Device compatibility in a Virtual I/O Server environment

Learn more about virtual-to-physical device compatibility in a Virtual I/O Server environment.

The virtual-to-physical device (p2v) compatibility described in this topic refers only to the data on the device, not necessarily to the capabilities of the device. A device is p2v compatible when the data retrieved from that device is identical regardless of whether it is accessed directly through a physical attachment or virtually (for example, through the Virtual I/O Server). That is, every logical block (for example, LBA 0 through LBA n-1) returns identical data for both physical and virtual devices. Device capacity must also be equal in order to claim p2v compliance. You can use the Virtual I/O Server chkdev command to determine if a device is p2v compatible.

Virtual disk devices exported by the Virtual I/O Server are referred to as virtual SCSI disks. A vitual SCSI disk device may be backed by an entire physical volume, a logical volume, a multi-path device, or a file.

Data replication (such as copy services) and device movement between physical and virtual environments are common operations in today's datacenter. These operations, involving devices in a virtualized environment, often have a dependency on p2v compliance.

Copy Services refer to various solutions that provide data replication function including data migration, flashcopy, point-in-time copy, and remote mirror and copy solutions. These capabilities are commonly used for disaster recovery, cloning, backup/restore, and more.

Device movement between physical and virtual environments refers to the ability to move a disk device between physical (for example, a direct-attached SAN) and virtual I/O (for example, . Virtual I/O Server-attached SAN) environments and use the disk without having to backup or restore the data. This capability is very useful for server consolidation.

The operations above may work if the device is p2v compatible. However, not all device combinations and data replication solutions have been tested by IBM®. See claims by the Copy Services vendor for support claims for devices managed by Virtual I/O Server.

A device is p2v compatible if it meets the following criteria:

• It is an entire physical volume (for example, a LUN)
• Device capacity is identical in both physical and virtual environments
• The Virtual I/O Server is able to manage this physical volume using a UDID or iEEE ID. For more information, see the Determining if a physical volume is managed by UDID or iEEE topic below.

Devices managed by the following multipathing solutions within the Virtual I/O Server are expected to be UDID devices.

• All multipath I/O (MPIO) versions, including Subsystem Device Driver Path Control Module (SDDPCM), EMC PCM, and Hitachi Dynamic Link Manager (HDLM) PCM
• EMC PowerPath 4.4.2.2 or later
• IBM Subsystem Device Driver (SDD) 1.6.2.3 or later
• Hitachi HDLM 5.6.1 or later

Virtual SCSI devices created with earlier versions of PowerPath, HDLM, and SDD are not managed by UDID format and are not expected to be p2v compliant. The operations mentioned above (for example, data replication or movement between Virtual I/O Server and non-Virtual I/O Server environments) are not likely to work in these cases.

• Determining whether a physical volume is managed by UDID or IEEE
  Determine whether a physical volume is or can be managed by a unit device identifier (UDID) or IEEE. You can use the Virtual I/O Server chkdev command to display this data.