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FAQ - FlexClone split

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Applies to

  • ONTAP 9.3 and earlier
  • Data ONTAP 8.2 7-Mode
  • Clustered Data ONTAP 8.3

Answer

The following are frequently asked questions regarding splitting FlexClone volumes.

What is a FlexClone split?

A FlexClone split is the act of splitting a FlexClone volume from its parent volume. The split results in a full copy of all the shared data from the parent volume, and removes any relationship or dependency between the two volumes. After the split is complete, the FlexClone volume is no longer a FlexClone volume but a regular volume instead. It is not possible to choose a destination aggregate for a FlexClone split; it will always be the same aggregate as the parent volume.

How does Data ONTAP process a FlexClone split operation?

Data ONTAP uses a background scanner to copy the shared data from the parent volume to the FlexClone volume. The scanner has one active message at any time that is processing only one inode, so the split tends to be faster on a volume with fewer inodes. Also, any data written, overwritten, or deleted on the FlexClone volume will not be shared with the parent volume and thus does not need to be copied. During the split operation, both the parent and FlexClone volumes are online and the operation is non-disruptive to client access.

Are there any special considerations for using FlexClone split?

Splitting a FlexClone volume will result in all the snapshot copies on the FlexClone being deleted and will prevent any new snapshots on the FlexClone volume until the split completes. The FlexClone split operation is processed by a background scanner at a low priority and can take a considerable amount of time to complete. FlexVols with many inodes (files) will process slower than FlexVols with few inodes (files).

Is there an alternative for a FlexClone split that retains the snapshots in the FlexClone volume?

If using Data ONTAP in Cluster-Mode, a functional equivalent to a FlexClone split is to perform a volume move of the FlexClone volume. The volume move will result in a full copy of all the data from the FlexClone (and thus, the parent volume for the shared blocks) to a different aggregate. After the volume move operation completes, any relationship or dependencies are released and the FlexClone volume becomes a regular volume. Volume move preserves all the snapshots, and during the move, new snapshots can be created. The volume move speed observed for a FlexClone volume is similar to that of a normal volume and is non-disruptive to client access. A volume move operation will typically require more freespace during processing than a FlexClone split operation, because all the data (shared and non-shared) is copied, whereas in a FlexClone split only the shared data is copied.

If using Data ONTAP in 7-Mode use the vol copy command or SnapMirror to create the initial full copy.

How much capacity is required to perform a FlexClone split operation?

Immediately after the creation of a FlexClone volume, all data is shared between it and the reference snapshot of the parent volume, and splitting the FlexClone volume from the parent volume would require a storage capacity equal to the used capacity of the parent active filesystem at the time of the snapshot. As the FlexClone volume and the parent diverge due to writes, overwrites, and deletions, the amount of shared data decreases. Data ONTAP includes a command that estimates the amount of storage capacity required to split a FlexClone volume from its parent.

Note:  Beginning with ONTAP 9.4, for non-guaranteed volumes on AFF systems, the split operation for FlexClone volumes shares the physical blocks and does not copy the data.

  • For Data ONTAP in Cluster-Mode, use the volume clone split estimate command. The following is a sample usage and output of this command.

c-mode::> volume clone split estimate
Split
Vserver FlexClone Estimate
--------- ------------- ----------
demo10-vs1
quotas_c 8.55GB

  • For Data ONTAP in 7-Mode, use the vol clone split estimate command. The following is a sample usage and output of this command.

7-mode> vol clone split estimate quotas_c
An estimated 10gb available storage is required in the aggregate to split
clone volume 'quotas_c' from its parent.

How do you monitor the progress of a FlexClone split?

  • For Data ONTAP in Cluster-Mode, use the volume clone split status command. The following is a sample usage and output of this command.

c-mode::> volume clone split status
Inodes Blocks
--------------------- ---------------------
Vserver FlexClone Processed Total Scanned Updated % Complete
--------- ------------- ---------- ---------- ---------- ---------- ----------
demo10-vs1
quotas_c 98007 3309579 354217 293763 2

  • For Data ONTAP in 7-Mode, use the vol clone split status command. The following is a sample usage and output of this command.

7-mode> vol clone split status
Volume 'quotas_c', 108175 of 2912700 inodes processed (3%)
251788 blocks scanned. 239605 blocks updated.

Included in the output is a % complete or processed field. This field is based on the count of the inodes split, rather than the count of the blocks split. The value is a whole number and rounded down. If the volume contains a few large files or LUNs, the % field might not be an accurate representation of progress.

Why does a FlexVol clone split take a long time?

Clone-splitting operation in general might take considerable time to carry.

The flex clone split has to transfer every bit of data and free inode, to the volume that is being cloned. Hence, when a split is done, the total number of inodes displayed is used plus free, and each is copied to the volume that is being split and separated from the source.
The clone-splitting operation is a copy operation that might take considerable time and resources to carry out because of the following reasons:

  • Free blocks in the aggregate are used to copy blocks shared between the parent and the clone.
  • FlexClone splitting incurs disk I/O operations and can potentially compete with other disk operations in the aggregate.
  • Copy operation uses some CPU and memory resources, which may impact the performance of a fully loaded filer.

However, Data ONTAP addresses the potential performance impact of Split operation. The Split operation runs in the background, and priorities are set in such a way that it does not significantly impact foreground operations.
The clone operation proceeds in the background and does not interfere with data access to either the parent or the clone volume. Also, the user processes are not affected during the operation and the split operation is treated as a low priority job. This is not like a volume copy operation that copies only the data written in the volume.

If you create a clone volume, you can immediately start to use it and allow the split to occur in the background without impact to the data integrity (other than the fact that a snapshot cannot occur until the split completes). For more information about Cloning Flexible volumes and FlexClone splits, refer to the below documents:

Data ONTAP 8.2 7-Mode Storage Management Guide
Cluster Data ONTAP 8.3 Logical Storage Management Guide
Cluster Data ONTAP 9.x Logical Storage Management Guide

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