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Solaris 8 System Administration Supplement

Creating UFS Snapshots

When you use the fssnap command to create a file-system snapshot, observe how much disk space the backing-store file consumes. The backing-store file uses no space, and then it grows quickly, especially on heavily used systems. Make sure the backing-store file has enough space to grow, or limit its size with the -o maxsize=n [k,m,g] option, where n [k,m,g] is the maximum size of the backing-store file.

Caution – Caution –

If the backing-store file runs out of space, the snapshot might delete itself, which causes the backup to fail. Check the /var/adm/messages file for possible snapshot errors.

How to Create a UFS Snapshot

  1. Become superuser.

  2. Make sure that the file system has enough disk space for the backing-store file.


    # df -k

  3. Make sure that a backing-store file of the same name and location does not already exist.


    # ls /file-system/backing-store-file

  4. Create the file-system snapshot.


    # fssnap -F ufs -o bs=/file-system/backing-store-file /file-system

Examples—Creating a UFS Snapshot

The following example creates a snapshot of the /usr file system. The backing-store file is /scratch/usr.back.file, and the virtual device is /dev/fssnap/1.


# fssnap -F ufs -o bs=/scratch/usr.back.file /usr
/dev/fssnap/1

The following example limits the backing-store file to 500 Mbytes.


# fssnap -F ufs -o maxsize=500m,bs=/scratch/usr.back.file /export/home 
/dev/fssnap/1

How to Display UFS Snapshot Information

You can display the current snapshots on the system by using the fssnap -i option. If you specify a file system, you see detailed information about that snapshot. If you don't specify a file system, you see information about all of the current file-system snapshots and their corresponding virtual devices.

  1. Become superuser.

  2. List current snapshots.


    # fssnap -i
   0    /
   1    /usr

    To display detailed information about a specific snapshot, use the following:


    # fssnap -i /usr
Snapshot number               : 1
Block Device                  : /dev/fssnap/1
Raw Device                    : /dev/rfssnap/1
Mount point                   : /usr
Device state                  : idle
Backing store path            : /scratch/usr.back.file
Backing store size            : 480 KB
Maximum backing store size    : Unlimited
Snapshot create time          : Tue Aug 08 09:57:07 2000
Copy-on-write granularity     : 32 KB