By Lisa Gecko
Storage is the slowest and most complex host resource, and is capable of severely handicapping your virtual machines (VMs) performance during business critical processing. In a VMware environment, Storage I/O Control (SIOC) provides much needed control of storage I/O and is used to ensure that the performance of your business-critical VMs are not affected by VMs from other hosts when there are competing demands for I/O resources. vSphere 5’s new Storage I/O Control now supports NFS and network-attached storage (NAS)–based shares on shared datastores. This allows cloud hosting companies to set storage quality of service priorities per virtual machine for better access to storage resources for high-priority applications. It also enables enforcement of storage service level agreements (SLAs) with NSF. Let’s take a closer look.
Storage I/O Control allows cloud hosting administrators to control the amount of access virtual machines have to the I/O queues on a shared datastore. This ensures that virtual machines running business-critical applications have higher priority to access the I/O queue than that of other virtual machines sharing the same datastore. And the new Storage APIs and resulting Storage Awareness in vSphere 5 eliminates the need for maintaining massive spreadsheets detailing the storage capabilities of each LUN that are needed to guarantee the correct SLA to virtual machines. While vSphere 4.1 supported SIOC on VMFS-based datastores that used SAN with iSCSI and Fibre Channel, vSphere 5s SIOC support has been extended to NFS-based datastores.
Storage I/O Control now dynamically regulates multiple virtual machines’ access to shared I/O resources, based on disk shares assigned to the virtual machines. It also helps isolate performance of latency-sensitive applications that employ smaller (<8KB) random I/O requests. This feature has been shown to increase performance by as much as 20%. Simultaneously, it now redistributes unutilized resources to those virtual machines that need them in proportion to the virtual machines’ disk shares, resulting in a fair allocation of storage resources without any loss in utilization. And in order to provide reliable performance during critical workloads, it limits performance fluctuations to a small range during periods of I/O congestion. This boosts performance by 11% compared to an unmanaged scenario without Storage I/O Control.
Storage I/O Control provides a dynamic control mechanism for managing virtual machines’ access to I/O resources, Fibre Channel (FC), iSCSI or NFS, in a cluster. It delivers the same performance benefits to NFS datastores as it does to already supported FC or iSCSI datastores. Tests have shown that with the right balance of workloads, Storage I/O Control might improve performance of critical applications by as much as 10%, with a latency improvement per I/O operation of as much as 33%.
Recent tests conducted at VMware Performance Engineering lab studied several performance aspects of SIOC and found that the enhanced 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 resulted in a significant performance boost as well. Tests found that SIOC helped databases with I/Os ?8K workload achieved higher performance when sharing the underlying datastore with a workload that used large-sized I/O requests. 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 confirmed this results in a more reliable and consistent use of cloud hosting resources.