This article is designed to provide an overview of storage copy services and describe what functions do copy services provide, how do they work, what financial and business benefits do copy services bring and how to best implement copy services.
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What are copy services?
Storage copy services are functions that provide the foundation for data duplication, migration and disaster recovery. In general, there are two classes of copy services, including:
- Local copy services - which provide "point-in-time" duplication and replication of data
- Remote copy services - which provide a basis for disaster recovery and data migration typically over a distance
How do copy services work?
Copies can be made asynchronously or synchronously. Most copies are asynchronous due to expense, distance limitations and the overheads associated with synchronous copy. Typically, within each class of copy, either full images ('clones') are copied or only recent changes are copied to the volume. In either case, the master volume has read:write capability while the shadow volume is a point-in-time copy (unless synchronous operations are in effect).
Copy services allocate a master volume and a single or often multiple shadow volumes that are typically point-in-time copies. Shadow copies are used for backup, temporary storage, data movement and migration among other applications. With asynchronous operations, when a write is initiated to the master copy, changed data are migrated to the shadow copy as system resources allow. Changes are logged and indexed so that a point-in-time copy can be accessed as required.
What benefits do copy services bring?
Copy services enable very high speed replication with little disruption to application performance and availability. There are a variety of uses for copy services such as local mirroring, which increases availability and flexibility, data migration which allows for non-disruptive movement of data and disaster recovery, which protects key corporate assets from destruction.
How to implement copy services
Implementing copy services involves several steps including:
- Analyzing the need for copy services
- Designing appropriate copy services for an organization
- Building a copy services infrastructure
- Implementing copy services
- Operating copy services on a day-by-day basis