TimeFinder SnapVX is interoperable with other HYPERMAX OS features under the following conditions.

SRDF

• Snapshots can be taken from R1 and R2 volumes in all SRDF modes (SRDF/S, SRDF/A, and SRDF/Metro).
• Write-pacing is not required when taking snapshots from SRDF/A R2 volumes.
• Snapshots cannot be taken of Storage Groups that contain a mix of SRDF and non-SRDF devices.
• Linked targets can be SRDF source volumes (SRDF R1) with the following considerations:

• Beginning with the PowerMaxOS Q3 2020 release, an SRDF R1 can be linked in nocopy mode.
• Prior code releases require an SRDF R1 to be linked in full copy mode.
• Using the -remote option with link and relink commands allow the R1 to stay ready on the SRDF link and automatically propagates the target data to the remote array.
• Linking an R1 to a snapshot initiates a full SRDF copy to the remote array.
• Relinking an R1 propagates the differential changes to the remote array. This applies to both copy and nocopy modes.

Service levels on PowerMaxOS 5978

• Service Level settings on source or target devices will have no effect on TimeFinder operations.
• Likewise, TimeFinder operations will have no effect on the Service Level of source or target devices.

FAST on HYPERMAX OS 5977

• Allocations owned by a source volume will be managed by the Service Level Objective of the source volumes SG.
• Allocations owned by a target volume will be managed by the Service Level Objective of the target volumes SG.
• Snapshot deltas will be managed by the Optimized Service Level Objective.
• Read-miss I/O to target tracks that are owned by the source volume will increment the FAST metrics for the source volume, not the target volume, and may contribute to the extent being promoted.
• Source and target volumes can be moved across SRPs while TimeFinder sessions are active.

Zero space reclaim

Zero space reclaim is supported on SnapVX source and target volumes.

Persistent allocations

Persistent Allocations are tracks that are unaffected by a standard reclaim operation. The user can mark and unmark tracks as persistent with the Solutions Enabler symdev or symsg commands, and with Unisphere.

• The considerations for Persistent Allocations with SnapVX are as follows:
• Snapshots can be taken of a volume that has Persistent Allocations. However, restores from a snapshot are blocked if the source volume has any Persistent Allocations. The user needs to remove the Persistent Allocations from the entire volume to allow the restore operation. Persistent Allocations can be reset on the source volume once the restore session is terminated.
• Volumes with persistent allocations cannot be used as linked targets. Likewise, persistent allocations cannot be set on linked targets.

Non-Disruptive Migration

Non-Disruptive Migration (NDM) was introduced in the HYPERMAX OS Q3 2016 Service Release. For more in-depth information, see the VMAX Non-Disruptive Migration Configuration and Best Practices Technical Notes, available on dellemc.com.

• Existing TimeFinder sessions from an NDM device can remain in place during the migration.
• New replication from an NDM device can be configured during a specific point in the migration process.
• An NDM device, source or target, cannot be the target of a TimeFinder session.
• The TimeFinder session cannot restore data back to the NDM device at any time during the migration session.

Data reduction on PowerMax arrays

The Data Reduction feature in PowerMaxOS 5978 on PowerMax arrays consists of deduplication and compression. For more information about Data Reduction, see the Data Reduction with Dell EMC PowerMax white paper available on dellemc.com.

Nocopy Sessions (SnapVX, VP Snap):

• Compressed source data remains compressed when becoming snapshot data.
• Uncompressed source data may become compressed as it becomes snapshot data.
• Uncompressed snapshot data may be compressed as it becomes less active.
• Snapshot data is available for deduplication.
• Read activity through a nocopy linked target to uncompressed snapshot data may prevent the data from being compressed.
• Read activity through a nocopy linked target to compressed snapshot data may cause the snapshot data to be decompressed.
• Enabling data reduction on a nocopy linked target will only effect on data owned by the linked target.

Copy Sessions (SnapVX Full Copy Linked Targets, Clone, Mirror):

• The data reduction settings for both the source and the target affect copy sessions.
• When enabled on the SG for both the source and full copy targets, data is not duplicated to the target volume during the copy operation. This has the additional benefit of allowing a SnapVX full copy linked target to also be an SRDF R1 without consuming additional backend capacity.
• When data reduction is enabled on the source only, the data is decompressed before being allocated to the target.
• When data reduction is enabled on the target only, the data is compressed before being allocated to the target. Target data may be deduplicated given data on other volumes in the system, but not with the source volume.
• It is not recommended to change the data reduction settings in between differential operations (that is, disabling before each differential operation and then enabling again after the copy completes) as this causes data to go through needless compression, decompression, or deduplication cycles.

Note: The set mode (SnapVX and Clone) and precopy (Clone) operations do not have the full deduplication efficiencies. Changing mode from nocopy to full copy, or creating a clone with precopy, may use more backend capacity than using copy mode alone.

Inline compression on VMAX All Flash arrays

Inline Compression was introduced in the HYPERMAX OS 5977.952.892 Q3 2016 Service Release. For more in-depth information about compression, see the Data Reduction with Dell EMC PowerMax white paper available on dellemc.com.

Nocopy Sessions (SnapVX, VP Snap):

• Compressed source data remains compressed when becoming snapshot data.
• Uncompressed source data may become compressed as it becomes snapshot data.
• Uncompressed snapshot data may be compressed as it becomes less active.
• Read activity through a nocopy linked target to uncompressed snapshot data may prevent the data from being compressed.
• Read activity through a nocopy linked target to compressed snapshot data may cause the snapshot data to be decompressed.
• The compression setting of a nocopy linked target will only effect on data owned by the linked target.

Copy Sessions (SnapVX Full Copy Linked Targets, Clone, Mirror):

• The compression settings for both the source and the target affect copy sessions.
• When compression is enabled on both the source and the target, the data is decompressed before the copy and then compressed again to allocate for target.
• When compression is enabled on the source only, the data is decompressed before being allocated to the target.
• When compression is enabled on the target only, the data is compressed before being allocated to the target.
• Copy times may vary due to decompression and compression of the data.
• It is not recommended to change the compression settings in between differential operations (that is, disabling compression before each differential operation and then enabling again after the copy completes) as this causes data to go through needless compression or decompression cycles.