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Performance Implications of Storage I/O Control in vSphere Environments with Shared Storage

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

Sioc-adv
 

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

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