HP XP7 Storage - Manual (Page 8)

Establishing a Compatible FlashCopy relationship
Compatible FlashCopy provides a fast data replication capability that enables you to copy the
source data to a target volume virtually or physically. A copy pair created by Compatible FlashCopy
is called a relationship. Once a relationship has been created, hosts can access the data that is
copied to the target volume.
You can specify a range of data to be copied, which is called an extent, when you establish a
Compatible FlashCopy relationship. In addition, you can make multiple copies of data from one
copy source. When you specify only a part of a volume (that is, an extent) as the copy source, the
capacity of the source volume (S-VOL) and the target volume (T-VOL) can be different. However,
the specified target volume or extent must have a minimum size equal to that of the source volume
or extent. You can even specify both copy source and copy target within the same volume.
To establish a Compatible FlashCopy relationship, you need to specify the source volume and the
target volume. When you want to copy data according to dataset, you specify the copy range as
an extent in addition to the source and target. The smallest extent is a track. For Compatible
FlashCopy a dataset is basically an extent for which the addresses are determined by the dataset
entries in the VTOC.
Compatible FlashCopy allows you to establish up to 16 relationships from one extent, as shown
in the following figure. Also as shown below, you cannot create a cascaded relationship. That is,
an extent that is already set as a copy target cannot be used as a copy source to create a new
relationship.
In the HP XP7 Storage system, Compatible FlashCopy relationship information is stored in control
areas on the data drives and staged into memory to enable high-speed data access. However,
when the memory is cleared, such as during system installation or power-on after a scheduled
outage or power failure, establishment of relationships may take longer than after the storage
system has been operating for a while.
8 About Compatible FlashCopy