Operating Systems

Power systems virtualization enabled by IBM PowerVM provides a variety of storage virtualization options, including the Virtual I/O Server (VIOS), a special-purpose virtual machine that provides virtual I/O resources to client partitions in the form of virtualized storage or virtual networking. The VIOS owns the physical and logical I/O resources shared with clients. A physical I/O resource assigned to a VIOS can be shared by one or more Virtual Machines (VMs). 

VIOS facilitates the sharing of physical devices among VMs. It comes packaged with PowerVM and has been well-received since its introduction in 2004. It has been widely deployed by mid-size and large enterprises, and smaller organizations have also implemented it, especially with the introduction of PowerLinux-focused virtualization offerings.

When it comes to virtualized storage, Power is rich and getting richer with ongoing enhancements. The VIOS server provides the core facilities for two storage virtualization models, virtual SCSI (vSCSI) and N_Port ID Virtualization (NPIV). vSCSI has been extended into a distributed capability called Shared Storage Pools (SSP), or next-generation vSCSI. All three address the challenges of storage virtualization and each option comes with a partially overlapping set of capabilities (see Figure 1). The PowerVM customer must determine which solution best fits their enterprise’s requirements.

“Many PowerVM customers end up using a combination,” notes Thomas Bosworth, IBM’s PowerVM offering manager.

vSCSI is PowerVM’s storage virtualization. vSCSI enables pooling of heterogeneous storage into a homogeneous set of storage that’s then allocated to client VMs in the form of generic SCSI Logical Unit Numbers (LUNs). The VIOS performs SCSI emulation and acts as the SCSI target.

NPIV, another virtual storage option for adapter sharing, provides direct access to Fibre Channel (FC) adapters from multiple client partitions, simplifying management of FC Storage Area Network (SAN) environments. Specifically, virtual FC Host Bus Adapters (HBAs) are created with unique World Wide Port Names (WWPNs) and routed through a physical FC HBA. This enables multiple virtual servers to share a single physical port. With NPIV, the VIOS facilitates physical adapter sharing; there’s no device-level abstraction or emulation. Rather than acting as a storage virtualizer, VIOS operates as a pass-through, extending a Fibre Channel Protocol (FCP) connection from the client VM to the SAN. 

SSP is vSCSI storage virtualization that’s coordinated across multiple VIOSs that can span multiple Power frames. In effect, the LUN is available on all the VIOSs. The benefit of a single pool of storage that spans multiple frames is location transparency; a VM or its storage can be moved around more freely, without regard for where the physical resources reside. This simplifies the SAN administration required for Live Partition Mobility (LPM). SSP also offers some advanced storage services that make cloning Logical Partitions (LPARs), disk snapshots, rapid provisioning, and thin provisioning possible. These capabilities can provide better utilization, agility, and simplification.

vSCSI, SSP, and NPIV support are included with PowerVM Express, Standard, and Enterprise editions for AIX, Linux, and IBM i VM partitions on all POWER6 and POWER7 processor-based servers, including blades.

Power Virtual I/O Benefits

Virtualized I/O storage on the Power platform delivers clear benefits, including:

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