Managing ZFS Properties
Dataset properties are managed through the zfs command's set, inherit, and get subcommands.
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 the 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 and a dataset name.
The following example sets the atime property to off for tank/home. Only one property can be set or modified during each zfs set invocation.
# zfs set atime=off tank/home |
In addition, any file system property can be set when the file system is created. For example:
# zfs create -o atime=off tank/home |
You can specify numeric properties by using the following easy to understand suffixes (in 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 indicating that the quota property be set to the value of 50 Gbytes 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 |
Values of non-numeric properties are case-sensitive and must be lowercase, 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 their parent, unless a quota or reservation is explicitly set on the child. 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 setting, thus causing the setting to be inherited from the parent.
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 unset the compression property, thus causing the property to inherit the default setting of off. Because neither home nor tank have the compression property set locally, the default value is used. If both had compression on, 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 |
Note –
Be aware that the use of the -r option clears the current property setting for all descendent datasets.
For more information about the zfs 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 on a dataset:
# zfs get checksum tank/ws NAME PROPERTY VALUE SOURCE tank/ws checksum on default |
The fourth column, SOURCE, indicates where this property value has been set. The following table defines the meaning of the possible source values.
Table 6–3 Possible SOURCE Values (zfs get)|
Source Value |
Description |
|---|---|
|
default |
This property was never explicitly set for this dataset or any of its ancestors. The default value for this property is being used. |
|
inherited from dataset-name |
This property value is being inherited from the parent as specified by dataset-name. |
|
local |
This property value was explicitly set for this dataset by using zfs set. |
|
temporary |
This property value was set by using the zfs mount -o option and is only valid for the lifetime of the mount. For more information about temporary mount point properties, see Using Temporary Mount Properties. |
|
- (none) |
This property is a read-only property. Its value is generated by ZFS. |
You can use the special keyword all to retrieve all dataset properties. The following examples use the all keyword to retrieve all existing dataset properties:
# zfs get all tank NAME PROPERTY VALUE SOURCE tank type filesystem - tank creation Wed Nov 18 9:43 2009 - tank used 72K - tank available 66.9G - tank referenced 21K - 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 aclmode groupmask default tank aclinherit restricted default tank canmount on default tank shareiscsi off default tank xattr on default tank copies 1 default tank version 4 - 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 21K - tank usedbychildren 51K - tank usedbyrefreservation 0 - tank logbias latency default tank dedup off default tank mlslabel none 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 |
A recent feature enables you to make queries with the zfs get command without specifying a target file system, which means it 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. The -H option indicates that any header information should be omitted and that all white space be replaced with a tab. 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 Mbyte 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 above options to recursively retrieve the requested values for all descendents. The following example uses the -r, -o, and -H options to retrieve the dataset name and the value of the used property for export/home and its descendents, while omitting any 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 |
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