Ensuring Integrity When Sharing DASD Under z/VM › Serializing Access in z/VM Environments

Serializing Access in z/VM Environments

The type of reserve/release processing that you need depends on whether you have several real processors, several guest systems, or a combination of both.

• Real reserve/release processing serializes access among different real processors; that is, systems that are not running under the same z/VM operating system.
• Virtual reserve/release processing serializes access among guest systems running under the same z/VM operating system.

Use both real and virtual reserve/release processing if you have several guests running under one z/VM operating system and you have at least two real processors in your complex.

A crucial difference between real and virtual reserve/release is that real reserve/release restricts access to an entire device (or pack), while virtual reserve/release restricts access to a minidisk. A minidisk is an addressable unit of storage on a device. If you define the entire device as a single minidisk, then you create a full-pack minidisk. You can also partition a device into several minidisks.