Managing ZFS Properties

Dataset properties are managed through the zfs command's set, inherit, and get subcommands.

• Setting ZFS Properties

• Inheriting ZFS Properties

• Querying ZFS Properties

Setting ZFS Properties

You can use the zfs set command to modify any settable dataset property. Or, you can use the zfs create command to set properties when a dataset is created. For a list of settable dataset properties, see Settable ZFS Native Properties.

The zfs set command takes a property/value sequence in the format of property=value followed by a dataset name. Only one property can be set or modified during each zfs set invocation.

The following example sets the atime property to off for tank/home.

# zfs set atime=off tank/home

In addition, any file system property can be set when a file system is created. For example:

# zfs create -o atime=off tank/home

You can specify numeric property values by using the following easy-to-understand suffixes (in increasing order of magnitude): BKMGTPEZ. Any of these suffixes can be followed by an optional b, indicating bytes, with the exception of the B suffix, which already indicates bytes. The following four invocations of zfs set are equivalent numeric expressions that set the quota property be set to the value of 50 GB on the tank/home/marks file system:

# zfs set quota=50G tank/home/marks
# zfs set quota=50g tank/home/marks
# zfs set quota=50GB tank/home/marks
# zfs set quota=50gb tank/home/marks

The values of non-numeric properties are case-sensitive and must be in lowercase letters, with the exception of mountpoint and sharenfs. The values of these properties can have mixed upper and lower case letters.

For more information about the zfs set command, see zfs(1M).

Inheriting ZFS Properties

All settable properties, with the exception of quotas and reservations, inherit their value from the parent dataset, unless a quota or reservation is explicitly set on the descendent dataset. If no ancestor has an explicit value set for an inherited property, the default value for the property is used. You can use the zfs inherit command to clear a property value, thus causing the value to be inherited from the parent dataset.

The following example uses the zfs set command to turn on compression for the tank/home/bonwick file system. Then, zfs inherit is used to clear the compression property, thus causing the property to inherit the default value of off. Because neither home nor tank has the compression property set locally, the default value is used. If both had compression enabled, the value set in the most immediate ancestor would be used (home in this example).

# zfs set compression=on tank/home/bonwick
# zfs get -r compression tank
NAME             PROPERTY      VALUE                    SOURCE
tank             compression   off                      default
tank/home        compression   off                      default
tank/home/bonwick compression   on                      local
# zfs inherit compression tank/home/bonwick
# zfs get -r compression tank
NAME             PROPERTY      VALUE                    SOURCE
tank             compression   off                      default
tank/home        compression   off                      default
tank/home/bonwick compression  off                      default

The inherit subcommand is applied recursively when the -r option is specified. In the following example, the command causes the value for the compression property to be inherited by tank/home and any descendents it might have:

# zfs inherit -r compression tank/home

For more information about the zfs inherit command, see zfs(1M).

Querying ZFS Properties

The simplest way to query property values is by using the zfs list command. For more information, see Listing Basic ZFS Information. However, for complicated queries and for scripting, use the zfs get command to provide more detailed information in a customized format.

You can use the zfs get command to retrieve any dataset property. The following example shows how to retrieve a single property value on a dataset:

# zfs get checksum tank/ws
NAME             PROPERTY       VALUE                      SOURCE
tank/ws          checksum       on                         default

The fourth column, SOURCE, indicates the origin of this property value. The following table defines the possible source values.

Table 6-3 Possible SOURCE Values (zfs get Command)

You can use the special keyword all to retrieve all dataset property values. The following examples use the all keyword:

# zfs get all tank
NAME  PROPERTY              VALUE                  SOURCE
tank  type                  filesystem             -
tank  creation              Fri Oct  8 16:47 2010  -
tank  used                  1.31M                  -
tank  available             66.9G                  -
tank  referenced            35K                    -
tank  compressratio         1.00x                  -
tank  mounted               yes                    -
tank  quota                 none                   default
tank  reservation           none                   default
tank  recordsize            128K                   default
tank  mountpoint            /tank                  default
tank  sharenfs              off                    default
tank  checksum              on                     default
tank  compression           off                    default
tank  atime                 on                     default
tank  devices               on                     default
tank  exec                  on                     default
tank  setuid                on                     default
tank  readonly              off                    default
tank  zoned                 off                    default
tank  snapdir               hidden                 default
tank  aclinherit            restricted             default
tank  canmount              on                     default
tank  xattr                 on                     default
tank  copies                1                      default
tank  version               5                      -
tank  utf8only              off                    -
tank  normalization         none                   -
tank  casesensitivity       sensitive              -
tank  vscan                 off                    default
tank  nbmand                off                    default
tank  sharesmb              off                    default
tank  refquota              none                   default
tank  refreservation        none                   default
tank  primarycache          all                    default
tank  secondarycache        all                    default
tank  usedbysnapshots       0                      -
tank  usedbydataset         35K                    -
tank  usedbychildren        1.27M                  -
tank  usedbyrefreservation  0                      -
tank  logbias               latency                default
tank  dedup                 off                    default
tank  mlslabel              none                   default
tank  sync                  standard               default
tank  encryption            off                    -
tank  keysource             none                   default
tank  keystatus             none                   -
tank  rekeydate             -                      default

The -s option to zfs get enables you to specify, by source type, the properties to display. This option takes a comma-separated list indicating the desired source types. Only properties with the specified source type are displayed. The valid source types are local, default, inherited, temporary, and none. The following example shows all properties that have been locally set on pool.

# zfs get -s local all pool
NAME             PROPERTY      VALUE                      SOURCE
pool             compression   on                         local

Any of the above options can be combined with the -r option to recursively display the specified properties on all children of the specified dataset. In the following example, all temporary properties on all datasets within tank are recursively displayed:

# zfs get -r -s temporary all tank
NAME             PROPERTY       VALUE                      SOURCE
tank/home          atime          off                      temporary
tank/home/bonwick  atime          off                      temporary
tank/home/marks    atime          off                      temporary

You can query property values by using the zfs get command without specifying a target file system, which means the command operates on all pools or file systems. For example:

# zfs get -s local all
tank/home               atime          off                    local
tank/home/bonwick       atime          off                    local
tank/home/marks         quota          50G                    local

For more information about the zfs get command, see zfs(1M).

Querying ZFS Properties for Scripting

The zfs get command supports the -H and -o options, which are designed for scripting. You can use the -H option to omit header information and to replace white space with the Tab character. Uniform white space allows for easily parseable data. You can use the -o option to customize the output in the following ways:

• The literal name can be used with a comma-separated list of properties as defined in the Introducing ZFS Properties section.

• A comma-separated list of literal fields, name, value, property, and source, to be output followed by a space and an argument, which is a comma-separated list of properties.

The following example shows how to retrieve a single value by using the -H and -o options of zfs get:

# zfs get -H -o value compression tank/home
on

The -p option reports numeric values as their exact values. For example, 1 MB would be reported as 1000000. This option can be used as follows:

# zfs get -H -o value -p used tank/home
182983742

You can use the -r option, along with any of the preceding options, to recursively retrieve the requested values for all descendents. The following example uses the -H, -o, and -r options to retrieve the dataset name and the value of the used property for export/home and its descendents, while omitting the header output:

# zfs get -H -o name,value -r used export/home
export/home             5.57G
export/home/marks       1.43G
export/home/maybee      2.15G