System Administration Guide: Basic Administration

Creating and Deleting UFS Snapshots

When you use the fssnap command to create a UFS 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 –

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.

For more information, see fssnap_ufs(1M).

How to Create a UFS Snapshot

Become superuser or assume an equivalent role.

Make sure that the file system has enough disk space for the backing-store file.
# df -k

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

Create the UFS snapshot.
# fssnap -F ufs -o bs=/backing-store-file /file-system
Note –
The backing-store file must reside on a different file system than the file system that is being snapshot.

Verify that the snapshot has been created.

# /usr/lib/fs/ufs/fssnap -i /file-system

Examples—Creating a UFS Snapshot

The following example shows how to create 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 shows how to limit 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 UFS snapshots and their corresponding virtual devices.

Note –

Use the UFS file system-specific fssnap command to view the extended snapshot information as shown in the following examples.

Become superuser or assume an equivalent role.

List current snapshots.

# /usr/lib/fs/ufs/fssnap -i
Snapshot number               : 0
Block Device                  : /dev/fssnap/0
Raw Device                    : /dev/rfssnap/0
Mount point                   : /export/home
Device state                  : idle
Backing store path            : /var/tmp/bs.file
Backing store size            : 0 KB
Maximum backing store size    : Unlimited
Snapshot create time          : Wed Aug 29 15:22:06 2001
Copy-on-write granularity     : 32 KB

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

# /usr/lib/fs/ufs/fssnap -i /usr
Snapshot number               : 0
Block Device                  : /dev/fssnap/0
Raw Device                    : /dev/rfssnap/0
Mount point                   : /usr
Device state                  : idle
Backing store path            : /var/tmp/bs.file
Backing store size            : 0 KB
Maximum backing store size    : Unlimited
Snapshot create time          : Wed Aug 29 15:23:35 2001
Copy-on-write granularity     : 32 KB

Deleting a UFS Snapshot

When you create a UFS snapshot, you can specify that the backing-store file is unlinked, which means that the backing-store file is removed after the snapshot is deleted. If you don't specify the -o unlink option when you create a UFS snapshot, you will have to delete it manually.

The backing-store file occupies disk space until the snapshot is deleted, whether you use the -o unlink option to remove the backing-store file or you remove it manually.

How to Delete a UFS Snapshot

You can delete a snapshot either by rebooting the system or by using the fssnap -d command and specifying the path of the file system that contains the UFS snapshot.

Become superuser or assume an equivalent role.

Identify the snapshot to be deleted.
# /usr/lib/fs/ufs/fssnap -i

Delete the snapshot.

# fssnap -d /file-system
Deleted snapshot 1.

(Optional) If you did not use the -o unlink option when you created the snapshot, you need to delete the backing-store file manually.
# rm /file-system/backing-store-file

Example—Deleting a UFS Snapshot

The following example shows how to delete a snapshot and assumes that the unlink option was not used.

# fssnap -i
    0    /    1    /usr
# fssnap -d /usr
 Deleted snapshot 1.
# rm /scratch/usr.back.file