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 $NetBSD: fssconfig.8,v 1.12 2016/07/29 05:20:33 pgoyette Exp $ */


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 This code is derived from software contributed to The NetBSD Foundation
 by Juergen Hannken-Illjes.

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.Dd July 29, 2016
.Dt FSSCONFIG 8
.Os
.Sh NAME
.Nm fssconfig
.Nd configure file system snapshot devices
.Sh SYNOPSIS
.Nm
.Op Fl cxv
.Ar device
.Ar path
.Ar backup
.Op Ar cluster Op Ar size
.Nm
.Fl u Op Fl v
.Ar device
.Nm
.Fl l Op Fl v
.Op Ar device
.Sh DESCRIPTION
The
.Nm
command configures file system snapshot pseudo disk devices.
It will associate the file system snapshot disk
.Ar device
with a snapshot of the file system mounted on
.Ar path ,
allowing
.Ar device
to be accessed as though it were a disk.

p
If
.Ar backup
resides on the snapshotted file system a persistent snapshot will be created.
This snapshot is active until
.Ar backup
is unlinked.
Persistent snapshots save the file system as if it had been unmounted.
Unlinked but open files get removed from the snapshot.
The time needed to create a persistent snapshot increases with the size of the
file system and decreases with the file system block size.
This snapshot mode is only supported for FFS file systems.

p
Otherwise data written through the
.Ar path
will be saved in
.Ar backup .
If
.Ar backup
is a regular file, it will be created with length
.Ar size .
Default size is the size of
.Ar path .
Data is saved to
.Ar backup
in units of
.Ar cluster
bytes.
The snapshot is an image of the underlying block device at a moment in time.
Unlinked but open files are still present on the snapshot.
The time needed to create a snapshot is independent of the size of the
file system or the file system block size.

p
Options indicate an action to be performed:
l -tag -width 3n t Fl c Configures the device.
If successful, references to
.Ar device
will access the contents of
.Ar path
at the time the snapshot was taken.
If
.Ar backup
is a directory, a temporary file will be created in this directory.
This file will be unlinked on exit.
t Fl l List the snapshot devices and indicate which ones are in use.
If a specific
.Ar device
is given, then only that will be described.
t Fl u Unconfigures the
.Ar device .
t Fl v Be more verbose listing the snapshot devices.
t Fl x Unlink
.Ar backup
after the
.Ar device
is configured.
.El

p
If no action option is given,
.Fl c
is assumed.
.Sh FILES
l -tag -width /etc/disktab -compact t Pa /dev/rfss? t Pa /dev/fss? .El
.Sh EXAMPLES
.Dl fssconfig fss0 /usr /tmp/back
.Dl mount /dev/fss0 /mnt

p
Configures the snapshot device

a fss0
as a snapshot of the

a /usr
file system, and makes the contents of the snapshot available via

a /mnt .
Data written through

a /usr
will be backed up in

a /tmp/back .

p
.Dl fssconfig fss1 / /dev/rsd0e 8192

p
Configures the snapshot device

a fss1
as a snapshot of the

a /
file system.
Data written through

a /
will be backed up in

a /dev/rsd0e .
The backup will take place in units of 8192 bytes.

p
.Dl fssconfig -u fss0

p
Unconfigures the

a fss0
device.
.Sh SEE ALSO
.Xr opendisk 3 ,
.Xr fss 4 ,
.Xr dump 8 ,
.Xr mount 8 ,
.Xr umount 8
.Sh HISTORY
The
.Nm
command appeared in
.Nx 2.0 .