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

  • Do not use a ZFS file system for a global zone root path or a non-global zone root path in the Solaris 10 releases. You can use ZFS as a zone root path in the Solaris Express releases, but keep in mind that patching or upgrading these zones is not supported.

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

Adding a dataset allows the non-global zone to share space with the global zone, though the zone administrator cannot control properties or create new file systems in the underlying file system hierarchy. This 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 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, and modify properties of the datasets. The zone administrator cannot affect datasets that have not been added to the zone, and cannot exceed any top-level quotas set on the exported dataset.

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

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

  • When a source zonepath and the target zonepath both reside on ZFS and are in the same pool, zoneadm clone will now automatically use ZFS clone to clone a zone. The zoneadm clone command will take 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, Zones, in System Administration Guide: Virtualization Using the Solaris Operating System.

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.

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

In the following example, a ZFS file system is added to a non-global zone by a global administrator in 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, 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, Zones, in System Administration Guide: Virtualization Using the Solaris Operating System.

Delegating Datasets to a Non-Global Zone

If the primary goal is to delegate the administration of storage to a zone, then ZFS supports adding datasets to a non-global zone through 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 administrator in 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 children. In addition, the zone administrator can take snapshots, create clones, and otherwise control the entire file system hierarchy.

For more information about what actions are allowed within zones, see Managing ZFS Properties Within a Zone.

Adding ZFS Volumes to a Non-Global Zone

ZFS volumes cannot be added to a non-global zone by using the zonecfg command's add dataset subcommand. If an attempt to add an ZFS volume is detected, the zone cannot boot. However, volumes can be added to a zone by using the zonecfg command's add device subcommand.

In the following example, a ZFS volume is added to a non-global zone by a global administrator in the global zone:

# zonecfg -z zion
zion: No such zone configured
Use 'create' to begin configuring a new zone.
zonecfg:zion> create
zonecfg:zion> add device
zonecfg:zion:device> set match=/dev/zvol/dsk/tank/vol
zonecfg:zion:device> end

This syntax exports the tank/vol volume to the zone. Note that adding a raw volume to a zone has implicit security risks, even if the volume doesn't correspond to a physical device. In particular, the zone administrator could create malformed file systems that would panic the system when a mount is attempted. For more information about adding devices to zones and the related security risks, see Understanding the zoned Property.

For more information about adding devices to zones, see Part II, Zones, in System Administration Guide: Virtualization Using the Solaris Operating System.

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. While 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 added to a zone, the zone administrator can control specific dataset properties. When a dataset is added to a zone, all its ancestors are visible as read-only datasets, while the dataset itself is writable as are all of its children. 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 is added to a zone, each dataset would have the following properties.

Dataset

Visible

Writable

Immutable Properties

tank

Yes

No

-

tank/home

No

-

-

tank/data

Yes

No

-

tank/data/matrix

No

-

-

tank/data/zion

Yes

Yes

sharenfs, zoned, quota, reservation

tank/data/zion/home

Yes

Yes

sharenfs, zoned

Note that every parent of tank/zone/zion is visible read-only, all children 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. Neither can the zone administrator change the zoned property, because doing so would expose a security risk as described in the next section.

Any other settable property can be changed, except for the quota property, and the dataset itself. This behavior allows the global zone administrator to control the 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 once a dataset has been added to a non-global zone.

Understanding the zoned Property

When a dataset is added 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 added to a non-global zone 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 will 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, and is ignored when the zfs share -a command or the zfs mount -a command is executed. In the following example, tank/zone/zion has been added 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 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 children, 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 administrator if you want to reuse the dataset in any way. Before setting the zoned property to off, make sure that the mountpoint property for the dataset and all its children 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 commands. 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.

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  Published under the terms fo the Public Documentation License Version 1.01. Design by Interspire