Creating a ZFS File System Hierarchy

After creating a storage pool to store your data, you can create your file system hierarchy. Hierarchies are simple yet powerful mechanisms for organizing information. They are also very familiar to anyone who has used a file system.

ZFS allows file systems to be organized into arbitrary hierarchies, where each file system has only a single parent. The root of the hierarchy is always the pool name. ZFS leverages this hierarchy by supporting property inheritance so that common properties can be set quickly and easily on entire trees of file systems.

How to Determine Your ZFS File System Hierarchy

1. Pick the file system granularity.

   ZFS file systems are the central point of administration. They are lightweight and can be created easily. A good model to use is a file system per user or project, as this model allows properties, snapshots, and backups to be controlled on a per-user or per-project basis.

   Two ZFS file systems, bonwick and billm, are created in How to Create ZFS File Systems.

   For more information on managing file systems, see Chapter 5, Managing ZFS File Systems.

2. Group similar file systems.

   ZFS allows file systems to be organized into hierarchies so that similar file systems can be grouped. This model provides a central point of administration for controlling properties and administering file systems. Similar file systems should be created under a common name.

   For the example in How to Create ZFS File Systems, the two file systems are placed under a file system named home.

3. Choose the file system properties.

   Most file system characteristics are controlled by using simple properties. These properties control a variety of behavior, including where the file systems are mounted, how they are shared, if they use compression, and if any quotas are in effect.

   For the example in How to Create ZFS File Systems, all home directories are mounted at /export/zfs/user, are shared by using NFS, and with compression enabled. In addition, a quota of 10 Gbytes on bonwick is enforced.

   For more information about properties, see Introducing ZFS Properties.

How to Create ZFS File Systems

1. Become root or assume an equivalent role with the appropriate ZFS rights profile.

   For more information about the ZFS rights profiles, see ZFS Rights Profiles.

2. Create the desired hierarchy.

   In this example, a file system that acts as a container for individual file systems is created.

   # zfs create tank/home

   Next, individual file systems are grouped under the home file system in the pool tank.

3. Set the inherited properties.

   After the file system hierarchy is established, set up any properties that should be shared among all users:

   # zfs set mountpoint=/export/zfs tank/home
   # zfs set sharenfs=on tank/home
   # zfs set compression=on tank/home
   # zfs get compression tank/home
   NAME             PROPERTY       VALUE                      SOURCE
   tank/home        compression    on                         local

   A new feature is available that enables you to set file system properties when the file system is created. For example:

   # zfs create -o mountpoint=/export/zfs -o sharenfs=on -o compression=on tank/home

   For more information about properties and property inheritance, see Introducing ZFS Properties.

4. Create the individual file systems.

   Note that the file systems could have been created and then the properties could have been changed at the home level. All properties can be changed dynamically while file systems are in use.

   # zfs create tank/home/bonwick
   # zfs create tank/home/billm

   These file systems inherit their property settings from their parent, so they are automatically mounted at /export/zfs/user and are NFS shared. You do not need to edit the /etc/vfstab or /etc/dfs/dfstab file.

   For more information about creating file systems, see Creating a ZFS File System.

   For more information about mounting and sharing file systems, see Mounting and Sharing ZFS File Systems.

5. Set the file system-specific properties.

   In this example, user bonwick is assigned a quota of 10 Gbytes. This property places a limit on the amount of space he can consume, regardless of how much space is available in the pool.

   # zfs set quota=10G tank/home/bonwick

6. View the results.

   View available file system information by using the zfs list command:

   # zfs list
   NAME                   USED  AVAIL  REFER  MOUNTPOINT
   tank                  92.0K  67.0G   9.5K  /tank
   tank/home             24.0K  67.0G     8K  /export/zfs
   tank/home/billm          8K  67.0G     8K  /export/zfs/billm
   tank/home/bonwick        8K  10.0G     8K  /export/zfs/bonwick

   Note that the user bonwick only has 10 Gbytes of space available, while the user billm can use the full pool (67 Gbytes).

   For more information about viewing file system status, see Querying ZFS File System Information.

   For more information about how space is used and calculated, see ZFS Space Accounting.