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VSS stands for "Volume Shadow Copy Service". Unlike virtual machine
snapshot, it only takes snapshot for the virtual disks, so both
filesystem and applications have to aware of it, and cooperate the
whole VSS process.
This driver exposes two device files to the userland:
/dev/hv_fsvss_dev
Normally userland programs should _not_ mess with this device file.
It is currently used by the hv_vss_daemon(8), which freezes and
thaws the filesystem. NOTE: currently only UFS is supported, if
the system mounts _any_ other filesystems, the hv_vss_daemon(8)
will veto the VSS process.
If hv_vss_daemon(8) was disabled, then this device file must be
opened, and proper ioctls must be issued to keep the VSS working.
/dev/hv_appvss_dev
Userland application can opened this device file to receive the
VSS freeze notification, hold the VSS for a while (mainly to flush
application data to filesystem), release the VSS process, and
receive the VSS thaw notification i.e. applications can run again.
The VSS will still work, even if this device file is not opened.
However, only filesystem consistency is promised, if this device
file is not opened or is not operated properly.
hv_vss_daemon(8) is started by devd(8) by default. It can be disabled
by editting /etc/devd/hyperv.conf.
Submitted by: Hongjiang Zhang <honzhan microsoft com>
Reviewed by: kib, mckusick
MFC after: 3 weeks
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D8224
89 lines
2.8 KiB
Groff
89 lines
2.8 KiB
Groff
.\" Copyright (c) 2016 Microsoft Corp.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.Dd October 12, 2016
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.Dt HV_VSS_DAEMON 8
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.Os
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.Sh NAME
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.Nm hv_vss_daemon
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.Nd Hyper-V Volume Shadow Copy Service Daemon
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.Sh SYNOPSIS
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.Nm
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.Op Fl dn
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.Sh DESCRIPTION
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The
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.Nm
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daemon provides the ability to freeze and thaw the file system for
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.Fx
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guest partitions running on Hyper-V.
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.Pp
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Hyper-V allows administrators to backup or restore the
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.Fx
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guest partition.
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Administrators can
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use Windows Powershell scripts to backup or restore the
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.Fx
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VM.
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.Pp
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The
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.Nm
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accepts file system freeze and thaw requests from the
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.Xr hv_utils 4
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driver and performs the actual file-system operation.
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.Pp
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The file system freeze and thaw functionality is
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useful when the Hyper-V host wants to do live backup of
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.Fx
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guest. Hyper-V host sends file system freezing request to
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.Nm
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which conducts the real operation. After successfully freezing file
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system, Hyper-V host takes a snapshot of the VM. In the future,
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Hyper-V host can restore the
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.Fx
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VM through that snapshot.
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.Pp
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The options are as follows:
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.Bl -tag -width indent
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.It Fl d
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Run as regular process instead of a daemon for debugging purpose.
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.It Fl n
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Generate debugging output.
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.El
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.Sh SEE ALSO
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.Xr hv_vmbus 4 ,
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.Xr hv_utils 4 ,
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.Xr hv_netvsc 4 ,
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.Xr hv_storvsc 4 ,
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.Xr hv_kvp 4
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.Sh HISTORY
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The daemon was introduced in October 2016 and developed by Microsoft Corp.
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.Sh AUTHORS
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.An -nosplit
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.Fx
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support for
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.Nm
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was first added by
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.An Microsoft BSD Integration Services Team Aq Mt bsdic@microsoft.com .
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