Red Hat NETSCAPE MANAGEMENT SYSTEM 4.5 User Manual download pdf (Page 257)

Resource Management

257

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Disk Bandwidth Management

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

disk. 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 console operating

system’s procfs interface or the Perl API.

Reasonable defaults are used automatically when you do not specify parameters

explicitly. Information about current disk bandwidth allocations and other status is

available via the management interface, the console operating system’s procfs

interface and the Perl API.

Allocation Policy

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. 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.

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Red Hat NETSCAPE MANAGEMENT SYSTEM 4.5 User Manual Page 257