fssnap_ufs man page on SmartOS

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       fssnap_ufs - create a temporary snapshot of a UFS file system

       fssnap [-F ufs] [-V] -o backing-store=path,
	    [specific-options] /mount/point

       fssnap -d [-F ufs] [-V] /mount/point | dev

       fssnap -i [-F ufs] [-V] [-o specific-options] /mount/point | dev

       The fssnap command queries, creates, or deletes a temporary snapshot of
       a UFS file system. A snapshot is a point-in-time image of a file system
       that provides a stable and unchanging device interface for backups.

       When  creating a file system snapshot, you must specify the file system
       to be captured and the backing-store file.  The	backing-store  file(s)
       are  where  the snapshot subsystem saves old file system data before it
       is overwritten. Beyond the first backing-store file,  fssnap  automati‐
       cally creates additional backing-store files on an as-needed basis.

       The  number  and size of the backing store files varies with the amount
       of activity in the file system. The destination path must  have	enough
       free  space  to	hold  the backing-store file(s). This location must be
       different from the file system that is being captured  in  a  snapshot.
       The  backing-store  file(s)  can	 reside	 on  any  type of file system,
       including another UFS file system or an NFS-mounted file system.

       The following options are supported:


	   Deletes the snapshot associated with the given file system.


	   Displays the state of one or all UFS snapshots. If a mount-point or
	   device  is  not specified, a list of all snapshots on the system is
	   displayed.  When a mount-point or  device  is  specified,  detailed
	   information	is  provided for the specified file system snapshot by

	   Use the -o options with the -i  option  to  specify	what  snapshot
	   information	is displayed. Since this feature is provided primarily
	   for use in scripts and on the command line, no labels are displayed
	   for	the data. Sizes are all in bytes, and the output is not inter‐
	   nationalized or localized. The information is displayed on one line
	   per	option.	 Unrecognized  options display a single ? on the line.
	   One line per option guarantees that there are the  same  number  of
	   lines as options specified and there is a one-to-one correspondence
	   between an output line and an option.

	   The following -o options display specific information for  a	 given
	   snapshot. See the EXAMPLES section for examples of how to use these


	       Display the snapshot number.


	       Display the block device path.


	       Display the raw device path.


	       Display the mount point of the master file system.


	       Display the state of the snapshot device.


	       Display the location of the first backing-store file  for  this
	       snapshot. If there are multiple backing-store files, subsequent
	       files have the same name as the first file, with	 the  suffixes
	       .2, .3, and so forth.


	       Display the sum of the sizes of the backing-store files.


	       Display	the  maxsize  value  specified	for  the backing-store


	       Display the time that the snapshot was created.


	       Display the copy-on-write granularity.

       -o specific-options

	   Without -d or -i, the default  action  is  to  create  a  snapshot.
	   Specify  the	 following  options  when  creating a snapshot. All of
	   these options are discretionary, except for the backing-store file,
	   which is required.


	       Uses  path  in  the creation of the backing-store file(s). path
	       must not reside on the file system that is being captured in  a
	       snapshot	 and must not be the name of an existing file. If path
	       is a directory, then a backing-store file is created within  it
	       using  a name that is generated automatically. If path is not a
	       directory and does not already exist, then a backing-store file
	       with  that name is created. If more than one backing-store file
	       is required, fssnap creates subsequent files automatically. The
	       second  and  subsequent	files  have the same name as the first
	       file, with suffixes of .2, .3, and so forth.

	       This option can be abbreviated as bf=path or bs=path.


	       Unlinks the backing-store file after the snapshot  is  created.
	       This option specifies that the backing-store file does not need
	       to be removed manually when the snapshot is deleted. This might
	       make  administration more difficult since the file is not visi‐
	       ble in the file system. If this option is  not  specified,  the
	       backing-store  files should be removed manually after the snap‐
	       shot is deleted.

	   chunksize=n [k,m,g]

	       Uses n for the chunk size. Chunk size is the granularity of the
	       data that is sent to the backing store.

	       Specify	chunksize  in  the following units: k for kilobytes, m
	       for megabytes, or g for gigabytes. By default,  chunk  size  is
	       four times the block size of the file system (typically 32k).


	       Does  not  allow	 the  sum  of  the  sizes of the backing-store
	       file(s) to exceed n, where n is the unit specified.  The	 snap‐
	       shot  is deleted automatically when the sum of the sizes of the
	       backing-store file(s) exceeds maxsize.

	       Specify maxsize in the following units: k for kilobytes, m  for
	       megabytes, or g for gigabytes.


	       Displays	 to standard output the name of the raw device instead
	       of the block device when	 a  snapshot  is  created.  The	 block
	       device  is printed by default (when raw is not specified). This
	       option makes it easier to embed fssnap commands in the  command
	       line  for  commands  that require the raw device instead.  Both
	       devices are always created. This option affects only  the  out‐

       The following operands are supported:


	   The directory where the file system resides.


	   The physical device for the file system, such as /dev/dsk/c0t0d0s7.

       Example 1 Creating a Snapshot of a File System

       The  following  example	creates a snapshot of a file system. The block
       special device created for the snapshot is /dev/fssnap/0.

	 # fssnap -F ufs -o backing-store=/var/tmp /export/home

       Example 2 Backing Up a File System Snapshot Without Having  To  Unmount
       the File System

       The following example backs up a file system snapshot without having to
       unmount the file system. Since ufsdump  requires	 the  path  to	a  raw
       device,	the  raw option is used. The /export/home file system snapshot
       is removed in the second command.

	 # ufsdump 0uf /dev/rmt/0 `fssnap -F ufs
	       -o raw,bs=/export/snap /export/home`
	 <output from ufsdump>
	 # fssnap -F ufs -d /export/home

       Example 3 Backing Up a File System

       When backing up a file system, do not  let  the	backing-store  file(s)
       exceed  400  Mbytes.  The  second command removes the /export/home file
       system snapshot.

	 # ufsdump 0uf /dev/rmt/0 `fssnap -F ufs
	       -o maxsize=400m,backing-store=/export/snap,raw
	 # fssnap -F ufs -d /export/home

       Example 4 Performing an Incremental Dump of a Snapshot

       The following example uses ufsdump to back up a snapshot of /var.  Note
       the use of the N option to ufsdump, which writes the name of the device
       being  dumped,  rather  than  the  name	of  the	 snapshot  device,  to
       /etc/dumpdates file. See ufsdump(1M) for details on the N flag.

	 # ufsdump lfNu /dev/rmt/0 /dev/rdsk/c0t3d0s2 `fssnap -F ufs
	 -o raw,bs=/export/scratch,unlink /var`

       Example 5 Finding Out What Snapshots Currently Exist

       The following command displays the currently existing snapshots.

	 # fssnap -i
	 0  /src
	 1  /export/home
	 <output continues>

       Example 6 Mounting a File System Snapshot

       The  following example creates a file system snapshot. After you create
       a file system snapshot, mount it on /tmp/mount for temporary  read-only

	 # fssnap -F ufs -o backing-store=/nfs/server/scratch /export/home
	 # mkdir /tmp/mount
	 # mount -F ufs -o ro /dev/fssnap/1 /tmp/mount

       Example	7  Creating  a File System Snapshot and Unlinking the Backing-
       store File

       The following example creates a file system snapshot  and  unlinks  the
       backing-store file. After creating a file system snapshot and unlinking
       the backing-store file, check the state of the snapshot.

	 # fssnap -o bs=/scratch,unlink /src
	 # fssnap -i /src
	 Snapshot number	       : 0
	 Block Device		       : /dev/fssnap/0
	 Raw Device		       : /dev/rfssnap/0
	 Mount point		       : /src
	 Device state		       : active
	 Backing store path	       : /scratch/snapshot2 <UNLINKED>
	 Backing store size	       : 192 KB
	 Maximum backing store size    : Unlimited
	 Snapshot create time	       : Sat May 06 10:55:11 2000
	 Copy-on-write granularity     : 32 KB

       Example 8 Displaying the Size and Location of the Backing-store File(s)
       and the Creation Time for the Snapshot

       The following example displays the size of the backing-store file(s) in
       bytes, the location of the backing store, and the creation time for the
       snapshot of the /test file system.

	 # fssnap -i -o backing-store-len,backing-store,createtime /test
	 Sat May 6 10:55:11 2000

       Note  that  if  there are multiple backing-store files stored in /snap‐
       shot2, they will have names of the form	file  (for  the	 first	file),
       file.1, file.2, and so forth.

       The following exit values are returned:


	   Successful completion.


	   An error occurred.

       The script-readable output mode is a stable interface that can be added
       to, but will not change. All other interfaces are subject to change.

       mlock(3C), attributes(5)

       See the ntpd man page, delivered in the SUNWntpu package (not  a	 SunOS
       man page).

       The  fssnap device files should be treated like a regular disk block or
       character device.

       The association between a file system and the snapshot is lost when the
       snapshot	 is deleted or the system reboots. Snapshot persistence across
       reboots is not currently supported.

       To avoid unnecessary performance impacts, perform the snapshot and sys‐
       tem backup when the system is least active.

       It  is  not  possible  to perform a snapshot of a file system if any of
       the following conditions are true:

	   o	  The file system is in use by system accounting

	   o	  The file system contains a local swap file

	   o	  The file system is used as backing store by  an  application
		  that	uses mlock(3C) to lock its pages. Typically, these are
		  real time applications, such as ntpd (delivered in the  SUN‐
		  Wntpu package).

       These  conditions  result in fssnap being unable to write lock the file
       system prior to performing the snapshot.

				 Jan 29, 2007			FSSNAP_UFS(1M)

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