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PowerMax local replication includes TimeFinder/SnapVX (snapshots) and TimeFinder/Clone (clones), and PowerMax remote replication includes the SRDF product line. TimeFinder provides point-in-time local replication and data protection, and SRDF provides continuous local replication and data protection.
PowerMax local and remote replication are integrated so that remote snapshots or clones can be easily taken from or restored to SRDF target devices. One benefit of this integration is that it allows the creation of remote copies of the source application without interrupting remote replication. If the source application data is corrupted, the remote snapshot (or clone) and SRDF can restore the data in parallel to the source volumes. Both PowerMax local and remote replication send only changed data when applicable, except when an initial full sync of SRDF is required.
TimeFinder software on PowerMax 2500 and PowerMax 8500 storage systems protects applications through two complementary products: TimeFinder/SnapVX (snapshots) and TimeFinder/Clone (clones). Choosing between snapshots or clones depends on the use case. Both snapshots and clones can be created using the Solutions Enabler command-line interface (CLI), REST APIs, or with Unisphere.
Snapshots are always associated with their source volumes and cannot be directly accessed. Instead, they can either be restored to their source volumes or linked to a set of matching target volumes, which are then referred to as linked target volumes, as shown in the following figure. The linked target volumes can be made visible to a host so that the snapshot data can be accessed. In addition, it is not possible to restore the linked target volumes directly. Instead, a new snapshot is created from the linked target volumes and linked back to the original source volumes.
Snapshots also have user-friendly names and versions (also called generations), can be automated with snapshot policies, can have automatic expiration, can be made secure (so they cannot be deleted before their expiration), and are natively consistent.
There are two ways of creating snapshots: manually (including scheduled snapshots) and automatically (using snapshot policies). A source volume can have up to 256 manual snapshots or up to 1,024 automated snapshots. Regardless of how a snapshot was created, it can be linked to up to 1,024 target volumes, allowing high scalability and flexibility of local replications.
PowerMax clones can be directly presented to hosts, restored directly to their clone source volumes, or used as a new source for local replications, as shown in the following figure:
Clone operations are considered manual as clones do not have policies in Unisphere. Up to 256 clones can be created for each source volume.
Both snapshots and clones share storage allocations for high efficiency and performance, where only data differences consume additional storage capacity. Restoring data swaps data pointers rather than copying data. Metadata associated with snapshots and clones scales proportionally to the number of changes. These capabilities lead to better ease-of-use, efficiency, scalability, and performance.
Starting with PowerMaxOS 10, a new internal mechanism replaces the legacy define scan of snapshot metadata. As a result, there is no need to wait before performing snapshot cascaded operations such as creating a new snapshot from snapshot-linked target devices, or before unlinking a snapshot.
The copy and nocopy options, which area snapshot legacy features, are no longer used. All snapshots are space efficient (nocopy) and consume additional storage capacity only based on data changes after snapshot creation.
Notes:
Clone creation requires the use of the -consistent flag to create consistent clones. This behavior may change in the future.
Snapshot and clone interoperability is not allowed on cascading sessions. For example, a snapshot cannot be taken from a clone target, and clones cannot be created from a volume that has a snapshot in restore state.
The following table shows the snapshots and clones feature summary:
Feature | SnapVX Snapshots | SnapVX Linked Targets | Clones |
Scalability (per SG) | 1024 | 1024 | 256 |
Integrated scheduling | P |
|
|
Nonmodifiable (protected) | P |
|
|
Secure | P |
|
|
R/W access |
| P | P |
Device expansion | P | P |
|
Direct restore to source | P |
| P |
Write-consistent | P | P | Requires the -consistent flag |
Ship data using SRDF |
| P | P |
Reset to original point-in-time copy |
| P |
|
For more information about PowerMax snapshots and clones, see the Dell PowerMax 2500 and 8500: TimeFinder SnapVX Snapshots and Clones white paper.
SRDF is PowerMax remote replication software that offers extensive flexibility, scale, and features, while maintaining high performance and low latencies.
An SRDF group is a collection of SRDF ports from two PowerMax systems connected by an FC- or IP-based network. When source and target volumes are added to the SRDF group (for example, using SGs for ease of management), a replication session can be started to obtain a copy of the data between the PowerMax systems. PowerMax systems support up to 2,048 SRDF groups (up to 250 groups if one of the systems is an older generation PowerMax system).
SRDF supports many topologies:
The following key SRDF modes include:
For more information about SRDF/Metro, see the Dell PowerMax and VMAX All Flash: SRDF/Metro Overview and Best Practices white paper.