White Papers

10 Dell PS Series Arrays: Advanced Storage Features in VMware vSphere | TR1066
4 Storage I/O Control
Storage I/O Control (SIOC) ensures that the excessive storage I/O demands of a particular VMDK do not
negatively impact the storage I/O needs of other VMDKs residing on the same datastore. Previously, this
has been resolved though administrative tasks such as careful VM placement, reactive monitoring of
VMDK I/O, and over-sizing of the environment to handle occasional I/O spikes.
With SIOC, the reactive monitoring task is conducted by vSphere across all ESX/ESXi hosts and the reactive
action is performed automatically and instantaneously by vSphere, enabling administrators to more
efficiently utilize their storage environments.
The advantages of using SIOC include:
Performance protection: SIOC ensures that all VMDKs receive a fair share or assigned share of I/O needs
regardless of the I/O they demand during period of congestion.
Better utilization of storage assets: The storage environment no longer needs to be oversized to cover
occasional I/O peaks. Rather, these peaks are leveled out by SIOC.
Offering two deployment options, SIOC can provide equal treatment to all VMDKs sharing the datastore,
or it can favor or disfavor certain VMDKs through the use of disk shares. Regardless of the granularity of
implementation, SIOC operates in the same way, but the impact to VMDKs with excessive I/O
consumption may differ.
SIOC works by monitoring the I/O latency of a datastore. When that latency exceeds the threshold that
has been set (30ms by default), SIOC will engage and enforce the assigned disk shares. SIOC achieves this
by restricting the number of queue slots available to the VMDKs that are consuming more than their
assigned share, and provides the previously deprived VMDKs with improved storage performance.
While SIOC does not eliminate the need for SAN monitoring, it means that the SAN does not need to be
actively monitored, freeing up the storage administrator to deal with more important tasks. If SIOC is
engaging for significant periods of time, the administrator may need to add additional I/O capacity or
relocate I/O-intensive VMDKs.