5.2.1 Read-Only Properties
Read-only properties are properties that can be retrieved but cannot be set.
Read-only properties are not inherited. Some properties are specific to a particular
type of dataset; in such cases the particular dataset type is called out in the description.
available -- The amount of space available
to the dataset and all its children, assuming no other activity in the pool. Because
space is shared within a pool, this can be limited by any number of factors, including
physical pool size, quotas, reservations, or other datasets within the pool.
This property can also be referred to by its shortened column name, avail.
For more information about space accounting, see 3.2 Space Accounting.
This property can also be
referred to by its shortened column name, avail.
creation -- Date and time that this dataset
was created.
mounted -- Indicates whether this filesystem,
clone, or snapshot is currently mounted; does not apply to volumes.
origin -- For cloned filesystems only; the
snapshot from which this clone originated. Non-cloned filesystems have an origin of
none. The origin cannot be destroyed so long as a clone exists.
compressratio -- The compression ratio achieved
on this dataset. Calculated from the logical size of all files and the amount of referenced
physical data. Includes explicit savings through the use of the compression property.
referenced -- The amount of data accessible
by this dataset, which may or may not be shared with other datasets in the pool. When
a snapshot or clone is created, it initially references the same amount of space as
the file system or snapshot it was created from, since its contents are identical.
This property can also be referred to by its shortened column name, refer.
type -- Dataset type such as filesystem (filesystem/clone), volume, or snapshot
used -- The amount of space consumed by
this dataset and all its descendants. This is the value that is checked against this
dataset's quota and reservation. The space used does not include this dataset's reservation,
but does take into account the reservations of any descendant datasets. The amount
of space that a dataset consumes from its parent, as well as the amount of space that
is freed if this dataset is recursively destroyed, is the greater of its space used
and its reservation.
When snapshots are created, their space is initially
shared between the snapshot and the file system, and possibly with previous snapshots.
As the file system changes, space that was previously shared becomes unique to the
snapshot, and counted in the snapshot's space used. Additionally, deleting snapshots
can increase the amount of space unique to (and used by) other snapshots. For more
information about snapshots and space issues, see 3.3 Out of Space Behavior.
The amount of space used, available, or referenced
does not take into account pending changes. Pending changes are generally accounted
for within a few seconds. Committing a change to a disk using fsync(3c) or O_SYNC does not necessarily guarantee that the space usage information will
be updated immediately.
For more information on space accounting: including the used, referenced, and available properties listed above
see 3.2 Space Accounting.
5.2.2 Settable Properties
Settable properties are properties whose values can be both retrieved and set.
Settable properties are set via the zfs set interface described
in 5.4.1 Setting Properties. With the exceptions of quotas
and reservations, settable properties are inherited. For more information on quotas
and reservations, see 5.6 Quotas and Reservations.
Some settable properties are specific to a particular type of dataset; in such
cases the particular dataset type is called out in the description field of the table.
If not specifically mentioned, a property applies to all dataset types: filesystems,
volumes, clones, and snapshots.
atime -- Controls whether the access time
for files is updated when read. Turning this property off avoids producing write traffic
when reading files and can result in significant performance gains, though it may
confuse mailers and other similar utilities.
checksum -- Controls the checksum used to
verify data integrity. The value on automatically selects an appropriate
algorithm (currently fletcher2, but this may change in future releases).
The value off disables integrity checking on user data; this is not recommended.
compression -- Controls the compression
algorithm used for this dataset. The value on automatically selects
an appropriate algorithm. There is currently only one algorithm, lzjb,
though this may change in future releases.
devices -- Controls whether device nodes
found within this filesystem can be opened.
exec -- Controls whether programs within
this filesystem are allowed to be executed. Also, when set to off, mmap(2) calls with PROT_EXEC will be disallowed.
mountpoint -- Controls the mount point
used for this filesystem. When the mountpoint property is changed
for a filesystem, the filesystem and any children that inherit the mount point are
unmounted. If the new value is legacy, then they remain unmounted.
Otherwise, they are automatically remounted in the new location if the property was
previously legacy or none, or if they were mounted
before the property was changed. In addition, any shared file systems are unshared
and shared in the new location.
For more information on using this property,
see 5.5.1 Managing Mount Points.
quota -- Limits the amount of space a dataset
and its descendents can consume. This enforces a hard limit on the amount of space
used. This includes all space consumed by descendents, including file systems and
snapshots. Setting a quota on a descendent of a dataset that already has a quota does
not override the ancestor's quota, but rather imposes an additional limit. Quotas
cannot be set on volumes, as the volsize property acts as an
implicit quota.
For information about setting quotas, see 5.6.1 Setting Quotas.
readonly -- Controls whether this dataset
can be modified. When set to on, no modifications can be made to
the dataset.
recordsize -- Specifies a suggested block
size for files in the file system. This property is designed solely for use with database
workloads that access files in fixed-size records. ZFS automatically tunes block sizes
according to internal algorithms optimized for typical access patterns. For databases
that create very large files but access them in small random chunks, these algorithms
may be suboptimal. Specifying a recordsize greater than or equal
to the record size of the database can result in significant performance gains. Use
of this property for general purpose file systems is strongly discouraged, and may
adversely affect performance. The size specified must be a power of two greater than
or equal to 512 and less than or equal to 128 Kbytes. Changing the filesystem's recordsize only affects files created afterward; existing files are unaffected.
This property can also be referred to by its shortened column name, recsize.
reservation -- The minimum amount of space
guaranteed to a dataset and its descendents. When the amount of space used is below
this value, the dataset is treated as if it were taking up the amount of space specified
by its reservation. Reservations are accounted for in the parent datasets' space used,
and count against the parent datasets' quotas and reservations. This property can
also be referred to by its shortened column name, reserv.
For more information, see 5.6.2 Setting Reservations).
sharenfs -- Controls whether the filesystem
is shared via NFS, and what options are used. A filesystem with a sharenfs property of off is managed through traditional tools
such as share(1M), unshare(1M), and dfstab(4). Otherwise, the filesystem is automatically
shared and unshared with the zfs share and zfs unshare commands. If the property is set to on, the share(1M)
command is invoked with no options. Otherwise, the share(1M) command is invoked with
options equivalent to the contents of this property. When the sharenfs property is changed for a dataset, the dataset and any children are re-shared
with the new options, only if the property was previously off,
or if they were shared before the property was changed. If the new property is off, the filesystems are unshared.
For more information on sharing
ZFS filesystems, see 5.5.5 Sharing ZFS File Systems.
setuid -- Controls whether the set-UID bit
is respected for the filesystem.
snapdir -- Controls whether the .zfs directory is hidden or visible in the root of the file system. For
more information on using snapshots, see 6.1 ZFS Snapshots.
volsize -- The logical size of the volume.
By default, creating a volume establishes a reservation for the same amount. Any changes
to volsize are reflected in an equivalent change to the reservation.
These checks are used to prevent unexpected behavior for consumers. A volume which
contains less space than it claims is available can result in undefined behavior or
data corruption, depending on how the volume is used. These effects can also occur
when the volume size is changed while it is in use (particularly when shrinking the
size). Extreme care should be used when adjusting the volume size.
Though
not recommended, you can create a sparse volume by specifying
the -s flag to zfs create -V, or by changing the
reservation once the volume has been created. A sparse volume is defined as a volume
where the reservation is not equal to the volume size. For a sparse volume, changes
to volsize are not reflected in the reservation.
For more information about using volumes, see 8.1 Emulated Volumes.
volblocksize -- For volumes, specifies
the block size of the volume. The blocksize cannot be changed once the volume has
been written, so it should be set at volume creation time. The default blocksize for
volumes is 8 Kbytes. Any power of 2 from 512 bytes to 128 Kbytes is valid.
This property can also be referred to by its shortened column name, volblock.
zoned -- Indicates whether this dataset
has been added to a non-global zone. If this is set, then the mount point is not respected
in the global zone, and ZFS refuses to mount such a filesystem when asked. When a
zone is first installed, this is set for any added filesystems. For more information
on using ZFS with zones installed, see 8.2 Using ZFS on a Solaris System With Zones Installed.
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