Red Hat NETSCAPE MANAGEMENT SYSTEM 4.5 User Manual download pdf (Page 210)

Disks

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Sharing the SCSI Bus

Normally, VMware ESX Server enforces locking and does not allow two virtual

machines to access the same virtual disk (VMFS file) at the same time. If a second

virtual machine tries to access a VMFS file, it gets an error and does not power on.

However, it is often useful to have more than one virtual machine share a disk in order

to provide high availability. This configuration is commonly used for disk-based

failover, in which one machine takes over running an application when the primary

machine fails. The data required for the application is typically stored on a shared disk,

so the backup machine can immediately access the necessary data when the failover

occurs.

The bus sharing setting is used to determine if virtual machines are allowed to access

the same virtual disk simultaneously.

Setting Bus Sharing Options

Use the VMware Management Interface to change the bus sharing settings for each

virtual machine that will access the same virtual disk simultaneously. Log in to the

management interface as the appropriate user and be sure the virtual machine you

want to configure is powered off. Point to the terminal icon for the virtual machine

you want to configure and click Edit Configuration. In the SCSI Devices section,

choose the bus sharing setting you want, then click Save Changes. There are three

options.

• None: Disks cannot be shared by other virtual machines

• Virtual: Disks can be shared by virtual machines on same server

• Physical: Disks can be shared by virtual machines on any server

To enable sharing of virtual disks, choose Virtual or Physical. All virtual disks on the

specified virtual bus will be sharable and have the specified mode.

If the bus sharing is virtual, only virtual machines on the same physical machine will

be able to share disks. This setting allows for a “cluster-in-a-box” configuration, in

which all members of a high-availability cluster are on the same physical machine.

This setup is useful for providing high availability when the likely failures are due to

software or administrative errors.

If the bus sharing is physical, virtual machines on different physical machines will be

able to share disks. In this case, the VMFS holding the virtual disks must be on a

physically shared disk, so all of the physical machines can access it. This setup is useful

for providing high availability when the likely failures also include hardware errors.

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Red Hat NETSCAPE MANAGEMENT SYSTEM 4.5 User Manual Page 210