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7276 zfs(1m) manpage could better describe space properties

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illumos/illumos-gate@5749c35234
5749c35234

https://www.illumos.org/issues/7276
  The "used" and "written" properties could be described better by the zfs.1m
  manpage.
  "written" could be better described as "The amount of space referenced by this
  dataset, that was written since the previous snapshot (i.e. that is not
  referenced by the previous snapshot)."
  The "used" section needs more work, but at a minimum it could say that the
  "used" space of a snapshot is the space unique to the snapshot (i.e. the space
  referenced only by this snapshot). The "used" space of a snapshot is a subset
  of the "written" space of the snapshot.

Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Robert Mustacchi <rm@joyent.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Author: Pavel Zakharov <pavel.zakharov@delphix.com>
This commit is contained in:
Andriy Gapon 2017-04-14 17:59:10 +00:00
parent b689d45202
commit cce6c1c241
1 changed files with 18 additions and 11 deletions
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29
man/man1m/zfs.1m
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@ -21,7 +21,7 @@
.\"
.\" Copyright (c) 2009 Sun Microsystems, Inc. All Rights Reserved.
.\" Copyright 2011 Joshua M. Clulow <josh@sysmgr.org>
.\" Copyright (c) 2011, 2015 by Delphix. All rights reserved.
.\" Copyright (c) 2011, 2016 by Delphix. All rights reserved.
.\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
.\" Copyright (c) 2014, Joyent, Inc. All rights reserved.
.\" Copyright (c) 2014 by Adam Stevko. All rights reserved.
@ -615,22 +615,27 @@ The amount of space consumed by this dataset and all its descendents. 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 descendent datasets. The amount of space that a
dataset consumes from its parent, as well as the amount of space that are freed
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.
.Pp
When snapshots
The used space of a snapshot
.Po see the
.Sx Snapshots
section
.Pc
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
.Pq and used by
other snapshots.
is space that is referenced exclusively by this snapshot. If this snapshot is
destroyed, the amount of
.Sy used
space will be freed. Space that is shared by multiple snapshots isn't accounted
for in this metric. When a snapshot is destroyed, space that was previously
shared with this snapshot can become unique to snapshots adjacent to it, thus
changing the used space of those snapshots. The used space of the latest
snapshot can also be affected by changes in the file system. Note that the
.Sy used
space of a snapshot is a subset of the
.Sy written
space of the snapshot.
.Pp
The amount of space used, available, or referenced does not take into account
pending changes. Pending changes are generally accounted for within a few
@ -754,8 +759,10 @@ 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,
.Sy volblock .
.It Sy written
The amount of
The amount of space
.Sy referenced
by this dataset, that was written since the previous snapshot
.Pq i.e. that is not referenced by the previous snapshot .
space written to this dataset since the previous snapshot.
.It Sy written Ns @ Ns Em snapshot
The amount of