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Host I/O Limits is a feature of the PowerMax which allows users to place limits on the front-end bandwidth and IOPS consumed by applications on the array.
Limits are set on a per-storage-group basis. As users build masking views with these storage groups, limits for both maximum front-end IOPS and MB/s are evenly distributed across the directors within the associated masking view. The array monitors bandwidth and IOPS to ensure that they do not exceed the user-specified maximum.
The benefits of implementing Host I/O Limits are:
Configure the Host I/O Limits on a group of devices by adding a Host I/O Limit to a storage group. A masking view is then created using that storage group. This view applies the Host I/O Limit that is defined on the storage group to the devices in the storage group for the ports in the port group, and any child storage groups. The Host I/O Limit for a storage group can be either active or inactive.
Note: Usually, the total Host I/O Limit may only be achieved with proper host load balancing between directors by multipath software on the hosts such as PP/VE.
The Host I/O Limit can be set using the SYMCLI command symsg or Unisphere. Figure 115 demonstrates the use of SYMCLI to set the Host I/O Limit.
Using Unisphere go to Storage Groups and select one of them to bring up the properties of the storage group. Select Set Host I/O Limits, enter the pertinent limit, by MB/sec or I/O/sec or both, and press OK as seen in Figure 116.
Host I/O Limits can also be set during provisioning. In the following example in Unisphere for PowerMax in Figure 117, two child storage groups are assigned different values. One storage group is limited by MB/s, and the other by I/O/s. Host I/O Limits can be changed at will or removed at any time.
For more information about Host I/O Limits, see the Technical Note available on the Dell support site.