VMware VROOM! Blog

vSphere based virtualized datacenters often employ a shared storage infrastructure to support clusters of vSphere hosts. Applications running in virtual machines (VM) on vSphere hosts share the storage resources for their I/O needs. Performance of applications can be impacted when VMs contend for storage resources that are shared. Without proper access control for sharing the resources, the performance of all applications tend to get affected in a non-trivial way. Storage I/O Control (SIOC), a new feature offered in VMware vSphere 4.1, provides a dynamic control mechanism for proportional allocation of shared storage resources to VMs running on multiple hosts. The experiments conducted in VMware performance labs show that:

• SIOC prioritizes VMs’ access to shared I/O resources based on disk shares assigned to them. 

•  If the VMs do not fully utilize their portion of the allocated I/O resources on a shared datastore, SIOC redistributes the unutilized resources to those VMs that need them in proportion to the VMs’ disk shares.

• SIOC minimizes the fluctuations in performance of a critical workload during periods of I/O congestion. For the test case executed at VMware labs, limiting the fluctuations to a small range resulted in as much as a 26% performance benefit compared to that with the default configuration (figure 1).

Figure 1. Application throughput with and without SIOC enabled

For further details, read the white paper titled “Managing Performance Variance of Applications Using Storage I/O Control” at http://www.vmware.com/resources/techresources/10120