CA AppLogic® for System z abstracts the underlying hardware system by virtualizing hardware resources. It is the first system to make distributed web applications portable and hardware-independent. CA AppLogic® for System z achieves this by abstracting hardware into three distinct types of virtual resources: Virtual machines, virtual volumes and virtual network interfaces.
CA AppLogic® for System z sees the hardware system as a grid of computing or storage nodes connected with a Gigabit or faster network, where at least one node is acting as a grid controller. Each node provides up to three pools of virtual resources, one for each resource type. The controller aggregates the discrete resource pools into a single, scalable distributed resource pool. As a result, for each type of virtual resource there is one scalable, systemwide resource pool.
CA AppLogic® for System z allocates or creates virtual resources from their respective system pools. Each resource carries a systemwide identification. This enables CA AppLogic® for System z to access resources in a uniform fashion, no matter where on the grid they are actually located and to migrate resources transparently from one node to another without disrupting the running applications.
CA AppLogic® for System z implements virtual machines using z/VM. z/VM partitions a server logical partition (LPAR) into multiple virtual machines (VM). Each VM boots a separate operating system (for example, Linux), and runs any other software it may be configured with.
CA AppLogic® for System z virtualizes the access to two types of peripheral devices - network interface cards (NIC) and block storage devices.
In CA AppLogic® for System z, a virtual storage volume (also known as "virtual volume") is a logical disk consisting of one or more minidisks on the LPAR.
CA AppLogic® for System z virtual volumes are persistent, named objects. Their size is defined at the time they are created. They reside on the system until explicitly destroyed. In the current version of CA AppLogic® for System z, each individual virtual volume is a logical volume built on one or more minidisks owned by the non-bootable parking VM.
A typical virtual volume is accessed by a single virtual machine. Whenever a volume is shared by multiple VMs, the access to that volume is usually read-only. This enables CA AppLogic® for System z to cache most volumes.
CA AppLogic® for System z also makes it easy to create multiple instances of the same virtual volume. Those are useful whenever there is a need to share a large set of data among multiple VMs in a way that permits each VM to make relatively small modifications to the common set of data, such as configuration settings, bindings, and so on.
CA AppLogic® for System z uses virtual network interfaces to abstract the structure of the interconnection in the application.
A virtual network interface is a unique connection point within the CA AppLogic® for System z system. An instance of a virtual network interface can be attached to a virtual network interface card (vNIC) on the boundary of a virtual machine, effectively terminating all traffic through that vNIC.
A pair of virtual networks interfaces can be connected to form a virtual wire - a point-to-point connection that carries IP traffic between its endpoints independently of the underlying network technology. The virtual wire then becomes a logical equivalent of a crossover cable that connects two network interface cards directly: It transfers packets between the two vNICs.
Depending on the physical network used, CA AppLogic® for System z implements virtual wires by tunneling traffic through IP connections or as direct memory-to-memory transfer whenever both network interfaces happen to be on the same server. All of this is completely transparent to the communicating VMs.
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