Chapter 7. Volumes 273
7.5  I/O throttling
You can set a limit on the number of I/O operations that are realized by a volume. This 
limitation is called I/O throttling or governing. 
The limit can be set in terms of number of I/O operations per second (IOPS) or bandwidth 
(MBps, GBps, or TBps). By default, I/O throttling is disabled, but each volume can have up to 
two throttles defined: one for bandwidth and one for IOPS.
When deciding between the use of IOPS or bandwidth as the I/O governing throttle, consider 
the disk access profile of the application that is the primary volume user. Database 
applications generally issue large amounts of I/O operations, but transfer a relatively small 
amount of data. In this case, setting an I/O governing throttle that is based on bandwidth 
might not achieve much. A throttle based on IOPS would be better suited to this use case.
Conversely, a video streaming application generally issues a small amount of I/O, but 
transfers large amounts of data. Therefore, it is better to use a bandwidth throttle for the 
volume in this case.
An I/O governing rate of 0 does not mean that zero IOPS or bandwidth can be achieved for 
this volume; rather, it means that no throttle is set for this volume.
Note: Consider the following points:
/SM590000I/O governing does not affect FlashCopy and data migration I/O rates.
/SM590000I/O governing on Metro Mirror or Global Mirror secondary volumes does not affect the 
rate of data copy from the primary volume.