Storage I/O Control (SIOC) allows administrators to control the amount of access virtual machines have to the I/O queues on a shared datastore. With this feature, administrators can ensure that a virtual machine running a business-critical application has a higher priority to access the I/O queue than that of other virtual machines sharing the same datastore. In vSphere 4.1, SIOC was supported on VMFS-based datastores that used SAN with iSCSI and Fibre Channel. In vSphere 5, SIOC support has been extended to NFS-based datastores.
Recent tests conducted at VMware Performance Engineering lab studied the following aspects of SIOC:
- The performance impact of SIOC: A fine-grained access management of the I/O queues resulted in a 10% improvement in the response time of the workload used for the tests.
- SIOC’s ability to isolate the performance of applications with a smaller request size: Some applications like Web and media servers use I/O patterns with a large request size (for example, 32K). But some other applications like OLTP databases request smaller I/Os ≤8K. Test findings show that SIOC helped an OLTP database workload to achieve higher performance when sharing the underlying datastore with a workload that used large-sized I/O requests.
- The intelligent prioritization of I/O resources: SIOC monitors virtual machines’ usage of the I/O queue at the host and dynamically redistributes any unutilized queue slots to those virtual machines that need them. Tests show that this process happens consistently and reliably.
For the full paper, see Performance Implications of Storage I/O Control–Enabled NFS Datastores in VMware vSphere 5