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Chapter 1. Introduction 5
When a FlashCopy operation is invoked, it takes only a few seconds to complete the process
of establishing the FlashCopy pair and creating the necessary control bitmaps. Thereafter,
you have access to a Point-in-Time Copy of the source volume. As soon as the pair has been
established, you can read and write to both the source and target volumes.
After creating the bitmap, a background process begins to copy the real data from the source
to the target volumes. If you access the source or the target volumes during the background
copy, FlashCopy manages these I/O requests, and facilitates both reading from and writing to
both the source and target copies. When all the data has been copied to the target, the
FlashCopy relationship is ended.
1.1.2 Remote Mirror and Copy RMC (formerly Peer-to-Peer Remote Copy)
The Remote Mirror and Copy (RMC) license authorization enables several Copy Services
functions depending on the configuration and settings you use. RMC is a flexible data
mirroring technology that allows replication between volumes on two or more disk storage
systems. You can also use this feature for data backup and Disaster Recovery.
Remote Mirror and Copy is an optional function. To use it, you must purchase the Remote
Mirror and Copy function authorization code #5300 RMC for the required DS6800 storage
server machine type 1750.
DS6000 Storage Units can participate in Remote Mirror and Copy solutions with another
DS6000, or with the ESS Model 750, ESS Model 800, and DS8000 Storage Units. To
establish an RMC (formerly PPRC) relationship between the DS6000 and the ESS, the ESS
needs to have licensed internal code (LIC) Version 2.4.3.65 or later.
The Remote Mirror and Copy feature can operate in the following modes:
Metro Mirror (formerly Synchronous PPRC)
Metro Mirror provides real-time mirroring of logical volumes between two DS6000s that you
can place up to 300 km from each other. It is a synchronous copy solution where write
operations are completed on both copies (local and remote site) before they are considered
to be complete.
Global Copy (formerly PPRC-XD)
Global Copy copies data non-synchronously and over longer distances than is possible with
Metro Mirror. When operating in Global Copy mode, the source volume sends a periodic,
incremental copy of updated tracks to the target volume, instead of sending a constant
stream of updates. This causes less impact to application writes for source volumes and less
demand for bandwidth resources, while allowing a more flexible use of available bandwidth.
Global Copy does not keep the sequence of write operations. Therefore, the copy is normally
fuzzy, but you can make a consistent copy through synchronization (called a go-to-sync
operation). After the synchronization, you can issue FlashCopy at the secondary site to make
the backup copy with data consistency. After the establishment of the FlashCopy, you can
change the mode back to non-synchronous mode.
If you want to make a consistent copy with FlashCopy, you must purchase a Point-in-Time
Copy function authorization license for the secondary Storage Unit.
Note: When you change from synchronous to non-synchronous mode, you must suspend
first, and then change mode to non-synchronous mode.