Now you can switch the role of the copies online (step 3), and test the performance of the new  pool. If you are done testing your lower performance pool, you can split or delete the old copy  in tier 1, or switch back to tier 1 in seconds, in case tier 2 pool did not meet your performance  requirements.  You can set a limit on the number of I/O operations that are accepted for a volume. The limit is  set in terms of I/O operations per second (IOPS) or MBps. By default, no I/O throttling rate is  set when a volume is created.I/O throttling is also referred to as I/O governing.  Base the choice between I/O and MB as the I/O governing throttle on the disk access profile  of the application. Database applications generally issue large amounts of I/O, but they  transfer only a relatively small amount of data. In this case, setting an I/O governing throttle  that is based on MBps does not achieve much. It is better to use an IOPS as a second  throttle.  At the other extreme, a streaming video application generally issues a small amount of I/O,  but it transfers large amounts of data. In contrast to the database example, setting an I/O  governing throttle that is based on IOPS does not achieve much, so it is better to use an  MBps throttle. An I/O governing rate of  0  does not mean that zero IOPS (or MBps) can be achieved. It  means that no throttle is set. 6.10 I/O throttling 6.10.1 Defining throttle on a volume Note:  Consider the following points: To define a throttle on a volume, complete the following steps: 1. From the Volumes window, select the wanted volume to throttle, as shown in Figure 6-54. GLYPH<SM590000> I/O governing on a Metro Mirror and Global Mirror secondary volume does not affect the  rate of data copy from the primary volume. GLYPH<SM590000> I/O governing does not affect FlashCopy and data migration I/O rates. Figure 6-54 Edit Throttle Chapter 6. Volume configuration  353