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Warn user about accidentally sharing devices 

Improve the man page text to warn the user about the risk of adding
the same device to multiple pools via simultaneous "zpool create",
"zpool add", "zpool replace", etc.

State that MMP/multihost does not protect against these scenarios.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #6473 
Closes #8457
This commit is contained in:
Olaf Faaland 2019-02-28 17:54:36 -08:00 committed by Brian Behlendorf
parent 87c25d567f
commit 4f3218aed8
1 changed files with 30 additions and 5 deletions
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35
man/man8/zpool.8
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@ -442,6 +442,11 @@ If a pool has a shared spare that is currently being used, the pool can not be
exported since other pools may use this shared spare, which may lead to
potential data corruption.
.Pp
Shared spares add some risk. If the pools are imported on different hosts, and
both pools suffer a device failure at the same time, both could attempt to use
the spare at the same time. This may not be detected, resulting in data
corruption.
.Pp
An in-progress spare replacement can be cancelled by detaching the hot spare.
If the original faulted device is detached, then the hot spare assumes its
place in the configuration, and is removed from the spare list of all active
@ -829,9 +834,15 @@ Controls whether a pool activity check should be performed during
When a pool is determined to be active it cannot be imported, even with the
.Fl f
option. This property is intended to be used in failover configurations
where multiple hosts have access to a pool on shared storage. When this
property is on, periodic writes to storage occur to show the pool is in use.
See
where multiple hosts have access to a pool on shared storage.
Multihost provides protection on import only. It does not protect against an
individual device being used in multiple pools, regardless of the type of vdev.
See the discussion under
.Sy zpool create.
When this property is on, periodic writes to storage occur to show the pool is
in use. See
.Sy zfs_multihost_interval
in the
.Xr zfs-module-parameters 5
@ -1045,8 +1056,22 @@ specification is described in the
.Sx Virtual Devices
section.
.Pp
The command verifies that each device specified is accessible and not currently
in use by another subsystem.
The command attempts to verify that each device specified is accessible and not
currently in use by another subsystem. However this check is not robust enough
to detect simultaneous attempts to use a new device in different pools, even if
.Sy multihost
is
.Sy enabled.
The
administrator must ensure that simultaneous invocations of any combination of
.Sy zpool replace ,
.Sy zpool create ,
.Sy zpool add ,
or
.Sy zpool labelclear ,
do not refer to the same device. Using the same device in two pools will
result in pool corruption.
There are some uses, such as being currently mounted, or specified as the
dedicated dump device, that prevents a device from ever being used by ZFS.
Other uses, such as having a preexisting UFS file system, can be overridden with