Index: head/cddl/contrib/opensolaris/cmd/zpool/zpool-features.7
===================================================================
--- head/cddl/contrib/opensolaris/cmd/zpool/zpool-features.7	(revision 363223)
+++ head/cddl/contrib/opensolaris/cmd/zpool/zpool-features.7	(revision 363224)
@@ -1,675 +1,674 @@
 '\" te
 .\" Copyright (c) 2012, Martin Matuska <mm@FreeBSD.org>.
 .\" All Rights Reserved.
 .\"
 .\" The contents of this file are subject to the terms of the
 .\" Common Development and Distribution License (the "License").
 .\" You may not use this file except in compliance with the License.
 .\"
 .\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 .\" or http://www.opensolaris.org/os/licensing.
 .\" See the License for the specific language governing permissions
 .\" and limitations under the License.
 .\"
 .\" When distributing Covered Code, include this CDDL HEADER in each
 .\" file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 .\" If applicable, add the following below this CDDL HEADER, with the
 .\" fields enclosed by brackets "[]" replaced with your own identifying
 .\" information: Portions Copyright [yyyy] [name of copyright owner]
 .\"
 .\" Copyright (c) 2012, 2017 by Delphix. All rights reserved.
 .\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
 .\" Copyright (c) 2013, Joyent, Inc. All rights reserved.
 .\"
 .\" $FreeBSD$
 .\"
 .Dd August 16, 2019
 .Dt ZPOOL-FEATURES 7
 .Os
 .Sh NAME
 .Nm zpool-features
 .Nd ZFS pool feature descriptions
 .Sh DESCRIPTION
 ZFS pool on\-disk format versions are specified via "features" which replace
 the old on\-disk format numbers (the last supported on\-disk format number is
 28).
 To enable a feature on a pool use the
 .Cm upgrade
 subcommand of the
 .Xr zpool 8
 command, or set the
 .Sy feature@feature_name
 property to
 .Ar enabled .
 .Pp
 The pool format does not affect file system version compatibility or the ability
 to send file systems between pools.
 .Pp
 Since most features can be enabled independently of each other the on\-disk
 format of the pool is specified by the set of all features marked as
 .Sy active
 on the pool.
 If the pool was created by another software version this set may
 include unsupported features.
 .Ss Identifying features
 Every feature has a guid of the form
 .Sy com.example:feature_name .
 The reverse DNS name ensures that the feature's guid is unique across all ZFS
 implementations.
 When unsupported features are encountered on a pool they will
 be identified by their guids.
 Refer to the documentation for the ZFS implementation that created the pool
 for information about those features.
 .Pp
 Each supported feature also has a short name.
 By convention a feature's short name is the portion of its guid which follows
 the ':' (e.g.
 .Sy com.example:feature_name
 would have the short name
 .Sy feature_name ),
 however a feature's short name may differ across ZFS implementations if
 following the convention would result in name conflicts.
 .Ss Feature states
 Features can be in one of three states:
 .Bl -tag -width "XXXXXXXX"
 .It Sy active
 This feature's on\-disk format changes are in effect on the pool.
 Support for this feature is required to import the pool in read\-write mode.
 If this feature is not read-only compatible, support is also required to
 import the pool in read\-only mode (see "Read\-only compatibility").
 .It Sy enabled
 An administrator has marked this feature as enabled on the pool, but the
 feature's on\-disk format changes have not been made yet.
 The pool can still be imported by software that does not support this feature,
 but changes may be made to the on\-disk format at any time which will move
 the feature to the
 .Sy active
 state.
 Some features may support returning to the
 .Sy enabled
 state after becoming
 .Sy active .
 See feature\-specific documentation for details.
 .It Sy disabled
 This feature's on\-disk format changes have not been made and will not be made
 unless an administrator moves the feature to the
 .Sy enabled
 state.
 Features cannot be disabled once they have been enabled.
 .El
 .Pp
 The state of supported features is exposed through pool properties of the form
 .Sy feature@short_name .
 .Ss Read\-only compatibility
 Some features may make on\-disk format changes that do not interfere with other
 software's ability to read from the pool.
 These features are referred to as "read\-only compatible".
 If all unsupported features on a pool are read\-only compatible, the pool can
 be imported in read\-only mode by setting the
 .Sy readonly
 property during import (see
 .Xr zpool 8
 for details on importing pools).
 .Ss Unsupported features
 For each unsupported feature enabled on an imported pool a pool property
 named
 .Sy unsupported@feature_guid
 will indicate why the import was allowed despite the unsupported feature.
 Possible values for this property are:
 .Bl -tag -width "XXXXXXXX"
 .It Sy inactive
 The feature is in the
 .Sy enabled
 state and therefore the pool's on\-disk format is still compatible with
 software that does not support this feature.
 .It Sy readonly
 The feature is read\-only compatible and the pool has been imported in
 read\-only mode.
 .El
 .Ss Feature dependencies
 Some features depend on other features being enabled in order to function
 properly.
 Enabling a feature will automatically enable any features it depends on.
 .Sh FEATURES
 The following features are supported on this system:
 .Bl -tag -width "XXXXXXXX"
 .It Sy async_destroy
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:async_destroy"
 .It GUID Ta com.delphix:async_destroy
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta none
 .El
 .Pp
 Destroying a file system requires traversing all of its data in order to
 return its used space to the pool.
 Without
 .Sy async_destroy
 the file system is not fully removed until all space has been reclaimed.
 If the destroy operation is interrupted by a reboot or power outage the next
 attempt to open the pool will need to complete the destroy operation
 synchronously.
 .Pp
 When
 .Sy async_destroy
 is enabled the file system's data will be reclaimed by a background process,
 allowing the destroy operation to complete without traversing the entire file
 system.
 The background process is able to resume interrupted destroys after the pool
 has been opened, eliminating the need to finish interrupted destroys as part
 of the open operation.
 The amount of space remaining to be reclaimed by the background process is
 available through the
 .Sy freeing
 property.
 .Pp
 This feature is only
 .Sy active
 while
 .Sy freeing
 is non\-zero.
 .It Sy empty_bpobj
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:empty_bpobj"
 .It GUID Ta com.delphix:empty_bpobj
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature increases the performance of creating and using a large number
 of snapshots of a single filesystem or volume, and also reduces the disk
 space required.
 .Pp
 When there are many snapshots, each snapshot uses many Block Pointer Objects
 .Pq bpobj's
 to track blocks associated with that snapshot.
 However, in common use cases, most of these bpobj's are empty.
 This feature allows us to create each bpobj on-demand, thus eliminating the
 empty bpobjs.
 .Pp
 This feature is
 .Sy active
 while there are any filesystems, volumes, or snapshots which were created
 after enabling this feature.
 .It Sy filesystem_limits
 .Bl -column "READ\-ONLY COMPATIBLE" "com.joyent:filesystem_limits"
 .It GUID Ta com.joyent:filesystem_limits
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta extensible_dataset
 .El
 .Pp
 This feature enables filesystem and snapshot limits.
 These limits can be used
 to control how many filesystems and/or snapshots can be created at the point in
 the tree on which the limits are set.
 .Pp
 This feature is
 .Sy active
 once either of the limit properties has been
 set on a dataset.
 Once activated the feature is never deactivated.
 .It Sy lz4_compress
 .Bl -column "READ\-ONLY COMPATIBLE" "org.illumos:lz4_compress"
 .It GUID Ta org.illumos:lz4_compress
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta none
 .El
 .Pp
 .Sy lz4
 is a high-performance real-time compression algorithm that
 features significantly faster compression and decompression as well as a
 higher compression ratio than the older
 .Sy lzjb
 compression.
 Typically,
 .Sy lz4
 compression is approximately 50% faster on
 compressible data and 200% faster on incompressible data than
 .Sy lzjb .
 It is also approximately 80% faster on decompression, while
 giving approximately 10% better compression ratio.
 .Pp
 When the
 .Sy lz4_compress
 feature is set to
 .Sy enabled ,
 the
 administrator can turn on
 .Sy lz4
 compression on any dataset on the
 pool using the
 .Xr zfs 8
 command.
 Also, all newly written metadata
 will be compressed with
 .Sy lz4
 algorithm.
 Since this feature is not read-only compatible, this
 operation will render the pool unimportable on systems without support
 for the
 .Sy lz4_compress
 feature.
 Booting off of
 .Sy lz4
 -compressed root pools is supported.
 .Pp
 This feature becomes
 .Sy active
 as soon as it is enabled and will
 never return to being
 .Sy enabled .
 .It Sy multi_vdev_crash_dump
 .Bl -column "READ\-ONLY COMPATIBLE" "com.joyent:multi_vdev_crash_dump"
 .It GUID Ta com.joyent:multi_vdev_crash_dump
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature allows a dump device to be configured with a pool comprised
 of multiple vdevs.
 Those vdevs may be arranged in any mirrored or raidz
 configuration.
 .\" TODO: this is not yet supported on FreeBSD.
 .\" .Pp
 .\" When the
 .\" .Sy multi_vdev_crash_dump
 .\" feature is set to
 .\" .Sy enabled ,
 .\" the administrator can use the
 .\" .Xr dumpon 8
 .\" command to configure a
 .\" dump device on a pool comprised of multiple vdevs.
 .It Sy spacemap_histogram
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:spacemap_histogram"
 .It GUID Ta com.delphix:spacemap_histogram
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature allows ZFS to maintain more information about how free space
 is organized within the pool.
 If this feature is
 .Sy enabled ,
 ZFS will
 set this feature to
 .Sy active
 when a new space map object is created or
 an existing space map is upgraded to the new format.
 Once the feature is
 .Sy active ,
 it will remain in that state until the pool is destroyed.
 .It Sy extensible_dataset
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:extensible_dataset"
 .It GUID Ta com.delphix:extensible_dataset
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature allows more flexible use of internal ZFS data structures,
 and exists for other features to depend on.
 .Pp
 This feature will be
 .Sy active
 when the first dependent feature uses it,
 and will be returned to the
 .Sy enabled
 state when all datasets that use
 this feature are destroyed.
 .It Sy bookmarks
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:bookmarks"
 .It GUID Ta com.delphix:bookmarks
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta extensible_dataset
 .El
 .Pp
 This feature enables use of the
 .Nm zfs
 .Cm bookmark
 subcommand.
 .Pp
 This feature is
 .Sy active
 while any bookmarks exist in the pool.
 All bookmarks in the pool can be listed by running
 .Nm zfs
 .Cm list
 .Fl t No bookmark Fl r Ar poolname .
 .It Sy enabled_txg
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:enabled_txg"
 .It GUID Ta com.delphix:enabled_txg
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta none
 .El
 .Pp
 Once this feature is enabled ZFS records the transaction group number
 in which new features are enabled.
 This has no user-visible impact,
 but other features may depend on this feature.
 .Pp
 This feature becomes
 .Sy active
 as soon as it is enabled and will
 never return to being
 .Sy enabled .
 .It Sy hole_birth
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:hole_birth"
 .It GUID Ta com.delphix:hole_birth
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta enabled_txg
 .El
 .Pp
 This feature improves performance of incremental sends
 .Pq Dq zfs send -i
 and receives for objects with many holes.
 The most common case of
 hole-filled objects is zvols.
 .Pp
 An incremental send stream from snapshot
 .Sy A
 to snapshot
 .Sy B
 contains information about every block that changed between
 .Sy A
 and
 .Sy B .
 Blocks which did not change between those snapshots can be
 identified and omitted from the stream using a piece of metadata called
 the 'block birth time', but birth times are not recorded for holes
 .Pq blocks filled only with zeroes .
 Since holes created after
 .Sy A
 cannot be
 distinguished from holes created before
 .Sy A ,
 information about every
 hole in the entire filesystem or zvol is included in the send stream.
 .Pp
 For workloads where holes are rare this is not a problem.
 However, when
 incrementally replicating filesystems or zvols with many holes
 .Pq for example a zvol formatted with another filesystem
 a lot of time will
 be spent sending and receiving unnecessary information about holes that
 already exist on the receiving side.
 .Pp
 Once the
 .Sy hole_birth
 feature has been enabled the block birth times
 of all new holes will be recorded.
 Incremental sends between snapshots
 created after this feature is enabled will use this new metadata to avoid
 sending information about holes that already exist on the receiving side.
 .Pp
 This feature becomes
 .Sy active
 as soon as it is enabled and will
 never return to being
 .Sy enabled .
 .It Sy embedded_data
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:embedded_data"
 .It GUID Ta com.delphix:embedded_data
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature improves the performance and compression ratio of
 highly-compressible blocks.
 Blocks whose contents can compress to 112 bytes
 or smaller can take advantage of this feature.
 .Pp
 When this feature is enabled, the contents of highly-compressible blocks are
 stored in the block "pointer" itself
 .Po a misnomer in this case, as it contains
 the compressed data, rather than a pointer to its location on disk
 .Pc .
 Thus
 the space of the block
 .Pq one sector, typically 512 bytes or 4KB
 is saved,
 and no additional i/o is needed to read and write the data block.
 .Pp
 This feature becomes
 .Sy active
 as soon as it is enabled and will
 never return to being
 .Sy enabled .
 .It Sy zpool_checkpoint
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:zpool_checkpoint"
 .It GUID Ta com.delphix:zpool_checkpoint
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature enables the "zpool checkpoint" subcommand that can
 checkpoint the state of the pool at the time it was issued and later
 rewind back to it or discard it.
 .Pp
 This feature becomes
 .Sy active
 when the "zpool checkpoint" command is used to checkpoint the pool.
 The feature will only return back to being
 .Sy enabled
 when the pool is rewound or the checkpoint has been discarded.
 .It Sy device_removal
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:device_removal"
 .It GUID Ta com.delphix:device_removal
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature enables the "zpool remove" subcommand to remove top-level
 vdevs, evacuating them to reduce the total size of the pool.
 .Pp
 This feature becomes
 .Sy active
 when the "zpool remove" command is used
 on a top-level vdev, and will never return to being 
 .Sy enabled .
 .It Sy obsolete_counts
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:obsolete_counts"
 .It GUID Ta com.delphix:obsolete_counts
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta device_removal
 .El
 .Pp
 This feature is an enhancement of device_removal, which will over time
 reduce the memory used to track removed devices.  When indirect blocks
 are freed or remapped, we note that their part of the indirect mapping
 is "obsolete", i.e. no longer needed.  See also the "zfs remap"
 subcommand in
 .Xr zfs 8 .
 
 This feature becomes
 .Sy active
 when the "zpool remove" command is
 used on a top-level vdev, and will never return to being
 .Sy enabled .
 .It Sy spacemap_v2
 .Bl -column "READ\-ONLY COMPATIBLE" "com.delphix:spacemap_v2"
 .It GUID Ta com.delphix:spacemap_v2
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature enables the use of the new space map encoding which
 consists of two words (instead of one) whenever it is advantageous.
 The new encoding allows space maps to represent large regions of
 space more efficiently on-disk while also increasing their maximum
 addressable offset.
 .Pp
 This feature becomes
 .Sy active
 as soon as it is enabled and will
 never return to being
 .Sy enabled .
 .It Sy large_blocks
 .Bl -column "READ\-ONLY COMPATIBLE" "org.open-zfs:large_block"
 .It GUID Ta org.open-zfs:large_block
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta extensible_dataset
 .El
 .Pp
 The
 .Sy large_block
 feature allows the record size on a dataset to be
 set larger than 128KB.
 .Pp
 This feature becomes
 .Sy active
 once a
 .Sy recordsize
 property has been set larger than 128KB, and will return to being
 .Sy enabled
 once all filesystems that have ever had their recordsize larger than 128KB
 are destroyed.
 .Pp
-Please note that booting from datasets that have recordsize greater than
-128KB is
-.Em NOT
-supported by the
+Booting from datasets that use the
+.Sy large_block
+feature is supported by the
 .Fx
 boot loader.
 .It Sy large_dnode
 .Bl -column "READ\-ONLY COMPATIBLE" "org.zfsonlinux:large_dnode"
 .It GUID Ta org.zfsonlinux:large_dnode
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta extensible_dataset
 .El
 .Pp
 The
 .Sy large_dnode
 feature allows the size of dnodes in a dataset to be set larger than 512B.
 .Pp
 This feature becomes
 .Sy active
 once a dataset contains an object with a dnode larger than 512B,
 which occurs as a result of setting the
 .Sy dnodesize
 dataset property to a value other than
 .Sy legacy .
 The feature will return to being
 .Sy enabled
 once all filesystems that have ever contained a dnode larger than 512B are
 destroyed.
 Large dnodes allow more data to be stored in the bonus buffer, thus potentially
 improving performance by avoiding the use of spill blocks.
 .It Sy sha512
 .Bl -column "READ\-ONLY COMPATIBLE" "org.illumos:sha512"
 .It GUID Ta org.illumos:sha512
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta extensible_dataset
 .El
 .Pp
 The
 .Sy sha512
 feature enables the use of the SHA-512/256 truncated hash algorithm
 .Pq FIPS 180-4
 for checksum and dedup.
 The native 64-bit arithmetic of SHA-512 provides an approximate 50%
 performance boost over SHA-256 on 64-bit hardware and is thus a good
 minimum-change replacement candidate for systems where hash performance is
 important, but these systems cannot for whatever reason utilize the faster
 .Sy skein
 algorithms.
 .Pp
 When the
 .Sy sha512
 feature is set to
 .Sy enabled ,
 the administrator can turn on the
 .Sy sha512
 checksum on any dataset using the
 .Dl # zfs set checksum=sha512 Ar dataset
 command.
 This feature becomes
 .Sy active
 once a
 .Sy checksum
 property has been set to
 .Sy sha512 ,
 and will return to being
 .Sy enabled
 once all filesystems that have ever had their checksum set to
 .Sy sha512
 are destroyed.
 .It Sy skein
 .Bl -column "READ\-ONLY COMPATIBLE" "org.illumos:skein"
 .It GUID Ta org.illumos:skein
 .It READ\-ONLY COMPATIBLE Ta no
 .It DEPENDENCIES Ta extensible_dataset
 .El
 .Pp
 The
 .Sy skein
 feature enables the use of the Skein hash algorithm for checksum and dedup.
 Skein is a high-performance secure hash algorithm that was a finalist in the
 NIST SHA-3 competition.
 It provides a very high security margin and high performance on 64-bit hardware
 .Pq 80% faster than SHA-256 .
 This implementation also utilizes the new salted checksumming functionality in
 ZFS, which means that the checksum is pre-seeded with a secret 256-bit random
 key
 .Pq stored on the pool
 before being fed the data block to be checksummed.
 Thus the produced checksums are unique to a given pool, preventing hash
 collision attacks on systems with dedup.
 .Pp
 When the
 .Sy skein
 feature is set to
 .Sy enabled ,
 the administrator can turn on the
 .Sy skein
 checksum on any dataset using the
 .Dl # zfs set checksum=skein Ar dataset
 command.
 This feature becomes
 .Sy active
 once a
 .Sy checksum
 property has been set to
 .Sy skein ,
 and will return to being
 .Sy enabled
 once all filesystems that have ever had their checksum set to
 .Sy skein
 are destroyed.
 Booting off of pools using
 .Sy skein
 is supported.
 .It Sy allocation_classes
 .Bl -column "READ\-ONLY COMPATIBLE" "com.intel:allocation_classes"
 .It GUID Ta com.intel:allocation_classes
 .It READ\-ONLY COMPATIBLE Ta yes
 .It DEPENDENCIES Ta none
 .El
 .Pp
 This feature enables support for separate allocation classes.
 .Pp
 This feature becomes
 .Sy active
 when a dedicated allocation class vdev
 (dedup or special) is created with
 .Dq zpool create
 or
 .Dq zpool add .
 With device removal, it can be returned to the
 .Sy enabled
 state if all the top-level vdevs from an allocation class are removed.
 .El
 .Sh SEE ALSO
 .Xr zpool 8
 .Sh AUTHORS
 This manual page is a
 .Xr mdoc 7
 reimplementation of the
 .Tn illumos
 manual page
 .Em zpool-features(5) ,
 modified and customized for
 .Fx
 and licensed under the Common Development and Distribution License
 .Pq Tn CDDL .
 .Pp
 The
 .Xr mdoc 7
 implementation of this manual page was initially written by
 .An Martin Matuska Aq mm@FreeBSD.org .