IBM Storwize V7000, Introduction And Implementation Manual, Page: 384 / 670

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IBM Flex System V7000 Storage Node Introduction and Implementation Guide
9.1 Services provided
IBM Flex System V7000 Storage Node features the following copy services capabilities:
򐂰 Flashcopy
򐂰 Synchronous remote copy
򐂰 Asynchronous remote copy
These functions are useful for making data copies for backup, application test, disaster
recovery, and so on.
To decide on the functions to be used to meet a need, it is best to plan for the results wanted.
Here are two points to be considered for this planning:
򐂰
Recovery point objective (RPO): The point at which the data needs to be able to be
recovered to after a disaster occurs.
򐂰 Recovery time objective (RTO): The amount of time that the recovery can take to get back
up and running after a disaster occurs.
How these objectives are defined can dictate what service capabilities might need to be
implemented. In some cases, it might be decided that the use of a combination of the
services might better meet the over all need rather than trying to use one specific service. It
can be true for cases where a solution might prove to be cost prohibitive for an environment.
9.2 FlashCopy
The FlashCopy function of IBM Flex System V7000 Storage Node lets you create a
point-in-time copy
of one or more volumes. In this section, we describe the structure of
FlashCopy and provide details about its configuration and use.
You can use FlashCopy to solve critical and challenging business needs that require
duplication of data on your source volume. Volumes can remain online and active while you
create consistent copies of the data sets. Because the copy is performed at the block level, it
operates below the host operating system and cache and is therefore not apparent to the
host.
While the FlashCopy operation is performed, the source volume is frozen briefly to initialize
the FlashCopy bitmap and then I/O is allowed to resume. Although several FlashCopy options
require the data to be copied from the source to the target in the background, which can take
time to complete, the resulting data on the target volume copy appears to have completed
immediately. This task is accomplished through the use of a bitmap (or bit array) that tracks
changes to the data after the FlashCopy is initiated, and an indirection layer, which allows
data to be read from the source volume transparently.
9.2.1 Business requirements for FlashCopy
When deciding if FlashCopy addresses your needs, you need to adopt a combined business
and technical view of the problems you need to solve. Determine what your needs are from a
business perspective, and then determine if FlashCopy fulfills the technical needs of those
business requirements.
Flushing: Because FlashCopy operates at the block level, below the host operating
system and cache, those levels do need to be flushed to create a consistent FlashCopy
copy image for a point in time.