Cloning FlexVol volumes

About cloning FlexVol volumes

Data ONTAP provides the ability to clone FlexVol volumes, creating FlexClone volumes. The following list outlines some key facts about FlexClone volumes that you should know:

You must install the license for the FlexClone feature before you can create FlexClone volumes.
FlexClone volumes are a point-in-time, writable copy of the parent volume. Changes made to the parent volume after the FlexClone volume is created are not reflected in the FlexClone volume.
FlexClone volumes are fully functional volumes; you manage them using the vol command, just as you do the parent volume.
FlexClone volumes always exist in the same aggregate as their parent volumes.
FlexClone volumes can themselves be cloned.
FlexClone volumes and their parent volumes share the same disk space for any data common to the clone and parent. This means that creating a FlexClone volume is instantaneous and requires no additional disk space (until changes are made to the clone or parent).
Because creating a FlexClone volume does not involve copying data, FlexClone volume creation is very fast.
A FlexClone volume is created with the same space guarantee as its parent.
For more information, see Space guarantees.
While a FlexClone volume exists, some operations on its parent are not allowed.
For more information about these restrictions, see Limitations of volume cloning.
If, at a later time, you decide you want to sever the connection between the parent and the clone, you can split the FlexClone volume. This removes all restrictions on the parent volume and enables the space guarantee on the FlexClone volume.
Attention
Splitting a FlexClone volume from its parent volume deletes all existing snapshots of the FlexClone volume.

For more information, see FlexClone volumes and space guarantees.
When a FlexClone volume is created, quotas are reset on the FlexClone volume, and any LUNs present in the parent volume are present in the FlexClone volume but are unmapped.
For more information about using volume cloning with LUNs, see your Block Access Management Guide.
Only FlexVol volumes can be cloned. To create a copy of a traditional volume, you must use the vol copy command, which creates a distinct copy with its own storage.

Uses of volume cloning

You can use volume cloning whenever you need a writable, point-in-time copy of an existing FlexVol volume, including the following scenarios:

You need to create a temporary copy of a volume for testing purposes.
You need to make a copy of your data available to additional users without giving them access to the production data.
You want to create a clone of a database for manipulation and projection operations, while preserving the original data in unaltered form.

Benefits of volume cloning versus volume copying

Volume cloning provides similar results to volume copying, but cloning offers some important advantages over volume copying:

Volume cloning is instantaneous, whereas volume copying can be time consuming.
If the original and cloned volumes share a large amount of identical data, considerable space is saved because the shared data is not duplicated between the volume and the clone.

Limitations of volume cloning

The following operations are not allowed on parent volumes or their clones.

You cannot delete the base snapshot in a parent volume while a FlexClone volume using that snapshot exists. The base snapshot is the snapshot that was used to create the FlexClone volume, and is marked busy, vclone in the parent volume.
You cannot perform a volume SnapRestore® operation on the parent volume using a snapshot that was taken before the base snapshot was taken.
You cannot destroy a parent volume if any clone of that volume exists.
You cannot clone a volume that has been taken offline, although you can take the parent volume offline after it has been cloned.
You cannot create a volume SnapMirror relationship or perform a vol copy command using a FlexClone volume or its parent as the destination volume.
For more information about using SnapMirror with FlexClone volumes, see Using volume SnapMirror replication with FlexClone volumes.

Cloning a FlexVol volume

To create a FlexClone volume by cloning a FlexVol volume, complete the following steps.

Step	Action
1	Ensure that you have the flex_clone license installed.
2	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 FlexClone volume that you want to create. `-s {volume \| file \| none}` specifies the space guarantee setting for the new FlexClone volume. If no value is specified, the FlexClone volume is given the same space guarantee setting as its parent. For more information, see Space guarantees. f_p_vol_name is the name of the FlexVol volume that you intend to clone. parent_snap is the name of the base snapshot of the parent FlexVol volume. If no name is specified, Data ONTAP creates a base snapshot with the name clone_cl_name_prefix.id, where cl_name_prefix is the name of the new FlexClone volume (up to 16 characters) and id is a unique digit identifier (for example 1,2, etc.). The base snapshot cannot be deleted as long as the parent volume or any of its clones exists. Result The FlexClone volume is created and, if NFS is in use, an entry is added to the /etc/export file for every entry found for the parent volume.
	Example snapshot name: To create a FlexClone volume "newclone" from the parent "flexvol1", the following command is entered: `vol clone create newclone -b flexvol1` The snapshot created by Data ONTAP is named "clone_newclone.1".
3	Verify the success of the FlexClone volume creation by entering the following command: vol status -v cl_vol_name

FlexClone volumes and space guarantees

A FlexClone volume inherits its initial space guarantee setting from its parent volume. For example, if you create a FlexClone volume from a parent volume with a space guarantee of volume, then the FlexClone volume's initial space guarantee will be volume as well. You can change the FlexClone volume's space guarantee at any time.

FlexClone volumes and shared snapshots

A newly created FlexClone volume uses the snapshots it shares with its parent volume to optimize its space requirements from the aggregate when applying space guarantees. This is important because you can delete the shared snapshots from the FlexClone volume, but doing so may increase the space requirements of the FlexClone volume in the aggregate if space guarantees are being used.

Example

Suppose you have a 100-MB FlexVol volume with a space guarantee of volume, with 70 MB used and 30 MB free, and you use that FlexVol volume as a parent volume for a new FlexClone volume. The new FlexClone volume has an initial space guarantee of volume, but it does not require a full 100 MB of space from the aggregate, as it would if you had copied the volume. Instead, the aggregate only needs to allocate 100 MB minus 70 MB or 30 MB of free space to the clone.

Now, suppose that you delete the base snapshot from the FlexClone volume. Now, the FlexClone volume can no longer optimize its space requirements, and the full 100 MB is required from the containing aggregate.

What to do if you are prevented from deleting a snapshot from a FlexClone volume

If you are prevented from deleting a snapshot from a FlexClone volume due to "insufficient space in the aggregate," it is because deleting that snapshot requires the allocation of more data than the aggregate currently has available. You can either increase the size of the aggregate, or change the space guarantee of the FlexClone volume.

Note
Before changing the space guarantee of the FlexClone volume, make sure you understand the effects of making such a change. For more information, see Space guarantees.

Identifying shared snapshots in FlexClone volumes

Snapshots that are shared between a FlexClone volume and its parent are not identified as such in the FlexClone volume. However, you can identify a shared snapshot by listing the snapshots in the parent volume. Any snapshot that appears as busy, vclone in the parent volume and is also present in the FlexClone volume is a shared snapshot.

Using volume SnapMirror replication with FlexClone volumes

Because both volume SnapMirror replication and FlexClone volumes rely on snapshots, there are some restrictions on how the two features can be used together.

Creating a volume SnapMirror relationship using an existing FlexClone volume or its parent

You can create a volume SnapMirror relationship using a FlexClone volume or its parent as the source volume. However, you cannot create a new volume SnapMirror relationship using either a FlexClone volume or its parent as the destination volume.

Creating a FlexClone volume from volumes currently in a SnapMirror relationship

You can create a FlexClone volume from a volume that is currently either the source or destination in an existing volume SnapMirror relationship. For example, you might want to create a FlexClone volume to create a writable copy of a SnapMirror destination volume without affecting the data in the SnapMirror source volume.

However, when you create the FlexClone volume, you might lock a snapshot that is used by SnapMirror. If that happens, SnapMirror stops replicating to the destination volume until the FlexClone volume is destroyed or split from its parent. You have two options for addressing this issue:

If your need for the FlexClone volume is temporary, and you can accept the temporary cessation of SnapMirror replication, you can create the FlexClone volume and either delete it or split it from its parent when possible. At that time, the SnapMirror replication will continue normally.
If you cannot accept the temporary cessation of SnapMirror replication, you can create a snapshot in the SnapMirror source volume, and then use that snapshot to create the FlexClone volume. (If you are creating the FlexClone volume from the destination volume, you must wait until that snapshot replicates to the SnapMirror destination volume.) This method allows you to create the clone without locking down a snapshot that is in use by SnapMirror.

About splitting a FlexClone volume from its parent volume

You might want to split your FlexClone volume and its parent into two independent volumes that occupy their own disk space.

Attention
When you split a FlexClone volume from its parent, all existing snapshots of the FlexClone volume are deleted.

Splitting a FlexClone volume from its parent will remove any space optimizations currently employed by the FlexClone volume. After the split, both the FlexClone volume and the parent volume will require the full space allocation determined by their space guarantees.

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.

The clone-splitting operation proceeds in the background and does not interfere with data access to either the parent or the clone volume.

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

Once a FlexClone volume and its parent volume have been split, they cannot be rejoined.

Splitting a FlexClone volume

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

Step	Action
1	Determine the approximate amount of free space required to split a FlexClone volume from its parent, enter the following command: vol clone split estimate clone_name
2	Verify that enough free space exists in the containing aggregate to support storing the data of both the FlexClone volume and its parent volume by entering the following command: df -A aggr_name aggr_name is the name of the containing aggregate of the FlexClone volume that you want to split. The `avail` column tells you how much available space you have in your aggregate. Note When a FlexClone volume is split from its parent, the resulting two FlexVol volumes occupy completely different blocks within the same aggregate.
3	Enter the following command to split the volume: vol clone split start cl_vol_name cl_vol_name is the name of the FlexClone volume that you want to split from its parent. Result The original volume and its clone begin to split apart, no longer sharing the blocks that they formerly shared. All existing snapshots of the FlexClone volume are deleted.
4	If you want to check the status of a clone-splitting operation, enter the following command: vol clone status cl_vol_name
5	If you want to stop the progress of an ongoing clone-splitting operation, enter the following command: vol clone stop cl_vol_name Result The clone-splitting operation halts; the original and FlexClone volumes remain clone partners, but the disk space that was duplicated up to that point remains duplicated. All existing snapshots of the FlexClone volume are deleted.
6	To display status for the newly split FlexVol volume and verify the success of the clone-splitting operation, enter the following command: vol status -v cl_vol_name

Cloning FlexVol volumes

About cloning FlexVol volumes

Uses of volume cloning

Benefits of volume cloning versus volume copying

Limitations of volume cloning

Cloning a FlexVol volume

Result

Example snapshot name:

FlexClone volumes and space guarantees

FlexClone volumes and shared snapshots

Example

What to do if you are prevented from deleting a snapshot from a FlexClone volume

Identifying shared snapshots in FlexClone volumes

Using volume SnapMirror replication with FlexClone volumes

Creating a volume SnapMirror relationship using an existing FlexClone volume or its parent

Creating a FlexClone volume from volumes currently in a SnapMirror relationship

About splitting a FlexClone volume from its parent volume

Splitting a FlexClone volume

Result

Result