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Because SIOC and Dell Host I/O Limits can restrict the amount of I/O either by IOPS per second or MB per second, you may question their interoperability. The two technologies can be used together, though the limitations around SIOC reduce its benefits as compared to Host I/O Limits. There are a few reasons for this issue.
First, SIOC can only work against a single datastore that consists of a single extent. In other words, one LUN. Therefore, only the VMs on that datastore are subject to any Storage I/O Control and only when the response threshold is breached. In other words, it is not possible to setup any VM hierarchy of importance if the VMs do not reside on the same datastore. In contrast, Host I/O Limits work against the storage group as a whole which typically consists of multiple devices. In addition, child storage groups can be used so that individual LUNs can be singled out for a portion of the total limit. A VM hierarchy can be established across datastores because each device can have a different Host I/O limit but be in the same storage group. Thus they are bound by the shared parental limit.
The other problems to consider with SIOC is the type and number of disks. SIOC is set at the VMDK level. If there is more than one VMDK per VM, each VMDK requires a separate I/O limit. Testing has shown that this configuration makes it difficult to achieve an aggregate IOPS number. That is, unless the access patterns of the application are known so well that the number of I/Os to each VMDK can be determined. For example, if you want to allow 1000 IOPs for a VM with two VMDKs, it may seem logical to limit each VMDK to 500 IOPs. However, if the application generates two I/Os on VMDK for every I/O on the other VMDK, the most IOPs that can be achieved is 750. The reason is that one VMDK reaches the 500 IOPS limit. If Raw Device Mappings are used in addition to VMDKs, the exercise becomes impossible as they are not supported with SIOC.
SIOC can, however, be useful in the environment. If the VMs that require throttling always share the same datastore, then using SIOC is the only way to limit I/O among them in the event there was contention. In such an environment, a Host I/O Limit could be set for the device backing the datastore. That way, the VMs that are not throttled could generate IOPs up to another limit if wanted.
Note: The PowerMax limits the I/O when using Host I/O Limits. Unless SIOC is set at the datastore level, individual VMs on a particular device are free to generate their potential up to the Host I/O limit, regardless of latency.