ShadowImage enables the creation of in-system, RAID-protected, read/write, volume-consistent, full clones.
As with TI snapshots, consistent clones can be created using Consistency Groups (CTGs).
- Quick Split - copying from primary to secondary is performed in the background so that the secondary is immediately available for reading/writing. The performance of the primary may be affected if access the secondary references data that has not yet been copied from the primary. In this case, on-demand copying of that data from the primary is required.
- Steady Split - copying from primary to secondary is performed in the foreground before the secondary is made available for reading/writing. The creation of the secondary takes time depending on volume size.
If using Dynamic Provisioning (DP) volumes for both primary and secondary volumes, the copy is applied only for the allocated area; the unallocated area is ignored.
- Quick Resync - resynchronization is performed in the background and on-demand. The secondary is briefly made read only (for less than 1 second), after which it becomes available for reading/writing (i.e it enters the PAIR state in less than 1 second). The performance of the primary may be affected if access to the secondary requires on-demand resyncing from the primary.
- Normal Copy - the secondary is made unavailable while the resynchronization is performed. The resync takes time depending on the size of differentials between the primary and secondary.
- Steady Split and Normal Copy - the storage system presents the actual contents of the secondary volume. This is in contrast to TI snapshots, where a merging process is required between the primary and secondary volumes to reconstruct the data.
- Quick Split and Quick Resync - the storage system presents the actual contents of the secondary volume. However a merging process may be required between the primary and secondary volumes to reconstruct the accessed block of data, if the background copy of that block has not yet been performed.
The following table shows how Quick Split and Quick Resync (indicated by the suffix q) are affected by upstream and downstream operations in an SI data flow:
| Data Flow | Behaviour |
|---|---|
| SIq |
The SI is performed using quick operations. The SI secondary is immediately available for manually mounting. |
| SIq with auto-mount of secondary |
The SI is performed using quick operations. The SI secondary is auto-mounted immediately. |
| SIq with downstream replications/snapshots |
SI is performed using quick operations. However:
See note below. |
| SIq with auto-mount and downstream replications/snapshots |
SI is performed using quick operations. However:
See note below. |
| Upstream replications with downstream SIq |
SI is performed using quick operations. The SI secondary is immediately available for manually mounting. There is no impact on upstream replications. |
When the clone is deleted the storage system releases the bitmap.
Protector supports Steady Split/Normal Copy and Quick Split/Quick Resync.
- Protect access to local TI snapshots if the production volumes fail.
- Isolate production volumes from performance impacts caused by heavy I/O on local TI snapshots.
- Allow multiple scheduled mount operations (beyond the limits imposed by SI mirror counts) without affecting the original backup, through the use of Refreshed TI.
Continuous SI can be combined with all hardware operations (i.e. TI, RTI, SI, TC, UR or GAD), with the exception that a continuous SI S-VOL cannot also be the P-VOL of a remote replication (i.e. TC, Universal Replicator or GAD).
i.e. It is not possible to chain a remote replication from a continuous SI target.
- Repurpose on Demand - using continuous SI, keeps a close copy of the primary volume and allows pause and mount for repurposing.
- Protected Backup - using continuous SI to TI snapshots, retains snapshots in the event that the primary volume fails.
- DRU Protected Backup - using continuous SI to TI snapshots with DRU, retains snapshots with DRU lock in the event that the primary volume fails.
- Repurposing (TI) - using continuous SI to RTI snapshots, provides multiple repurposing copies, possibly in excess of the SI limit.
- Repurposing (SI) - using continuous SI to batch SI, provides a repurposing copy.
- Repurposing (SI) with Backup - using continuous SI to batch SI to TI snapshots, provides a repurposing copy with snapshots for protection.
- Repurposing (SI) with DRU Backup - using continuous SI to batch SI to TI snapshots with DRU, provides a repurposing copy with snapshots for protection with DRU lock.