ZFS Volumes

A ZFS volume is a dataset that represents a block device. ZFS volumes are identified as devices in the /dev/zvol/{dsk,rdsk}/pool directory.

In the following example, a 5-GB ZFS volume, tank/vol, is created:

# zfs create -V 5gb tank/vol

When you create a volume, a reservation is automatically set to the initial size of the volume so that unexpected behavior doesn't occur. For example, if the size of the volume shrinks, data corruption might occur. You must be careful when changing the size of the volume.

In addition, if you create a snapshot of a volume that changes in size, you might introduce inconsistencies if you attempt to roll back the snapshot or create a clone from the snapshot.

For information about file system properties that can be applied to volumes, see Table 5-1.

You can display a ZFS volume's property information by using the zfs get or zfs get all command. For example:

# zfs get all tank/vol

A question mark (?) displayed for volsize in the zfs get output indicates an unknown value because an I/O error occurred. For example:

# zfs get -H volsize tank/vol
tank/vol        volsize ?       local 

An I/O error generally indicates a problem with a pool device. For information about resolving pool device problems, see Resolving Problems With ZFS.

If you are using a Solaris system with zones installed, you cannot create or clone a ZFS volume in a non-global zone. Any attempt to do so will fail. For information about using ZFS volumes in a global zone, see Adding ZFS Volumes to a Non-Global Zone.

Using a ZFS Volume as a Swap or Dump Device

During installation of a ZFS root file system or a migration from a UFS root file system, a swap device is created on a ZFS volume in the ZFS root pool. For example:

# swap -l
swapfile                  dev    swaplo   blocks     free
/dev/zvol/dsk/rpool/swap 253,3        16  8257520  8257520

During installation of a ZFS root file system or a migration from a UFS root file system, a dump device is created on a ZFS volume in the ZFS root pool. The dump device requires no administration after it is set up. For example:

# dumpadm
      Dump content: kernel pages
       Dump device: /dev/zvol/dsk/rpool/dump (dedicated)
Savecore directory: /var/crash/
  Savecore enabled: yes

If you need to change your swap area or dump device after the system is installed, use the swap and dumpadm commands as in previous Solaris releases. If you need to create an additional swap volume, create a ZFS volume of a specific size and then enable swap on that device. Then, add an entry for the new swap device in the /etc/vfstab file. For example:

# zfs create -V 2G rpool/swap2
# swap -a /dev/zvol/dsk/rpool/swap2
# swap -l
swapfile                   dev  swaplo blocks   free
/dev/zvol/dsk/rpool/swap  256,1      16 2097136 2097136
/dev/zvol/dsk/rpool/swap2 256,5      16 4194288 4194288

Do not swap to a file on a ZFS file system. A ZFS swap file configuration is not supported.

For information about adjusting the size of the swap and dump volumes, see Adjusting the Sizes of Your ZFS Swap and Dump Devices.

Using a ZFS Volume as an iSCSI LUN

The Common Multiprotocol SCSI Target (COMSTAR) software framework enables you to convert any Oracle Solaris host into a SCSI target device that can be accessed over a storage network by initiator hosts. You can create and configure a ZFS volume to be shared as an iSCSI logical unit (LUN).

First, install the COMSTAR package.

# pkg install group/feature/storage-server

Next, create a ZFS volume to be used as an iSCSI target and then create the SCSI-block-device-based LUN. For example:

# zfs create -V 2g tank/volumes/v2
# sbdadm create-lu /dev/zvol/rdsk/tank/volumes/v2
Created the following LU:

              GUID                    DATA SIZE           SOURCE
--------------------------------  -------------------  ----------------
600144f000144f1dafaa4c0faff20001  2147483648           /dev/zvol/rdsk/tank/volumes/v2
# sbdadm list-lu
Found 1 LU(s)

              GUID                    DATA SIZE           SOURCE
--------------------------------  -------------------  ----------------
600144f000144f1dafaa4c0faff20001  2147483648           /dev/zvol/rdsk/tank/volumes/v2

You can expose the LUN views to all clients or selected clients. Identify the LUN GUID and then share the LUN view. In the following example, the LUN view is shared to all clients.

# stmfadm list-lu
LU Name: 600144F000144F1DAFAA4C0FAFF20001
# stmfadm add-view 600144F000144F1DAFAA4C0FAFF20001
# stmfadm list-view -l 600144F000144F1DAFAA4C0FAFF20001
View Entry: 0
    Host group   : All
    Target group : All
    LUN          : 0

The next step is to create the iSCSI targets. For information about creating the iSCSI targets, see Chapter 11, Configuring Storage Devices With COMSTAR (Tasks), in Oracle Solaris 11.1 Administration: Devices and File Systems.

A ZFS volume as an iSCSI target is managed just like any other ZFS dataset, except that you cannot rename the dataset, roll back a volume snapshot, or export the pool while the ZFS volumes are shared as iSCSI LUNs. You will see messages similar to the following:

# zfs rename tank/volumes/v2 tank/volumes/v1
cannot rename 'tank/volumes/v2': dataset is busy
# zpool export tank
cannot export 'tank': pool is busy

All iSCSI target configuration information is stored within the dataset. Like an NFS shared file system, an iSCSI target that is imported on a different system is shared appropriately.