Introducing ZFS Properties
Properties are the main mechanism that you use to control the behavior of file
systems, volumes, snapshots, and clones. Unless stated otherwise, the properties defined
in this section apply to all the dataset types.
Properties are divided into two types, native properties and user-defined properties.
Native properties either provide internal statistics or control ZFS file system
behavior. In addition, native properties are either settable or read-only. User
properties have no effect on ZFS file system behavior, but you can use them to annotate
datasets in a way that is meaningful in your environment. For more information about
user properties, see ZFS User Properties.
Most settable properties are also inheritable. An inheritable property is a property
that, when set on a parent file system, is propagated down to all of its
descendents.
All inheritable properties have an associated source that indicates how a
property was obtained. The source of a property can have the following values:
- local
-
Indicates that the property was explicitly set on the dataset by using the
zfs set command as described in Setting ZFS Properties.
- inherited from
dataset-name
-
Indicates that the property was inherited from the named ancestor.
- default
-
Indicates that the property value was not inherited or set locally. This
source is a result of no ancestor having the property set as source
local.
The following table identifies both read-only and settable native ZFS file system
properties. Read-only native properties are identified as such. All other native
properties listed in this table are settable. For information about user properties, see
ZFS User Properties.
Table 3 ZFS Native Property Descriptions
|
|
|
|
|
aclinherit
|
String
|
secure
|
|
|
aclmode
|
String
|
groupmask
|
|
|
atime
|
Boolean
|
on
|
Controls whether the access time for files is updated
when they are read. Turning this property off avoids producing write
traffic when reading files and can result in significant performance
gains, though it might confuse mailers and similar utilities.
|
|
available
|
Number
|
N/A
|
Read-only property that identifies the amount of disk
space available to a file system and all its children, assuming no
other activity in the pool. Because disk space is shared within a
pool, available space can be limited by various factors including
physical pool size, quotas, reservations, and other datasets within
the pool. The property abbreviation is avail.
|
|
canmount
|
Boolean
|
on
|
Controls whether a file system can be mounted with the
zfs
mount command. This property can be set on any
file system, and the property itself is not inheritable. However,
when this property is set to off, a mount point
can be inherited to descendent file systems, but the file system
itself is never mounted.
When the noauto option is set, a file system
can only be mounted and unmounted explicitly. The file system is not
mounted automatically when the file system is created or imported,
nor is it mounted by the zfs
mount–a command or unmounted by the
zfs unmount–a command.
|
|
casesensitivity
|
String
|
mixed
|
This property indicates whether the file name matching algorithm
used by the file system should be casesensitive,
caseinsensitive, or allow a combination of
both styles of matching (mixed). Traditionally,
UNIX and POSIX file systems have case-sensitive file names.
The mixed value for this property indicates the
file system can support requests for both case-sensitive and
case-insensitive matching behavior. Currently, case-insensitive
matching behavior on a file system that supports mixed behavior is
limited to the Oracle Solaris SMB server product. For more information about
using the mixed value, see The casesensitivity Property.
Regardless of the casesensitivity
property setting, the file system preserves the case of the name
specified to create a file. This property cannot be changed after
the file system is created. |
|
checksum
|
String
|
on
|
Controls the checksum used to verify data integrity. The
default value is on, which automatically selects
an appropriate algorithm, currently fletcher4.
The values are on, off, fletcher2, fletcher4,
sha256, and sha256+mac. A value of
off disables integrity checking on user data.
A value of off is not recommended. |
|
compression
|
String
|
off
|
Enables or disables compression for a dataset. The
values are on, off,
lzjb, lz4,
gzip, and
gzip-N. Currently,
setting this property to lzjb,
gzip, or
gzip-N has the
same effect as setting this property to on.
Enabling compression on a file system with existing data only
compresses new data. Existing data remains uncompressed. The property abbreviation is compress.
|
|
compressratio
|
Number
|
N/A
|
Read-only property that identifies the compression ratio
achieved for a dataset, expressed as a multiplier. Compression can
be enabled by the zfs set compression=on
dataset command. The value is calculated from the logical size of all files and the
amount of referenced physical data. It includes explicit savings
through the use of the compression
property.
|
|
copies
|
Number
|
1
|
Sets the number of copies of user data per file system.
Available values are 1, 2, or
3. These copies are in addition to any
pool-level redundancy. Disk space used by multiple copies of user
data is charged to the corresponding file and dataset, and counts
against quotas and reservations. In addition, the
used property is updated when multiple copies
are enabled. Consider setting this property when the file system is
created because changing this property on an existing file system
only affects newly written data. |
|
creation
|
String
|
N/A
|
Read-only property that identifies the date and time
that a dataset was created. |
|
dedup
|
String
|
off
|
Controls the ability to remove duplicate data in a ZFS file
system. Possible values are on,
off, verify, and
sha256[,verify]. The default checksum for
deduplication is sha256.
|
|
defaultgroupquota
|
String
|
None
|
Sets a default group quota. The value applies to all
groups who do not have an explicit group quota specified. The
default value is none. For more information, see Setting Default User and Group Quotas. |
|
defaultuserquota
|
String
|
None
|
Sets a default user quota. The value applies to all
users who do not have an explicit user quota specified. The default
value is none. For more information, see Setting Default User and Group Quotas. |
|
devices
|
Boolean
|
on
|
Controls whether device files in a file system can be
opened. |
|
encryption
|
Boolean
|
off
|
Controls whether a file system is encrypted. An
encrypted file system means that data is encoded and a key is needed
by the file system owner to access the data. |
|
exec
|
Boolean
|
on
|
Controls whether programs in a file system are allowed
to be executed. Also, when set to off,
mmap(2) calls with
PROT_EXEC are disallowed. |
|
keychangedate
|
String
|
none
|
Read-only property that identifies the date of the last
wrapping key change from a zfs key
–c operation for the specified file system. If no
key change operation has occurred, the value of this property is the
same as the file system's creation date. |
|
keysource
|
String
|
none
|
Identifies the format and location of the key that wraps
the file system keys. The valid property values are
raw, hex,
passphrase,prompt, or
file. The key must be present when
the file system is created, mounted, or loaded by using the
zfs key
–l command. If encryption is enabled for a new file
system, the default keysource is
passphrase,prompt. |
|
keystatus
|
String
|
none
|
Read-only property that identifies the file system's
encryption key status. The availability of a file system's key is
indicated by available or
unavailable. For file systems that do not
have encryption enabled, none is
displayed. |
|
logbias
|
String
|
latency
|
Controls how ZFS optimizes synchronous requests for this
file system. If logbias is set to
latency, ZFS uses the pool's separate log
devices, if any, to handle the requests at low latency. If
logbias is set to
throughput, ZFS does not use the pool's
separate log devices. Instead, ZFS optimizes synchronous operations
for global pool throughput and efficient use of resources. The
default value is latency. |
|
mlslabel
|
String
|
None
|
See the multilevel property for a description
of the behavior of the mlslabel property on
multilevel file systems. The following mlslabel
description applies to non-multilevel file systems.
Provides a sensitivity label that determines if a file
system can be mounted in a zone. If the labeled file system matches
the labeled zone, the file system can be mounted and accessed from
the labeled zone. The default value is none. This
property can only be modified with the appropriate privilege. |
|
mounted
|
Boolean
|
N/A
|
Read-only property that indicates whether a file system,
clone, or snapshot is currently mounted. This property does not
apply to volumes. The value can be either yes or
no. |
|
mountpoint
|
String
|
N/A
|
Controls the mount point used for this file system. When
the mountpoint property is changed for a file
system, the file system and any descendents 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. |
|
multilevel
|
Boolean
|
off
|
Objects in a multilevel file system are individually
labeled with an explicit sensitivity label attribute that is
automatically generated. Objects can be relabeled in place by
changing this label attribute, by using the
setlabel or setflabel
interfaces. The default value is off. A root file system, an Oracle Solaris Zone file system, or a file system
that contains packaged Solaris code should not be multilevel.
There are differences in the mlslabel property
on a multilevel file system. The mlslabel value
defines the highest possible label for objects in the file system.
An attempt to create a file at (or relabel a file to) a label higher
than the mlslabel value is not allowed. Mount
policy based on the mlslabel value does not apply
to a multilevel file system.
For a multilevel file system, the mlslabel
property can be set explicitly when the file system is created.
Otherwise, a default mlslabel property of
ADMIN_HIGH is automatically created. After
creating a multilevel file system, the mlslabel
property can be changed, but it cannot be set to a lower label, set
to none, nor can it be removed.
|
|
nbmand
|
Boolean
|
off
|
Controls whether the file system should be mounted with
nbmand (Non-blocking mandatory) locks. This
property is for SMB clients only. Changes to this property only take
effect when the file system is unmounted and remounted. |
|
normalization
|
String
|
None
|
This property indicates whether a file system should
perform a unicode normalization of file names whenever two file
names are compared, and which normalization algorithm should be
used. File names are always stored unmodified, names are normalized
as part of any comparison process. If this property is set to a
legal value other than none, and the
utf8only property was left unspecified, the
utf8only property is automatically set to
on. The default value of the
normalization property is
none. This property cannot be changed after
the file system is created. |
|
origin
|
String
|
N/A
|
Read-only property for cloned file systems or volumes that
identifies the snapshot from which the clone was created. The origin
cannot be destroyed (even with the –r or
–f option) as long as a clone exists.
Non-cloned file systems have an origin of
none. |
|
primarycache
|
String
|
all
|
Controls what is cached in the primary cache (ARC).
Possible values are all, none,
and metadata. If set to all,
both user data and metadata are cached. If set to
none, neither user data nor metadata is
cached. If set to metadata, only metadata is
cached. When these properties are set on existing file systems, only
new I/O is cache based on the values of these properties. Some
database environments might benefit from not caching user data. You
must determine if setting cache properties is appropriate for your
environment. |
|
quota
|
Number (or none)
|
none
|
Limits the amount of disk space a file system and its
descendents can consume. This property enforces a hard limit on the
amount of disk space used, including all space consumed by
descendents, such as file systems and snapshots. Setting a quota on
a descendent of a file system 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. |
|
readonly
|
Boolean
|
off
|
Controls whether a dataset can be modified. When set to
on, no modifications can be made. The property abbreviation is rdonly.
|
|
recordsize
|
Number
|
128K
|
Specifies a suggested block size for files in a file
system. |
|
referenced
|
Number
|
N/A
|
Read-only property that identifies the amount of data
accessible by a dataset, which might or might not be shared with
other datasets in the pool. When a snapshot or clone is created, it initially references the
same amount of disk space as the file system or snapshot it was
created from, because its contents are identical.
The property abbreviation is refer.
|
|
refquota
|
Number (or none)
|
none
|
Sets the amount of disk space that a dataset can
consume. This property enforces a hard limit on the amount of space
used. This hard limit does not include disk space used by
descendents, such as snapshots and clones. |
|
refreservation
|
Number (or none)
|
none
|
Sets the minimum amount of disk space that is guaranteed
to a dataset, not including descendents, such as snapshots and
clones. When the amount of disk space used is below this value, the
dataset is treated as if it were taking up the amount of space
specified by refreservation. The
refreservation reservation is accounted for
in the parent dataset's disk space used, and counts against the
parent dataset's quotas and reservations. If refreservation is set, a snapshot is only
allowed if enough free pool space is available outside of this
reservation to accommodate the current number of
referenced bytes in the dataset.
The property abbreviation is refreserv.
|
|
rekeydate
|
String
|
N/A
|
Read-only property that indicates the date of the last
data encryption key change from a zfs key
–K or zfs clone
–K operation on this file system. If no
rekey operation has been performed, the value
of this property is the same as the creation
date. |
|
reservation
|
Number (or none)
|
none
|
Sets the minimum amount of disk space guaranteed to a
file system and its descendents. When the amount of disk space used
is below this value, the file system is treated as if it were using
the amount of space specified by its reservation. Reservations are
accounted for in the parent file system's disk space used, and count
against the parent file system's quotas and reservations. The property abbreviation is reserv.
|
|
rstchown
|
Boolean
|
on
|
Indicates whether the file system owner can grant file
ownership changes. The default is to restrict
chown operations. When
rstchown is set to off, the user has the
PRIV_FILE_CHOWN_SELF privilege for
chown operations. |
|
secondarycache
|
String
|
all
|
Controls what is cached in the secondary cache (L2ARC).
Possible values are all, none,
and metadata. If set to all,
both user data and metadata are cached. If set to
none, neither user data nor metadata is
cached. If set to metadata, only metadata is
cached. |
|
setuid
|
Boolean
|
on
|
Controls whether the setuid bit is
honored in a file system. |
|
shadow
|
String
|
None
|
Identifies a ZFS file system as a
shadow of the file system described by the
URI. Data is migrated to a shadow
file system with this property set from the file system identified
by the URI. The file system to be migrated must be read-only for a
complete migration. |
|
share.nfs
|
String
|
off
|
Controls whether an NFS share of a ZFS file system is
created and published and what options are used. You can also
publish and unpublish an NFS share by using the zfs
share and zfs unshare commands.
Using the zfs share command to publish an NFS
share requires that an NFS share property is also set. For
information about setting NFS share properties, see Sharing and Unsharing ZFS File Systems. |
|
share.smb
|
String
|
off
|
Controls whether a SMB share of a ZFS file system is
created and published and what options are used. You can also
publish and unpublish an SMB share by using the zfs
share and zfs unshare commands.
Using the zfs share command to publish an SMB
share require that an SMB share property is also set. For
information about setting SMB share properties, see Sharing and Unsharing ZFS File Systems. |
|
snapdir
|
String
|
hidden
|
Controls whether the .zfs directory
is hidden or visible in the root of the file system. For more
information about using snapshots, see Overview of ZFS Snapshots. |
|
sync
|
String
|
standard
|
Determines the synchronous behavior of a file system's
transactions. Possible values are:
-
standard, the default value, which
means synchronous file system transactions, such as
fsync, O_DSYNC,
O_SYNC, and so on, are written to the
intent log.
-
always, ensures that
every file system transaction is
written and flushed to stable storage by a returning system
call. This value has a significant performance
penalty.
-
disabled, means that synchronous
requests are disabled. File system transactions are only
committed to stable storage on the next transaction group
commit, which might be after many seconds. This value gives
the best performance, with no risk of corrupting the
pool.
Caution -
This disabled value is very
dangerous because ZFS is ignoring the synchronous
transaction demands of applications, such as databases
or NFS operations. Setting this value on the currently
active root or /var file system
might result in unexpected behavior, application data
loss, or increased vulnerability to replay attacks. You
should only use this value if you fully understand all
the associated risks.
|
|
|
type
|
String
|
N/A
|
Read-only property that identifies the dataset type as
filesystem (file system or clone),
volume, or
snapshot. |
|
used
|
Number
|
N/A
|
Read-only property that identifies the amount of disk
space consumed by a dataset and all its descendents. |
|
usedbychildren
|
Number
|
off
|
Read-only property that identifies the amount of disk
space that is used by children of this dataset, which would be freed
if all the dataset's children were destroyed. The property
abbreviation is usedchild. |
|
usedbydataset
|
Number
|
off
|
Read-only property that identifies the amount of disk
space that is used by a dataset itself, which would be freed if the
dataset was destroyed, after first destroying any snapshots and
removing any refreservation reservations. The
property abbreviation is usedds. |
|
usedbyrefreservation
|
Number
|
off
|
Read-only property that identifies the amount of disk
space that is used by a refreservation set on a
dataset, which would be freed if the
refreservation was removed. The property
abbreviation is usedrefreserv. |
|
usedbysnapshots
|
Number
|
off
|
Read-only property that identifies the amount of disk
space that is consumed by snapshots of a dataset. In particular, it
is the amount of disk space that would be freed if all of this
dataset's snapshots were destroyed. Note that this value is not
simply the sum of the snapshots' used properties,
because space can be shared by multiple snapshots. The property
abbreviation is usedsnap. |
|
utf8only
|
Boolean
|
Off
|
This property indicates whether a file system should
reject file names that include characters that are not present in
the UTF-8 character code set. If this property is explicitly set to
off, the normalization
property must either not be explicitly set or be set to
none. The default value for the
utf8only property is off.
This property cannot be changed after the file system is
created. |
|
version
|
Number
|
N/A
|
Identifies the on-disk version of a file system, which
is independent of the pool version. This property can only be set to
a later version that is available from the supported software
release. For more information, see the zfs
upgrade command. |
|
volblocksize
|
Number
|
8 KB
|
For volumes, specifies the block size of the volume. The
block size cannot be changed after the volume has been written, so
set the block size at volume creation time. The default block size
for volumes is 8 KB. Any power of 2 from 512 bytes to 128 KB is
valid. The property abbreviation is volblock.
|
|
volsize
|
Number
|
N/A
|
For volumes, specifies the logical size of the
volume. |
|
vscan
|
Boolean
|
Off
|
Controls whether regular files should be scanned for
viruses when a file is opened and closed. In addition to enabling
this property, a virus scanning service must also be enabled for
virus scanning to occur if you have third-party virus scanning
software. The default value is off. |
|
xattr
|
Boolean
|
on
|
Indicates whether extended attributes are enabled
( on) or disabled ( off) for
this file system. |
|
zoned
|
Boolean
|
N/A
|
Indicates whether a file system has been added to a
non-global zone. If this property is set, then the mount point is
not honored in the global zone, and ZFS cannot mount such a file
system when requested. When a zone is first installed, this property
is set for any added file systems. |
|
ZFS Read-Only Native Properties
Read-only native properties can be retrieved but not set. Read-only native properties are not inherited. Some native properties are specific to a particular type of dataset. In such cases, the dataset type is mentioned in the description in Figure 3, Table 3, ZFS Native Property Descriptions.
One example of this type of property is the used property.
The used property is a read-only property that identifies the amount of disk space consumed by this dataset and all its descendents. This value is checked against the dataset's quota and reservation. The disk space used does not include the dataset's reservation, but does consider the reservation of any descendent datasets. The amount of disk space that a dataset consumes from its parent, as well as the amount of disk space that is freed if the dataset is recursively destroyed, is the greater of its space used and its reservation.
When snapshots are created, their disk space is initially shared between the snapshot and the file system, and possibly with previous snapshots. As the file system changes, disk space that was previously shared becomes unique to the snapshot and is counted in the snapshot's space used. The disk space that is used by a snapshot accounts for its unique data. Additionally, deleting snapshots can increase the amount of disk space unique to (and used by) other snapshots.
The amount of disk space used, available, and referenced does not include pending changes. Pending changes are generally accounted for within a few seconds. Committing a change to a disk using the fsync(3c) or O_SYNC function does not necessarily guarantee that the disk space usage information will be updated immediately.
The usedbychildren, usedbydataset, usedbyrefreservation, and usedbysnapshots property information can be displayed with the zfs list
–o space command. These properties identify the used property into disk space that is consumed by descendents. For more information, see Figure 3, Table 3, ZFS Native Property Descriptions.
Settable ZFS Native Properties
Settable native properties are properties whose values can be both retrieved and
set. Settable native properties are set by using the zfs set
command, as described in Setting ZFS Properties or
by using the zfs create command as described in How to Create a ZFS File System. With the exceptions
of quotas and reservations, settable native properties are inherited. For more
information about quotas and reservations, see Setting ZFS Quotas and Reservations.
Some settable native properties are specific to a particular type of dataset. In
such cases, the dataset type is mentioned in the description in Figure 3, Table 3, ZFS Native Property Descriptions. If not specifically
mentioned, a property applies to all dataset types: file systems, volumes, clones,
and snapshots.
The canmount Property
If the canmount property is set to off,
the file system cannot be mounted by using the zfs mount or
zfs mount
–a commands. Setting this property to off is
similar to setting the mountpoint property to
none, except that the file system still has a normal
mountpoint property that can be inherited. For example,
you can set this property to off, establish inheritable
properties for descendent file systems, but the parent file system itself is
never mounted nor is it accessible to users. In this case, the parent file
system is serving as a container so that you can set
properties on the container, but the container itself is never
accessible.
In the following example, userpool is created, and its
canmount property is set to off.
Mount points for descendent user file systems are set to one common mount point,
/export/home. Properties that are set on the parent
file system are inherited by descendent file systems, but the parent file system
itself is never mounted.
# zpool create userpool mirror c0t5d0 c1t6d0
# zfs set canmount=off userpool
# zfs set mountpoint=/export/home userpool
# zfs set compression=on userpool
# zfs create userpool/user1
# zfs create userpool/user2
# zfs mount
userpool/user1 /export/home/user1
userpool/user2 /export/home/user2
Setting the canmount property to noauto
means that the file system can only be mounted explicitly, not
automatically.
The casesensitivity Property
This property indicates whether the file name matching algorithm used by the
file system should be casesensitive,
caseinsensitive, or allow a combination of both styles of
matching (mixed).
When a case-insensitive matching request is made of a
mixed sensitivity file system, the behavior is
generally the same as would be expected of a purely case-insensitive file
system. The difference is that a mixed sensitivity file system might contain
directories with multiple names that are unique from a case-sensitive
perspective, but not unique from the case-insensitive perspective.
For example, a directory might contain files foo,
Foo, and FOO. If a request is made
to case-insensitively match any of the possible forms of
foo, (for example foo,
FOO, FoO,
fOo, and so on) one of the three existing files is chosen
as the match by the matching algorithm. Exactly which file the algorithm chooses
as a match is not guaranteed, but what is guaranteed is that the same file is
chosen as a match for any of the forms of foo. The file
chosen as a case-insensitive match for foo,
FOO, foO,
Foo, and so on, is always the same, so long as the
directory remains unchanged.
The utf8only, normalization, and
casesensitivity properties also provide new permissions
that can be assigned to non-privileged users by using ZFS delegated
administration. For more information, see Delegating ZFS Permissions.
The copies Property
As a reliability feature, ZFS file system metadata is automatically stored
multiple times across different disks, if possible. This feature is known as
ditto blocks.
In this release, you can also store multiple copies of user data is also
stored per file system by using the zfs set copies command.
For example:
# zfs set copies=2 users/home
# zfs get copies users/home
NAME PROPERTY VALUE SOURCE
users/home copies 2 local
Available values are 1, 2, or 3. The default value is 1. These copies are in
addition to any pool-level redundancy, such as in a mirrored or RAID-Z
configuration.
The benefits of storing multiple copies of ZFS user data are as
follows:
-
Improves data retention by enabling recovery from unrecoverable block
read faults, such as media faults (commonly known as bit
rot) for all ZFS configurations.
-
Provides data protection, even when only a single disk is
available.
-
Enables you to select data protection policies on a per-file system
basis, beyond the capabilities of the storage pool.
Note -
Depending on the allocation of the ditto blocks in the storage pool,
multiple copies might be placed on a single disk. A subsequent full disk
failure might cause all ditto blocks to be unavailable.
You might consider using ditto blocks when you accidentally create a
non-redundant pool and when you need to set data retention policies.
The dedup Property
The dedup property controls whether duplicate data is
removed from a file system. If a file system has the dedup
property enabled, duplicate data blocks are removed synchronously. The result is
that only unique data is stored and common components are shared between
files.
Do not enable the dedup property on file systems that
reside on production systems until you review the following
considerations:
-
Determine if your data would benefit from deduplication space savings.
You can run the zdb
–S command to simulate the potential space savings of
enabling dedup on your pool. This command must be run on a quiet pool.
If your data is not dedup-able, then there's not point in enabling
dedup. For example:
# zdb -S tank
Simulated DDT histogram:
bucket allocated referenced
______ ______________________________ ______________________________
refcnt blocks LSIZE PSIZE DSIZE blocks LSIZE PSIZE DSIZE
------ ------ ----- ----- ----- ------ ----- ----- -----
1 2.27M 239G 188G 194G 2.27M 239G 188G 194G
2 327K 34.3G 27.8G 28.1G 698K 73.3G 59.2G 59.9G
4 30.1K 2.91G 2.10G 2.11G 152K 14.9G 10.6G 10.6G
8 7.73K 691M 529M 529M 74.5K 6.25G 4.79G 4.80G
16 673 43.7M 25.8M 25.9M 13.1K 822M 492M 494M
32 197 12.3M 7.02M 7.03M 7.66K 480M 269M 270M
64 47 1.27M 626K 626K 3.86K 103M 51.2M 51.2M
128 22 908K 250K 251K 3.71K 150M 40.3M 40.3M
256 7 302K 48K 53.7K 2.27K 88.6M 17.3M 19.5M
512 4 131K 7.50K 7.75K 2.74K 102M 5.62M 5.79M
2K 1 2K 2K 2K 3.23K 6.47M 6.47M 6.47M
8K 1 128K 5K 5K 13.9K 1.74G 69.5M 69.5M
Total 2.63M 277G 218G 225G 3.22M 337G 263G 270G
dedup = 1.20, compress = 1.28, copies = 1.03, dedup * compress / copies = 1.50
If the estimated dedup ratio is greater than 2, then you might see
dedup space savings.
In the above example, the dedup ratio is less than 2, so enabling
dedup is not recommended.
-
Make sure your system has enough memory to support dedup.
-
Each in-core dedup table entry is approximately 320
bytes
-
Multiply the number of allocated blocks times 320. For
example:
in-core DDT size = 2.63M x 320 = 841.60M
-
Dedup performance is best when the deduplication table fits into
memory. If the dedup table has to be written to disk, then performance
will decrease. For example, removing a large file system with dedup
enabled will severely decrease system performance if the system doesn't
meet the memory requirements described above.
When dedup is enabled, the dedup
checksum algorithm overrides the checksum property. Setting
the property value to verify is equivalent to specifying
sha256,verify. If the property is set to
verify and two blocks have the same signature, ZFS does a
byte-by-byte comparison with the existing block to ensure that the contents are
identical.
This property can be enabled per file system. For example:
# zfs set dedup=on tank/home
You can use the zfs get command to determine if the
dedup property is set.
Although deduplication is set as a file system property, the scope is
pool-wide. For example, you can identify the deduplication ratio. For
example:
# zpool list tank
NAME SIZE ALLOC FREE CAP DEDUP HEALTH ALTROOT
rpool 136G 55.2G 80.8G 40% 2.30x ONLINE -
The DEDUP column indicates how much deduplication has
occurred. If the dedup property is not enabled on any file
system or if the dedup property was just enabled on the file
system, the DEDUP ratio is 1.00x.
You can use the zpool get command to determine the value of
the dedupratio property. For example:
# zpool get dedupratio export
NAME PROPERTY VALUE SOURCE
rpool dedupratio 3.00x -
This pool property illustrates how much data deduplication this pool has
achieved.
The encryption Property
You can use the encryption property to encrypt ZFS file systems. For more
information, see Encrypting ZFS File Systems.
The recordsize Property
The recordsize property 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 adjust block sizes according to
internal algorithms optimized for typical access patterns. For databases that
create very large files but access the files in small random chunks, these
algorithms might be suboptimal. Specifying a recordsize
value 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 might adversely affect performance. The size
specified must be a power of 2 greater than or equal to 512 bytes and less than
or equal to 1 MB. Changing the file system's recordsize value
only affects files created afterward. Existing files are unaffected.
The property abbreviation is recsize.
The share.smb Property
This property enables sharing of ZFS file systems with the Oracle Solaris SMB service,
and identifies options to be used.
When the property is changed from off to on, any shares that inherit the
property are re-shared with their current options. When the property is set to
off, the shares that inherit the property are unshared.
For examples of using the share.smb property, see
Sharing and Unsharing ZFS File Systems.
The volsize Property
The volsize property specifies 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 users. A volume that 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 the volume is in use, particularly when you shrink the size. Use
extreme care when adjusting the volume size.
For more information about using volumes, see ZFS Volumes.
ZFS User Properties
In addition to the native properties, ZFS supports arbitrary user properties. User
properties have no effect on ZFS behavior, but you can use them to annotate datasets
with information that is meaningful in your environment.
User property names must conform to the following conventions:
-
They must contain a colon (':') character to distinguish them from native
properties.
-
They must contain lowercase letters, numbers, or the following punctuation
characters: ':', '+','.', '_'.
-
The maximum length of a user property name is 256 characters.
The expected convention is that the property name is divided into the following
two components but this namespace is not enforced by ZFS:
module:property
When making programmatic use of user properties, use a reversed DNS domain name
for the module component of property names to reduce the
chance that two independently developed packages will use the same property name for
different purposes. Property names that begin with com.oracle.
are reserved for use by Oracle Corporation.
The values of user properties must conform to the following conventions:
For example:
# zfs set dept:users=finance userpool/user1
# zfs set dept:users=general userpool/user2
# zfs set dept:users=itops userpool/user3
All of the commands that operate on properties, such as zfs
list, zfs get, zfs set, and so
on, can be used to manipulate both native properties and user properties.
For example:
zfs get -r dept:users userpool
NAME PROPERTY VALUE SOURCE
userpool dept:users all local
userpool/user1 dept:users finance local
userpool/user2 dept:users general local
userpool/user3 dept:users itops local
To clear a user property, use the zfs inherit command. For
example:
# zfs inherit -r dept:users userpool
If the property is not defined in any parent dataset, it is removed
entirely.