Use macros for quotes and such
Use Dq,Pq/Po/Pc macros. illumos dumpadm is now in section 8. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Toomas Soome <tsoome@me.com> Closes #13586
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@ -18,7 +18,7 @@
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.\" Copyright (c) 2019, Allan Jude
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.\" Copyright (c) 2021, Colm Buckley <colm@tuatha.org>
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.\"
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.Dd May 31, 2021
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.Dd June 23, 2022
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.Dt ZPOOL-FEATURES 7
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.Os
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.
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@ -27,8 +27,10 @@
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.Nd description of ZFS pool features
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.
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.Sh DESCRIPTION
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ZFS pool on-disk format versions are specified via "features" which replace
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the old on-disk format numbers (the last supported on-disk format number is 28).
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ZFS pool on-disk format versions are specified via
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.Dq features
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which replace the old on-disk format numbers
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.Pq the last supported on-disk format number is 28 .
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To enable a feature on a pool use the
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.Nm zpool Cm upgrade ,
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or set the
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@ -62,10 +64,12 @@ implementation that created the pool for information about those features.
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Each supported feature also has a short name.
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By convention a feature's short name is the portion of its GUID which follows the
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.Sq \&:
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(i.e.
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.Po
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i.e.
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.Ar com.example : Ns Ar feature-name
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would have the short name
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.Ar feature-name ) ,
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.Ar feature-name
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.Pc ,
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however a feature's short name may differ across ZFS implementations if
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following the convention would result in name conflicts.
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.
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@ -110,9 +114,11 @@ These features are referred to as
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If all unsupported features on a pool are read-only compatible,
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the pool can be imported in read-only mode by setting the
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.Sy readonly
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property during import (see
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property during import
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.Po see
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.Xr zpool-import 8
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for details on importing pools).
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for details on importing pools
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.Pc .
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.
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.Ss Unsupported features
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For each unsupported feature enabled on an imported pool, a pool property
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@ -143,15 +149,19 @@ The
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feature facilitates this by allowing feature sets to be read from text files.
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When set to
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.Sy off
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(the default), compatibility feature sets are disabled
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(i.e. all features are enabled); when set to
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.Pq the default ,
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compatibility feature sets are disabled
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.Pq i.e. all features are enabled ;
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when set to
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.Sy legacy ,
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no features are enabled.
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When set to a comma-separated list of filenames
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(each filename may either be an absolute path, or relative to
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.Po
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each filename may either be an absolute path, or relative to
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.Pa /etc/zfs/compatibility.d
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or
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.Pa /usr/share/zfs/compatibility.d ) ,
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.Pa /usr/share/zfs/compatibility.d
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.Pc ,
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the lists of requested features are read from those files,
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separated by whitespace and/or commas.
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Only features present in all files are enabled.
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@ -291,7 +301,9 @@ This feature enables support for separate allocation classes.
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.Pp
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This feature becomes
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.Sy active
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when a dedicated allocation class vdev (dedup or special) is created with the
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when a dedicated allocation class vdev
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.Pq dedup or special
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is created with the
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.Nm zpool Cm create No or Nm zpool Cm add No commands .
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With device removal, it can be returned to the
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.Sy enabled
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@ -356,8 +368,9 @@ state when all v2 bookmarks are destroyed.
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.feature com.delphix bookmark_written no bookmark extensible_dataset bookmark_v2
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This feature enables additional bookmark accounting fields, enabling the
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.Sy written Ns # Ns Ar bookmark
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property (space written since a bookmark) and estimates of
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send stream sizes for incrementals from bookmarks.
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property
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.Pq space written since a bookmark
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and estimates of send stream sizes for incrementals from bookmarks.
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.Pp
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This feature becomes
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.Sy active
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@ -372,7 +385,8 @@ This feature enables the ability for the
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and
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.Nm zpool Cm replace
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commands to perform sequential reconstruction
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(instead of healing reconstruction) when resilvering.
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.Pq instead of healing reconstruction
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when resilvering.
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.Pp
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Sequential reconstruction resilvers a device in LBA order without immediately
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verifying the checksums.
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@ -424,8 +438,10 @@ vdev to an existing pool.
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.
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.feature org.illumos edonr no extensible_dataset
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This feature enables the use of the Edon-R hash algorithm for checksum,
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including for nopwrite (if compression is also enabled, an overwrite of
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a block whose checksum matches the data being written will be ignored).
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including for nopwrite
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.Po if compression is also enabled, an overwrite of
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a block whose checksum matches the data being written will be ignored
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.Pc .
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In an abundance of caution, Edon-R requires verification when used with
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dedup:
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.Nm zfs Cm set Sy dedup Ns = Ns Sy edonr , Ns Sy verify
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@ -433,13 +449,15 @@ dedup:
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.Pp
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Edon-R is a very high-performance hash algorithm that was part
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of the NIST SHA-3 competition.
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It provides extremely high hash performance (over 350% faster than SHA-256),
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It provides extremely high hash performance
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.Pq over 350% faster than SHA-256 ,
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but was not selected because of its unsuitability
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as a general purpose secure hash algorithm.
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This implementation utilizes the new salted checksumming functionality
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in ZFS, which means that the checksum is pre-seeded with a secret
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256-bit random key (stored on the pool) before being fed the data block
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to be checksummed.
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256-bit random key
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.Pq stored on the pool
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before being fed the data block to be checksummed.
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Thus the produced checksums are unique to a given pool,
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preventing hash collision attacks on systems with dedup.
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.Pp
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@ -452,10 +470,15 @@ Blocks whose contents can compress to 112 bytes
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or smaller can take advantage of this feature.
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.Pp
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When this feature is enabled, the contents of highly-compressible blocks are
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stored in the block "pointer" itself (a misnomer in this case, as it contains
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the compressed data, rather than a pointer to its location on disk).
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Thus the space of the block (one sector, typically 512 B or 4 KiB) is saved,
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and no additional I/O is needed to read and write the data block.
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stored in the block
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.Dq pointer
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itself
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.Po a misnomer in this case, as it contains
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the compressed data, rather than a pointer to its location on disk
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.Pc .
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Thus the space of the block
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.Pq one sector, typically 512 B or 4 KiB
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is saved, and no additional I/O is needed to read and write the data block.
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.
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\*[instant-never]
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.
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@ -465,7 +488,9 @@ number of snapshots of a single filesystem or volume, and also reduces
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the disk space required.
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.Pp
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When there are many snapshots, each snapshot uses many Block Pointer
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Objects (bpobjs) to track blocks associated with that snapshot.
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Objects
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.Pq bpobjs
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to track blocks associated with that snapshot.
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However, in common use cases, most of these bpobjs are empty.
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This feature allows us to create each bpobj on-demand,
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thus eliminating the empty bpobjs.
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@ -536,7 +561,12 @@ will not match the source.
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Its use by
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.Nm zfs Cm send Fl i
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has been disabled by default
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.Pq see Sy send_holes_without_birth_time No in Xr zfs 4 .
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.Po
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see
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.Sy send_holes_without_birth_time
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in
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.Xr zfs 4
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.Pc .
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.Pp
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This feature improves performance of incremental sends
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.Pq Nm zfs Cm send Fl i
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@ -549,8 +579,10 @@ contains information about every block that changed between
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.Sy A No and Sy B .
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Blocks which did not change between those snapshots can be
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identified and omitted from the stream using a piece of metadata called
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the "block birth time", but birth times are not recorded for holes
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(blocks filled only with zeroes).
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the
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.Dq block birth time ,
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but birth times are not recorded for holes
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.Pq blocks filled only with zeroes .
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Since holes created after
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.Sy A No cannot be distinguished from holes created before Sy A ,
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information about every hole in the entire filesystem or zvol
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@ -558,9 +590,9 @@ is included in the send stream.
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.Pp
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For workloads where holes are rare this is not a problem.
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However, when incrementally replicating filesystems or zvols with many holes
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(for example a zvol formatted with another filesystem) a lot of time will
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be spent sending and receiving unnecessary information about holes that
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already exist on the receiving side.
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.Pq for example a zvol formatted with another filesystem
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a lot of time will be spent sending and receiving unnecessary information
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about holes that already exist on the receiving side.
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.Pp
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Once the
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.Sy hole_birth
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@ -657,7 +689,7 @@ When the
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feature is set to
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.Sy enabled ,
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the administrator can use
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.Xr dumpadm 1M
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.Xr dumpadm 8
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to configure a dump device on a pool comprised of multiple vdevs.
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.Pp
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Under
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@ -677,7 +709,9 @@ This feature is an enhancement of
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.Sy device_removal ,
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which will over time reduce the memory used to track removed devices.
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When indirect blocks are freed or remapped,
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we note that their part of the indirect mapping is "obsolete" – no longer needed.
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we note that their part of the indirect mapping is
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.Dq obsolete
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– no longer needed.
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.Pp
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This feature becomes
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.Sy active
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@ -688,7 +722,8 @@ command is used on a top-level vdev, and will never return to being
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.
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.feature org.zfsonlinux project_quota yes extensible_dataset
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This feature allows administrators to account the spaces and objects usage
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information against the project identifier (ID).
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information against the project identifier
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.Pq ID .
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.Pp
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The project ID is an object-based attribute.
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When upgrading an existing filesystem,
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@ -698,7 +733,8 @@ their parent directories' project ID if the parent's inherit flag is set
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.Pq via Nm chattr Sy [+-]P No or Nm zfs Cm project Fl s Ns | Ns Fl C .
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Otherwise, the new object's project ID will be zero.
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An object's project ID can be changed at any time by the owner
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(or privileged user) via
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.Pq or privileged user
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via
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.Nm chattr Fl p Ar prjid
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or
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.Nm zfs Cm project Fl p Ar prjid .
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@ -740,7 +776,8 @@ when the deferred resilver begins.
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.
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.feature org.illumos sha512 no extensible_dataset
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This feature enables the use of the SHA-512/256 truncated hash algorithm
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(FIPS 180-4) for checksum and dedup.
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.Pq FIPS 180-4
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for checksum and dedup.
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The native 64-bit arithmetic of SHA-512 provides an approximate 50%
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performance boost over SHA-256 on 64-bit hardware
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and is thus a good minimum-change replacement candidate
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@ -756,11 +793,12 @@ This feature enables the use of the Skein hash algorithm for checksum and dedup.
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Skein is a high-performance secure hash algorithm that was a
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finalist in the NIST SHA-3 competition.
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It provides a very high security margin and high performance on 64-bit hardware
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(80% faster than SHA-256).
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.Pq 80% faster than SHA-256 .
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This implementation also utilizes the new salted checksumming
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functionality in ZFS, which means that the checksum is pre-seeded with a
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secret 256-bit random key (stored on the pool) before being fed the data
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block to be checksummed.
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secret 256-bit random key
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.Pq stored on the pool
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before being fed the data block to be checksummed.
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Thus the produced checksums are unique to a given pool,
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preventing hash collision attacks on systems with dedup.
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.Pp
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@ -778,7 +816,9 @@ and never returns back to being
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.
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.feature com.delphix spacemap_v2 yes
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This feature enables the use of the new space map encoding which
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consists of two words (instead of one) whenever it is advantageous.
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consists of two words
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.Pq instead of one
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whenever it is advantageous.
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The new encoding allows space maps to represent large regions of
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space more efficiently on-disk while also increasing their maximum
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addressable offset.
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@ -872,4 +912,5 @@ are destroyed.
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.El
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.
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.Sh SEE ALSO
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.Xr zfs 8 ,
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.Xr zpool 8
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