VM Parallel Access Volumes Support

z/VM provides support for the IBM Parallel Access Volumes (PAV) feature of IBM DASD subsystems. PAVs enable a single System z server and applicable storage controllers to simultaneously process multiple I/O operations to the same logical volume, which can help to significantly improve I/O response times by reducing device queueing delays.

• On April 27, 2006, IBM announced the plan to support Parallel Access Volumes (PAVs) as minidisks
  Read about this new z/VM V5.2 support of PAV
• Read about the initial PAV support for z/VM V5.2 systems without the new support, and for systems prior to z/VM V5.2
• On Feb. 6, 2007, IBM announced HyperPAV Support on z/VM

What is PAV ?
Before the introduction of PAV, the terms “volume” and “subchannel” were frequently used interchangeably when discussing DASD architectures. With the introduction of PAV, a “volume” is more narrowly defined as a named collection of DASD cylinders that contain data, and “subchannels are envisioned as controlling virtual disk access mechanisms for the DASD volume. Each subchannel has a unique subchannel number and device number.

With PAV, a real DASD volume is accessed through a base subchannel and one or more alias subchannels. Although sometimes misleading, the base subchannel's device number identifier is used in many contexts to refer to the “volume” as well. This is a holdover from the widely-accepted practice of referring to volumes with a six-character volume serial number and a “subchannel device number”interchangeably when a one-to-one correspondence existed.

Today, a PAV volume has one volume serial number and multiple subchannels.

Continue on to the z/VM V5.2 support of PAV.