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VMware ESX Server 2.1
Features | Documentation | Knowledge Base | Discussion Forums ESX Server provides dynamic control over the relative amount of disk bandwidth allocated to each virtual machine. You can control disk bandwidth separately for each physical disk or logical volume. The system manages the allocation of disk bandwidth to virtual machines automatically based on allocation parameters and system load. This is done in a way that maintains fairness and tries to maximize throughput. You may specify initial disk bandwidth allocation values for a virtual machine in its configuration file. You may also modify disk bandwidth allocation parameters dynamically using the VMware Management Interface, the procfs interface on the service console or the VMware Scripting API. Reasonable defaults are used automatically when you do not specify parameters explicitly. However, if you plan to run a virtual machine that will have disk-intensive workloads, such as a database, or file server, then you may want to increase its disk shares. Information about current disk bandwidth allocations and other status is available via the management interface, the procfs interface on the service console and the VMware Scripting API. ESX Server uses a modified proportional-share allocation policy for controlling disk bandwidth per virtual machine. This policy attempts to control the disk bandwidth used by a virtual machine to access a disk while also trying to maximize throughput to the disk. Disk bandwidth shares entitle a virtual machine to a fraction of the bandwidth to a disk or LUN. For example, a virtual machine that has twice as many shares as another for a particular disk is entitled to consume twice as much bandwidth to the disk, provided that they are both actively issuing commands to the disk. Bandwidth consumed by a virtual machine is represented in consumption units. Every SCSI command issued to the disk effectively consumes one unit by default and additional units proportional to the size of the data transfer associated with the command. Throughput to the disk is maximized through the use of a scheduling quantum for disk requests from a virtual machine to a disk. A virtual machine is allowed to issue a number of requests to a disk (the scheduling quantum) without being preempted by another virtual machine. The issuing of a multiple requests without preemption is applicable only if these requests access sequential sectors on the disk. |
