Glossary

ballooning

A term describing dynamic changes to an instance’s memory while the instance is running that don’t require an instance reboot. Depending on the hypervisor and configuration, changes may be automatically initiated by the hypervisor (based on the memory usage of the node and instance), or may need to be initiated manually.

BE parameter

BE stands for backend. BE parameters are hypervisor-independent instance parameters, such as the amount of RAM/virtual CPUs allocated to an instance.

DRBD

A block device driver that can be used to build RAID1 across the network or across shared storage, while using only locally-attached storage.

HV parameter

HV stands for hypervisor. HV parameters describe the virtualization- specific aspects of the instance. For example, a HV parameter might describe what kernel (if any) to use to boot the instance or what emulation model to use for the emulated hard drives.

HVM

Hardware Virtualization Mode. In this mode, the virtual machine is oblivious to the fact that it is virtualized and all its hardware is emulated.

LogicalUnit

The code associated with an OpCode; for example, the code that implements the startup of an instance.

LUXI

Local UniX Interface. The IPC method over unix(7) sockets used between the CLI tools/RAPI daemon and the master daemon.

OOB

Out of Band. This term describes methods of accessing a machine (or parts of a machine) by means other than the usual network connection. Examples include accessing a remote server via a physical serial console or via a virtual console. IPMI is also considered OOB access.

OpCode

A data structure encapsulating a basic cluster operation; for example: start instance, add instance, etc.

PVM

(Xen) Para-virtualization mode. In this mode, the virtual machine is aware that it is virtualized; therefore, there is no need for hardware emulation or virtualization.

SoR

State of Record. Refers to values/properties that come from an authoritative configuration source. For example, the maximum VCPU over- subscription ratio is a SoR value, but the current over-subscription ratio (based upon how many instances live on the node) is a SoW value.

SoW

State of the World. Refers to values that directly describe the world, as opposed to values that come from the configuration (which are considered SoR).

tmem

Xen Transcendent Memory (http://en.wikipedia.org/wiki/Transcendent_memory). tmem is a mechanism used by Xen to provide memory over-subscription.

watcher

ganeti-watcher is a tool that should be run regularly from cron. The tool executes tasks such as restarting failed instances and restarting secondary DRBD devices. For more details, see the man page ganeti-watcher(8).