HP virtualization
This section discusses
HP's Virtual Server Environment (VSE) as well as
vPars,
nPartitions, and
IVMs.
nPartitions offers true electrical isolation as well as cell granularity. nPartitions are based on hard partitions, which were first introduced by HP in 2000 and offer greater fault isolation than soft partitions. nPartitions let you service one partition while others are online, which is similar to IBM's logical partitioning, though systems require a reboot when moving cells from one partition to another. It's important to note that while
nPartitions support HP-UX, Windows®, VMS, and Linux, they only do so on their Itanium processor, not on their HP9000 PA Risc architecture. Partition scalability also depends on the operating system running in the nPartition. Another downside is that entry-level servers do not support this technology — only HP9000 and Integrity High End and Midrange servers. They also do not support moving resources to and from other partitions without a reboot.
vPars are separate operating system instances on the same nPartition or server. This offering lets you dynamically move either CPU or memory resources between partitions as the workload requirements change. They also give you the ability to run multiple copies of HP-UX on the same hardware. Using vPars, you can move CPUs to other running partitions, similar to PowerVM and the System p. What you can't do with vPars is share resources, because there is no virtualized layer in which to manage the interface between the hardware and the operating systems. This is one reason why performance overhead is limited, a feature that HP will market without discussing its clear limitations. The scalability is also restricted as to the nPartition that the vPar is created on, the max being an 8 cell limitation. There is also limited workload support; resources cannot be added or removed. Finally, vPars also don't let you share resources between partitions, nor can you dynamically allocate processing resources between partitions.
Integrity Virtual Machines (IVMs) are separate guest instances on the same nPartition with different operating system versions and users in a fully isolated environment. First introduced in 2005, they allow for a partition to have its own full copy of the operating system. Within this copy, the virtual machines share the resources. This is similar in many ways to IBM's PowerVM, as there is granularity for CPUs and I/O device sharing. The granularity actually beats PowerVM because you can have up to 1/20 of a micropartition; the System p allows for only 1/10 of a CPU. The downside here is scalability. With HP's virtual machines there is a 4 CPU limitation and RAM limitation of 64 GB. Reboots are also required to add processors or memory. There is no support for features such as uncapped partitions or shared processor pools. Finally, it's important to note that HP PA RISC servers are not supported; only Integrity servers are supported. Virtual storage adapters also cannot be moved, unless the virtual machines are shut down. You also cannot dedicate processing resources to a single partition.
Resource Partitions are created from the HP Process resource manager and allow resources for specific applications within a single operating system. This is also a resource management tool, which lets you manage CPU, memory, and disk bandwidth. It allows minimum allocations of CPUs, and even lets you cap a CPU by group. In many ways, this is similar to a Solaris container or AIX WPAR in that it lets you have several applications residing in one copy of HP-UX. This feature has been available since HP-UX 9.0.
