Chapter 11. Advanced Copy Services 531
The quota of background copy (configured on the intercluster link) is divided evenly between 
all nodes that are performing background copy for one of the eligible relationships. This 
allocation is made irrespective of the number of disks for which the node is responsible. Each 
node in turn divides its allocation evenly between the multiple relationships that are 
performing a background copy.
The default value of the background copy is 25MBps per volume.
11.6.16  Thin-provisioned background copy
MM/GM relationships preserve the space-efficiency of the master. Conceptually, the 
background copy process detects a deallocated region of the master and sends a special 
zero buffer to the auxiliary.
If the auxiliary volume is thin-provisioned and the region is deallocated, the special buffer 
prevents a write and, therefore, an allocation. If the auxiliary volume is not thin-provisioned or 
the region in question is an allocated region of a thin-provisioned volume, a buffer of “real” 
zeros is synthesized on the auxiliary and written as normal.
11.6.17  Methods of synchronization
This section describes two methods that can be used to establish a synchronized 
relationship.
Full synchronization after creation
The full synchronization after creation method is the default method. It is the simplest method 
in that it requires no administrative activity apart from issuing the necessary commands. 
However, in certain environments, the available bandwidth can make this method unsuitable. 
Use the following command sequence for a single relationship:
/SM590000Run mkrcrelationship without specifying the -sync option.
/SM590000Run startrcrelationship without specifying the -clean option.
Synchronized before creation
In this method, the administrator must ensure that the master and auxiliary volumes contain 
identical data before creating the relationship by using the following technique:
/SM590000Both disks are created with the security delete feature to make all data zero.
/SM590000A complete tape image (or other method of moving data) is copied from one disk to the 
other disk.
With this technique, do not allow I/O on the master or auxiliary before the relationship is 
established. Then, the administrator must run the following commands:
/SM590000Run mkrcrelationship with the -sync flag.
/SM590000Run startrcrelationship without the -clean flag.
Important: The background copy value is a system-wide parameter that can be changed 
dynamically, but only on a per-system basis and not on a per-relationship basis. Therefore, 
the copy rate of all relationships changes when this value is increased or decreased. In 
systems with many remote copy relationships, increasing this value might affect overall 
system or intercluster link performance. The background copy rate can be changed to 
1 - 1000 MBps.