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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.
Pp
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.
Pp
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.
Pp
Options indicate an action to be performed:
Bl -tag -width 3n
It 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.
It 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.
It Fl u
Unconfigures the
Ar device .
It Fl v
Be more verbose listing the snapshot devices.
It Fl x
Unlink
Ar backup
after the
Ar device
is configured.
El
Pp
If no action option is given,
Fl c
is assumed.
Sh FILES
Bl -tag -width /etc/disktab -compact
It Pa /dev/rfss?
It Pa /dev/fss?
El
Sh EXAMPLES
Dl fssconfig fss0 /usr /tmp/back
Dl mount /dev/fss0 /mnt
Pp
Configures the snapshot device
Pa fss0
as a snapshot of the
Pa /usr
file system, and makes the contents of the snapshot available via
Pa /mnt .
Data written through
Pa /usr
will be backed up in
Pa /tmp/back .
Pp
Dl fssconfig fss1 / /dev/rsd0e 8192
Pp
Configures the snapshot device
Pa fss1
as a snapshot of the
Pa /
file system.
Data written through
Pa /
will be backed up in
Pa /dev/rsd0e .
The backup will take place in units of 8192 bytes.
Pp
Dl fssconfig -u fss0
Pp
Unconfigures the
Pa 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 .

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