A
- XenCenter
The name of the XenServer client application, used to control one or more XenServer Hosts.
B
- BVT
The BVT scheduler is used to give proportional fair shares of the CPU to domains.
C
- CPU Weight
A parameter that can be set for virtual CPUs of VMs. Similar to traditional Linux schedulers that divide CPU time for user processes, Xen schedules resources between VMs. The CPU Weight parameter tell the scheduler how much priority to give that virtual CPU when dividing up resources.
D
- Domain
A domain is the execution context that contains a running virtual machine. The relationship between virtual machines and domains on Xen is similar to that between programs and processes in an operating system: a virtual machine is a persistent entity that resides on disk (somewhat like a program). When it is loaded for execution, it runs in a domain. Each domain has a domain ID.
- Dom0 (Domain 0)
The first domain to be started on a Xen machine. Dom0 has direct access to the hardware and is responsible for managing the allocation of system resources to unprivileged virtual machines (variously called DomUs, guests, and Virtual Machines).
- DomU (Domain U)
A generic name for a virtual machine running on a Xen Host, managed by Dom0. In XenServer, also called Virtual Machine.
- Domain ID
A unique identifier for a domain, analogous to a process ID in an operating system.
- dropbox
The directory where compressed operating system image files created by the P2V operation are copied to on the XenServer host.
F
- Fibre Channel
A gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards (INCITS), an American National Standard Institute–accredited standards committee. It started for use primarily in the supercomputer field, but has become the standard connection type for storage area networks in enterprise storage. Despite its name, Fibre Channel signaling can run on both twisted-pair copper wire and fiber optic cables.
- Full virtualization
An approach to virtualization which requires no modifications to the hosted operating system, providing the illusion of a complete system of real hardware devices.
H
- Hardware Abstraction Layer
A layer of software between the physical hardware of a computer and the operating system, driver, and application software that runs on that computer. Its function is to hide differences in hardware from most of the operating system kernel, so that less kernel-mode code needs to be changed to enable it to run on systems with different hardware. A HAL allows instructions from higher level computer languages to communicate with lower level components, such as directly with hardware.
Windows NT-based operating systems have a HAL in the kernel. This allows portability of the Windows NT kernel-mode code to a variety of processors, with different memory management unit architectures, and a variety of systems with different I/O bus architectures. Most of that code runs without change on those systems, when compiled for the instruction set for those systems. For example, Windows 2000 can run on different Intel architectures like SMP by using the appropriate HAL between the OS and the hardware.
- Host Bus Adapter
An interface that connects a host system (the computer) to other network and storage devices. The term is is most often used to refer to a Fibre Channel interface card.
- Hypervisor
An alternative term for a Virtual Machine Monitor - the software that allows multiple virtual machines to be multiplexed on a single physical machine. Used because it means "beyond supervisor," since it is responsible for managing multiple "supervisor" kernels.
I
- igroup
Short for initiator group, a logical named entity that is assigned to one or more addresses associated with one or more initiators.
- iSCSI
Internet SCSI (iSCSI) is a network protocol standard that allows the use of the SCSI protocol over TCP/IP networks. Acceptance of iSCSI in corporate production environments has accelerated now that Gigabit Ethernet is common. Building iSCSI-based Storage Area Networks (SAN) has become a less costly but worthy alternative to creating Fibre Channel-based SANs.
- ISO image
An informal term for a disk image of an ISO-9660 file system (CD-ROMs, DVD-ROMs, etc.). In addition to the data files that are contained in the ISO image, it also contains all the filesystem metadata (boot code, structures, and attributes). All of this information is contained in a single file. These properties make ISOs an attractive alternative to physical media for the distribution of software, as they are simple to retrieve over the Internet.
- iSCSI initiator
In an iSCSI SAN, the initiator creates a virtual device node on the local host and redirects all IO requests over a TCP connection to the remote target.
- iSCSI target
In an iSCSI SAN, the target is the device that hosts the actual block device, called a LUN (Logical Unit Number); for example, a locally attached SCSI drive.
J
- Java Runtime Environment
A subset of Sun's Java Development Kit (JDK) that contains the core executables and files that constitute the standard Java platform. The JRE includes the Java Virtual Machine (JVM), core classes, and supporting files.
K
- kickstart file
With the kickstart installation method (invented by red Hat), a system administrator can create a single file containing the answers to all the questions that would normally be asked during a typical Red Hat Linux installation.
L
- libvirt
Libvirt is a C toolkit providing interaction with the virtualization capabilities of Linux operating. The libvirt project can be found on the Web at http://www.libvirt.org/. The goal of libvirt is to provide the lowest possible generic and stable layer to manage VMs running on a machine. Its original aim was to provide a long term, stable C API for Xen.
- License key
A unique key code generated for product validation.
- Live Relocation
A technique for moving a running virtual machine to another physical host, without stopping it or the services running on it.
- Logical Volume Group
Taken collectively, the collection of logical volumes and the disk devices on a XenServer Host, also called a Storage Repository (SR). In addition to the logical volumes that represent the virtual disks of the VMs, there is a metadata volume group, which contains the VM configuration data. A LOgical Volume Group, then, contains one or more VM with their virtual disks and configuration files in a single entity.
- Logical Volume Management
In computer storage, a method of allocating space on mass storage devices that allows greater flexibility than conventional partitioning schemes. In particular, a logical volume manager can concatenate, stripe together or otherwise combine partitions into larger virtual ones that can be resized or moved, possibly while they are being used.
- LUN
In computer storage, a LUN (logical unit number) is an address for an individual disk drive and, by extension, the disk device itself. The term is used in the SCSI protocol as a way to differentiate individual disk drives within a common SCSI target device like a disk array. The term has become common in storage area networks (SANs) and other enterprise storage technologies. LUNs are normally not entire disk drives but rather virtual partitions (or volumes) of a RAID set.
M
- MAC address
Acronym for Media Access Control address. In computer networking, a MAC address is a unique identifier attached to most network interface controllers (NICs). It is a number that acts like a unique name for a particular network adapter.
N
- Network address translation
A process that re-writes the source and/or destination addresses of IP packets as they pass through a router or firewall. It is useful for enabling multiple hosts on a private network to access the Internet using a single public IP address, and for routing packets to multiple servers behind a single IP address.
- Network interface controller
A computer hardware device designed to allow computers to communicate over a network. It is both an OSI layer 1 (physical layer) and layer 2 (data link layer) device, as it provides physical access to a networking medium and provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or via wireless technology.
N
- Quality of Service
Refers to control mechanisms in a packet-switching network that can provide different priority to different users or data flows, or guarantee a certain level of performance to a data flow, in accordance with requests from the application program. QoS guarantees are important if the network capacity is limited, especially for real-time streaming multimedia applications, for example voice over IP and IP-TV, since these often require fixed bit rate and may be delay sensitive.
The term Quality of Service is sometimes used as a quality measure with many alternative definitions, rather than referring to the control mechanisms. In computer networking, a good QoS may mean advanced QoS mechanisms, or high probability that the network is able to provide the requested level of performance. High QoS is often confused with a high level of performance, for example high bit rate, low latency and low bit error probability.
P
- Paravirtualization
A virtualization technique that presents the abstraction of virtual machines with a software interface that is similar but not identical to that of the underlying hardware. This requires operating systems to be explicitly ported to run on top of the virtual machine monitor or hypervisor, but enables the virtual machines that run on it to achieve near-native performance.
- Paravirtualized device drivers
Hardware virtualization support in Intel VT and AMD-V CPUs allows Xen to run unmodified operating systems like Windows. In this context, paravirtualization of device driver software reduces the number of interactions between the guest operating system and the hypervisor, resulting in better performance (higher throughput, lower latency, reduced CPU utilization) compared to device emulation, allowing Windows VMs to achieve similar performance to paravirtualized Linux operating systems.
- Physical Address Extension
A means of allowing up to 64 gigabytes of memory to be addressed in 32 bit systems, given appropriate operating system support. PAE is provided by Intel Pentium Pro and above CPUs (including all Pentium-series processors except the original Pentium and the Pentium MMX), as well as by some compatible processors such as those from AMD. The CPUID flag PAE is assigned for the purpose of identifying CPUs with this capability.
- Physical to Virtual Conversion
The process by which a running physical instance of a server and its filesystem, applications, etc., are converted to a form that can be instantiated as a virtual machine.
- Preboot Execution Environment
An environment to boot computers using a network interface card independently of available local data storage devices (like hard disks, floppy drives or CD-ROM drives) or installed operating systems.
R
- Remote Desktop Protocol
A multi-channel protocol, based on the ITU T.share protocol (also known as T.128), that allows a user to connect to a computer running Microsoft Terminal Services. Clients exist for most versions of Windows, and other operating systems such as Linux, FreeBSD, and Mac OS X.
- Resource Pool
a single managed entity comprised of multiple XenServer Host installations, bound together to collectively host Virtual Machines. When combined with shared storage, a Resource Pool enables VMs to be started on any XenServer Host which has sufficient memory and then dynamically moved between XenServer Hosts while running with minimal downtime (XenMotion). If an individual XenServer Host suffers a hardware failure then the system administrator can restart the failed VMs on another XenServer Host in the same Resource Pool. The XenServer Hosts in a Resource Pool must be homogeneous and must have static IP addresses.
S
- Shadow pagetables
A technique for hiding the layout of machine memory from a virtual machine's operating system. Used in some VMMs to provide the illusion of contiguous physical memory, in Xen this is used during live migration.
- Storage Area Network
A network designed to attach computer storage devices such as disk array controllers and tape libraries to servers. Currently SANs are most commonly found in enterprise environments. A SAN allows a machine to connect to remote targets such as disks and tape drives on a network for block level I/O. The devices essentially appear as locally attached devices to drivers and application software.
- Storage Manager
The subsystem on the XenServer Host which deals with all storage repository management. The Storage Manager is an abstraction layer for storage that is incorporated into XenServer beginning with version 3.1. Disks are referenced as an abstract disk container called a Virtual Disk Image (VDI). The Storage Manager handles the layout and organization of the actual VDI containers on the individual storage substrates such as local host managed LVM partitions, NFS-mounted disk images, or Fibre Channel SANs.
- Storage Repository
Taken collectively, the collection of logical volumes and the disk devices on a XenServer Host, also called a Logical Volume Group. In addition to the logical volumes that represent the virtual disks of the VMs, there is a metadata volume group, which contains the VM configuration data. A Storage Repository, then, contains one or more VM with their virtual disks and configuration files in a single entity.
- Symmetric Multiprocessing
A computer architecture that provides fast performance by making multiple CPUs available to complete individual processes simultaneously (multiprocessing). Unlike asymmetrical processing, any idle processor can be assigned any task, and additional CPUs can be added to improve performance and handle increased loads.
T
- Template
A "gold image" which contains all the various configuration settings to instantiate a specific VM. XenServer ships with a base set of Templates, which range from generic "raw" VMs that can boot an OS vendor installation CD (Windows) or run an installation from a network repository (Red Hat Enterprise Linux, SUSE Linux Enterprise 10) to complete pre-configured OS instances (Debian Etch and Sarge).
- Trivial File Transfer Protocol
Trivial File Transfer Protocol (TFTP) is a very simple file transfer protocol, with the functionality of a very basic form of FTP. A tftp server is used to enable PXE booting.
U
- UUID
Acronym for Universally Unique Identifier, an identifier standard used in software engineering, standardized by the Open Software Foundation (OSF) as part of the Distributed Computing Environment (DCE). The intent of UUIDs is to enable distributed systems to uniquely identify information without significant central coordination.
V
- Virtual block device
Persistent storage available to a virtual machine, providing the abstraction of an actual block storage device. VBDs may be actual block devices, filesystem images, or remote/network storage.
- Virtual Bridge
A virtual network bridge or switch is a software version of a standard network switch, which is used to tie two or more networks together. Xen uses virtual bridges to attach the virtual network interfaces in Virtual Machines to a physical network interface on the Xen host computer.
- Virtual CPU
The virtual CPU executes the instruction streams of virtual machines, emulates privileged instructions, exposes virtual interrupts, and handles virtual programmed I/Os. The virtual CPU also exposes a number of purely virtual registers.
- Virtual Disk Image
An abstract disk container in XenServer. The layout and organisation of the VDI containers on individual storage substrates such as local host managed LVM partitions, NFS-mounted disk images, or Fibre Channel SANs, is handled by the Storage Manager subsystem.
- Virtual Hard Disk
The Microsoft VHD file format specifies a virtual machine hard disk that can reside on a native host file system encapsulated within a single file. The format is used by Microsoft Virtual PC 2004 and Virtual Server 2005, and the format will be used by the Viridian version of Microsoft Windows Server that will include hypervisor-based virtualization technology. Beyond that, the VHD format is broadly applicable, because it is agnostic to the virtualization technology, host operating system, or guest operating system with which it is used.
- Virtual Machine
The environment in which a hosted operating system runs, providing the abstraction of a dedicated machine. A virtual machine may be identical to the underlying hardware, as in full virtualization, or it may differ, as in paravirtualization.
- Virtual Machine Disk
The VMware Virtual Machine Disk format specifies a virtual machine hard disk that can reside on a native host file system encapsulated within a single file. Similar to the Microsoft VHD format.
- Virtual Machine Monitor
The hypervisor - the software that allows multiple virtual machines to be multiplexed on a single physical machine.
- Virtual to Virtual Conversion
The process by which a virtual machine of one type and its filesystem, applications, etc., are converted to a form that can be instantiated as a virtual machine of another type.
X
- Xen
Xen is a high-performance, open source paravirtualizing virtual machine monitor, developed primarily by the Systems Research Group at the University of Cambridge Computer Laboratory.
- XenServer Host
The name of a Xen host in the context of XenServer product family.
- Xen host
The physical server used to run a Xen Dom0 and some number of virtual machines. In XenServer, XenServer Host fills this role.
- XenLinux
Official name for the port of the Linux kernel that runs on Xen.
- Virtual Machine
In the context of the XenServer product family, a generic name for a virtual machine running on a XenServer Host.
posted by foundage @ 3:47 AM
0 comments
links to this post
