VMware GSX 3 - Manual (Page 203)

C H A P T E R 7 High-Availability Configurations with VMware GSX Server
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try to share a disk among virtual machines located on different hosts, data could
be corrupted or lost.
• Do not share a disk on SCSI bus 0. This bus is usually used for the boot disk. If you
share the boot disk, you run the risk of corrupting it, as the boot program is not
aware that the disk is being shared and can write to the disk regardless of
whether or not it is being shared. It is far more secure to use SCSI reservation on
a data disk located on a different bus.
• If only one running virtual machine is using a given disk, and it is running
applications that do not use SCSI reservation, then the disk’s performance might
be degraded slightly.
• At this time, if one virtual machine does not have SCSI reservation enabled for its
virtual disk, but another virtual machine does have SCSI reservation enabled for
the same virtual disk, GSX Server does allow the disk to be shared. However, any
virtual machine not configured for SCSI reservation that tries to access this disk
concurrently can cause corruption or data loss on the shared disk. VMware
recommends you take care when sharing disks.
• If you need to shrink or defragment the virtual disk (which can be done only with
a growable virtual disk), first disable SCSI reservation and make sure the virtual
disk is not being used by any other virtual machine.
To disable SCSI reservation for all SCSI disks in a virtual machine, open the
configuration file and comment out or remove the scsi<x>.sharedBus =
"virtual" line and make sure the disk.locking line is set to "true".
If you want to disable SCSI reservation for only a specific SCSI disk on a shared
bus, change the scsi<x>:<y>.shared = "true" line in the
configuration file to scsi<x>:<y>.shared = "false"; you can also
comment out the line.
• In a Windows virtual machine, some disk errors are recorded in the Windows
event log in normal operation. These error messages have a format similar to
"The driver detected a controller error on
\Device\Scsi\BusLogic3"
The errors should appear in the log periodically only on the passive node of the
cluster and should also appear when the passive node is taking over during a
failover. The errors are logged because the active node of the cluster has
reserved the shared virtual disk. The passive node periodically probes the shared
disk and receives a SCSI reservation conflict error.