Cloning FlexVol volumes

What clones volumes are

Clone volumes are writable, point-in-time copy of a parent FlexVol volume. They reside in the same aggregate as their parent volume. Changes made to the parent volume after the clone is created are not inherited by the clone.

Because clone volumes and parent volumes share the same disk space for any data common to both, creating a clone is instantaneous and requires no additional disk space. You can split the clone from its parent if you do not want the clone and parent to share disk space.

Clone volumes are fully functional volumes; you manage them using the vol command, just as you do the parent volume. Clone volumes themselves can be cloned.

Reasons to clone FlexVol volumes

You can clone FlexVol volumes when you want a writable, point-in-time copy of a FlexVol volume. For example, you might want to clone FlexVol volumes in the following scenarios:

You need to create a temporary copy of a volume for testing or staging purposes.
You want to create multiple copies of data for additional users without giving them access to production data.
You want to copy a database for manipulation or projection operations without altering the original data.

How clone volumes affect LUNs

When you create clone volumes, LUNs in the parent volume are present in the clone but they are not mapped and they are offline. To bring the LUNs in the clone online, you must map them to igroups. When the LUNs in the parent volume are backed by Snapshot copies, the clone also inherits the Snapshot copies.

You can also clone individual LUNs. If the parent volume has LUN clones, the clone volume inherits the LUN clones. A LUN clone has a base Snapshot copy, which is also inherited by the volume clone. The LUN clone's base Snapshot copy in the parent volume shares blocks with the LUN clone's base Snapshot copy in the volume clone. You cannot delete the LUN clone's base Snapshot copy in the parent volume until you delete the base Snapshot copy in the volume clone.

How volume cloning affects space reservation

Volume-level guarantees

Clone volumes inherit the same volume-level space guarantee setting as the parent volume, but the space guarantee is disabled for the clone. This means that the containing aggregate does not ensure that space is always available for write operations to the clone volume, regardless of the clone's guarantee setting.

The following example shows guarantee settings for two volumes: a parent volume called testvol and its clone, testvol_c. For testvol the guarantee option is set to volume. For testvol_c, the guarantee option is set to volume, but the guarantee is disabled.

filer_1> vol options testvol

nosnap=off, nosnapdir=off, minra=off, no_atime_update=off, 
nvfail=off, snapmirrored=off, create_ucode=off, convert_ucode=off, 
maxdirsize=5242, fs_size_fixed=off, guarantee=volume, 
svo_enable=off, svo_checksum=off, svo_allow_rman=off, 
svo_reject_errors=off, fractional_reserve=100

filer_1> vol status testvol_c

Volume State      Status            Options

c1     online     raid_dp, flex     maxdirsize=5242,

                                    guarantee=volume(disabled)

       Clone, backed by volume 'testvol', snapshot 'hourly.0'

       Containing aggregate: 'a1'

Volume-level space guarantees are enabled on the clone volume only after you split the clone volume from its parent. After the clone-splitting process, space guarantees are enabled for the clone volume, but the guarantees are enforced only if there is enough space in the containing aggregate.

Space reservation and fractional overwrite reserve

LUNs in clone volumes inherit the space reservation setting from the LUNs in the parent volume. This means if space reservation is enabled for a LUN in the parent volume, it is also enabled for the LUN in the clone volume. Clone volumes inherit fractional overwrite reserve settings from the parent volume. For example, if fractional overwrite is set to 50 percent on the parent volume, it is also set to 50 percent on the clone volume. Space reservation and fractional overwrite reserve settings are enabled, but they are enforced only if there is enough space in the containing aggregate.

Commands for cloning FlexVol volumes

You use the following commands to clone FlexVol volumes:

vol clone create--creates a volume clone and a base Snapshot copy of the parent volume.
vol clone split--splits the volume clone from the parent so that they no longer share data blocks.

Cloning a FlexVol volume

To clone a FlexVol volume, complete the following steps.

Step	Action
1	Enter the following command to clone the volume: *vol clone create cl_vol_name* [-s {volume\|file\|none}] -b f_p_vol_name [parent_snap]** cl_vol_name is the name of the clone volume that you want to create. `-s {volume \| file \| none}` specifies the space guarantee for the new volume clone. If no value is specified, the clone is given the same space guarantee setting as its parent. For more information, see How volume cloning affects space reservation. Note For Data ONTAP 7.0, space guarantees are disabled for clone volumes until they are split from the parent volume. f_p_vol_name is the name of the flexible parent volume that you intend to clone. [parent_snap] is the name of the base Snapshot copy of the parent volume. If no name is specified, Data ONTAP creates a base Snapshot copy with the name clone_cl_name_prefix.id, where cl_name_prefix is the name of the new clone volume (up to 16 characters) and id is a unique digit identifier (for example 1,2, and so on). The base Snapshot copy cannot be deleted as long as the parent volume or any of its clones exists. Example Snapshot copy name: To create a clone newclone of the volume named flexvol1, the following command is entered: `vol clone create newclone -b flexvol1` The Snapshot copy created by Data ONTAP is named clone_newclone.1.
2	Verify the success of the clone creation by entering the following command: vol status -v cl_vol_name

Step

Action

Enter the following command to clone the volume:

vol clone create cl_vol_name [-s {volume|file|none}] -b 
f_p_vol_name [parent_snap]

cl_vol_name is the name of the clone volume that you want to create.

-s {volume | file | none} specifies the space guarantee for the new volume clone. If no value is specified, the clone is given the same space guarantee setting as its parent. For more information, see How volume cloning affects space reservation.

Note
For Data ONTAP 7.0, space guarantees are disabled for clone volumes until they are split from the parent volume.

f_p_vol_name is the name of the flexible parent volume that you intend to clone.

[parent_snap] is the name of the base Snapshot copy of the parent volume. If no name is specified, Data ONTAP creates a base Snapshot copy with the name clone_cl_name_prefix.id, where cl_name_prefix is the name of the new clone volume (up to 16 characters) and id is a unique digit identifier (for example 1,2, and so on).

The base Snapshot copy cannot be deleted as long as the parent volume or any of its clones exists.

Example Snapshot copy name:

To create a clone newclone of the volume named flexvol1, the following command is entered:

vol clone create newclone -b flexvol1

The Snapshot copy created by Data ONTAP is named clone_newclone.1.

Verify the success of the clone creation by entering the following command:

vol status -v cl_vol_name

Splitting a cloned volume

You might want to split your cloned volume into two independent volumes that occupy their own disk space.

Note
Because the clone-splitting operation is a copy operation that might take considerable time to carry out, Data ONTAP also provides commands to stop or check the status of a clone-splitting operation.

If you take the clone offline while the splitting operation is in progress, the operation is suspended; when you bring the clone back online, the splitting operation resumes.

To split a clone from its parent volume, complete the following steps.

Step	Action
1	Verify that enough additional disk space exists in the containing aggregate to support the clone and its parent volume unsharing their shared disk space by entering the following command: df -A aggr_name aggr_name is the name of the containing aggregate of the FlexVol volume clone that you want to split. The `avail` column tells you how much available space you have in your aggregate. When a volume clone is split from its parent, the resulting two FlexVol volumes occupy completely different blocks within the same aggregate.
2	Enter the following command to split the volume: vol clone split start cl_vol_name cl_vol_name is the name of the clone that you want to split from its parent. The original volume and its clone begin to split apart, unsharing the blocks that they formerly shared.
3	If you want to check the status of a clone-splitting operation, enter the following command: vol clone status cl_vol_name
4	If you want to stop the progress of an ongoing clone-splitting operation, enter the following command: vol clone stop cl_vol_name The clone-splitting operation halts; the original and clone volumes will remain clone partners, but the disk space that was duplicated up to that point will remain duplicated.
5	Display status for the newly split volume to verify the success of the clone-splitting operation by entering the following command: vol status -v cl_vol_name

For detailed information

For detailed information about volume cloning, including limitations of volume cloning, see the Data ONTAP Storage Management Guide.