Configuring block thin clones
About thin clones
A thin clone is a read-write copy of a thin block storage resource (LUN, consistency group, or VMFS datastore) that shares blocks with the parent resource. Data available on the source snapshot at the moment of the thin clone creation is immediately available to the thin clone. The thin clone references the source snapshot for this data. However, data resulting from changes to the thin clone after its creation is stored on the thin clone. Changes to the thin clone do not affect the source snapshot, because the source snapshot is read-only.
Advantages of using thin clonesThin clones allow you to create and manage space-efficient copies of production environments, which is beneficial for the following types of activities:
- Development and test environments - Thin clones allow development and test personnel to work with real workloads and use all data services associated with production storage resources without interfering with production. They also allow development personnel to promote a test thin clone to production.
- Parallel processing - Parallel processing applications that span multiple servers can use multiple thin clones of a single production data set to achieve results more quickly.
- Online backup - You can use thin clones to maintain hot backup copies of production systems. If there is corruption in the production data set, you can immediately resume the read-write workload by using the thin clones.
- System deployment - You can use thin clones to build and deploy templates for identical or near-identical environments. For example, you can create a test template that is cloned as needed for predictable testing.
Thin clone restrictions
The following restrictions apply to thin clones:
- Thin clones are not supported for snapshots of thick LUNs.
- When you create a thin clone, the source snapshot for the clone must be read-only, and it cannot have automatic snapshot deletion or a snapshot expiration policy enabled.
- After you create a thin clone, the source snapshot can be deleted.
- You cannot create a thin clone of a thin clone without first creating an intermediate snapshot.
- A thin clone becomes a full clone on the destination storage system when it is replicated.
- You cannot delete a base storage resource (production resource) when it has thin clones.
- You cannot move a thin clone.
Thin clone terminology and hierarchy
The snapshots and thin clones for a LUN, consistency group, or VMware VMFS datastore form a hierarchy. This document uses the following terms to describe this hierarchy:
- Source snapshot
A snapshot of a LUN, consistency group, or VMFS datastore used as the source for thin clone create and refresh operations.
- Base LUN, base consistency group, base VMFS datastore
The founding (production) LUN, LUN group, or VMFS datastore for a set of derivative snapshots and thin clones.
- Base LUN family, base consistency group family, base VMFS datastore family
A LUN, consistency group, or base VMFS datastore and all of its derivative thin clones and snapshots. This includes snapshots and thin clones based on child snapshots of the storage resource or its thin clones, and so forth.
- Original parent resource
The original parent datastore or thin clone for the snapshot on which the thin clone is based. This resource does not change when a thin clone is refreshed to a different source snapshot, because the new source snapshot must be in the same base LUN, consistency group, or VMFS datastore family.
For example, suppose the following hierarchy of snapshots and thin clones exists for LUN 1:
The base LUN family for LUN 1 includes all of the snapshots and thin clones shown in the diagram.
For Thin Clone 2:
- The source snapshot is Snapshot 2.
- The base resource is LUN 1.
- The original parent resource is LUN 1.
For Thin Clone 3:
- The source snapshot is Snapshot 3.
- The base resource is LUN 1.
- The original parent resource is Thin Clone 2.
Now, if Thin Clone 3 is refreshed to Snapshot 1:
- The source snapshot changes from Snapshot 3 to Snapshot 1.
- The base resource is still LUN 1.
- The original parent resource is still Thin Clone 2.
If Thin Clone 2 is deleted after Thin Clone 3 is refreshed, the original parent resource shows as empty.
Create a thin clone
You can create thin clones for LUNs, consistency groups, and VMware VMFS datstores.
- Locate the summary page for the storage resource you want to clone.
- Select the storage resource, and then select .
- Select whether you want to create the thin clone from an existing or newly-created snapshot. To create the thin clone from an existing snapshot, select the snapshot.
- On the Configure page, specify the relevant information, and optionally select Create I/O Limit to create a new I/O limit policy for the thin clone.
- Continue following the steps in the wizard to optionally configure host access, a snapshot schedule, and replication for the thin clone. You can configure these features now or at a later time.
Change thin clone properties
- Locate the summary page for the storage resource associated with the thin clone you want to modify.
- Select the relevant thin clone, and then select the Edit icon.
- On the General tab, change the name, description, and size of the thin clone.
- On the Host Access tab, modify the list of hosts that have access to the thin clone, or change the type of access.
- On the FAST VP tab, view the data distribution per tier.
- On the Snapshots tab, manage the thin clone's snapshots or configure a snapshot schedule for the thin clone.
- On the Replication tab, configure replication settings. Select Configure Replication to get started.
- On the Host I/O Limit tab, view the bandwidth and throughput performance of the thin clone with the current policy, select a different policy and preview the performance impact of that policy, or apply a new policy.
Refresh a thin clone
Refreshing a thin clone updates the thin clone's data with data from a different source snapshot. The new source snapshot must belong to the thin clone family; that is, it must be related to the base LUN, base consistency group, or base VMware VMFS datastore for the existing thin clone. In addition, it must be read-only, and it cannot have automatic snapshot deletion or a snapshot expiration policy enabled.
When you refresh a thin clone, the existing data is removed from the thin clone and the data from the new source snapshot is copied to it. If the thin clone has derivative snapshots, they remain unchanged, and the family hierarchy stays intact.
Note: You can promote a test thin clone to production by refreshing the base storage resource with the thin clone's snapshot. This provides the ability to refresh production environments based on factors such as performance tuning, query optimization, and bug fixes. It is strongly recommended to disable base the base LUN's host access before this performing this operation.
- Locate the summary page for the source storage resource whose thin clone you want to refresh.
- Select the relevant thin clone, and then select .
- Select whether you wan create a snapshot of thin clone before it refreshes.
Note: It is recommended that you leave the default, which is to have the system create a copy of the thin clone before refreshing.
- Select the source snapshot for the refresh.