9286 want refreservation=auto

When a ZFS volume is created with zfs create -V (but without -s), the
refreservation property is set to a value that is volsize plus the maximum
size of metadata. If refreservation is ever set to another value, it is
impossible to set it back to the automatically determined value. There are
other cases where refreservation may be wrong. These include receiving a
volume that was sent without properties and zfs clone.

We need:

zfs set refreservation=auto <volume>
zfs clone -o refreservation=auto <volume>

Each one would use the same function used by zfs create -V to determine the
proper value for refreservation.

illumos/illumos-gate@1c10ae76c0cb31326c320e7cef1d3f24a1f47125

Reviewed by: Allan Jude <allanjude@freebsd.org>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed by: Andy Stormont <astormont@racktopsystems.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Author: Mike Gerdts <mike.gerdts@joyent.com>

1 files changed, 39 insertions, 5 deletions

diff --git a/man/man1m/zfs.1m b/man/man1m/zfs.1m
index 6d5ca9efff9e..c24db19a2df4 100644
--- a/man/man1m/zfs.1m
+++ b/man/man1m/zfs.1m
@@ -27,6 +27,7 @@
 .\" Copyright (c) 2014 by Adam Stevko. All rights reserved.
 .\" Copyright (c) 2014 Integros [integros.com]
 .\" Copyright 2017 Nexenta Systems, Inc.
+.\" Copyright 2018 Joyent, Inc.
 .\"
 .Dd December 6, 2017
 .Dt ZFS 1M
@@ -1345,7 +1346,7 @@ Limits the amount of space a dataset can consume.
 This property enforces a hard limit on the amount of space used.
 This hard limit does not include space used by descendents, including file
 systems and snapshots.
-.It Sy refreservation Ns = Ns Em size Ns | Ns Sy none
+.It Sy refreservation Ns = Ns Em size Ns | Ns Sy none Ns | Ns Sy auto
 The minimum amount of space guaranteed to a dataset, not including its
 descendents.
 When the amount of space used is below this value, the dataset is treated as if
@@ -1363,6 +1364,22 @@ this reservation to accommodate the current number of
 .Qq referenced
 bytes in the dataset.
 .Pp
+If
+.Sy refreservation
+is set to
+.Sy auto ,
+a volume is thick provisioned
+.Po or
+.Qq not sparse
+.Pc .
+.Sy refreservation Ns = Ns Sy auto
+is only supported on volumes.
+See
+.Sy volsize
+in the
+.Sx Native Properties
+section for more information about sparse volumes.
+.Pp
 This property can also be referred to by its shortened column name,
 .Sy refreserv .
 .It Sy reservation Ns = Ns Em size Ns | Ns Sy none
@@ -1577,22 +1594,39 @@ Extreme care should be used when adjusting the volume size.
 Though not recommended, a
 .Qq sparse volume
 .Po also known as
-.Qq thin provisioning
+.Qq thin provisioned
 .Pc
 can be created by specifying the
 .Fl s
 option to the
 .Nm zfs Cm create Fl V
-command, or by changing the reservation after the volume has been created.
+command, or by changing the value of the
+.Sy refreservation
+property
+.Po or
+.Sy reservation
+property on pool version 8 or earlier
+.Pc
+after the volume has been created.
 A
 .Qq sparse volume
-is a volume where the reservation is less then the volume size.
+is a volume where the value of
+.Sy refreservation
+is less than the size of the volume plus the space required to store its
+metadata.
 Consequently, writes to a sparse volume can fail with
 .Er ENOSPC
 when the pool is low on space.
 For a sparse volume, changes to
 .Sy volsize
-are not reflected in the reservation.
+are not reflected in the
+.Sy refreservation.
+A volume that is not sparse is said to be
+.Qq thick provisioned .
+A sparse volume can become thick provisioned by setting
+.Sy refreservation
+to
+.Sy auto .
 .It Sy vscan Ns = Ns Sy on Ns | Ns Sy off
 Controls whether regular files should be scanned for viruses when a file is
 opened and closed.