Glossary
General
| Term | Meaning | Definition |
|---|---|---|
| CPU | Central Processing Unit | Processor. |
| OS | Operating System | Software environment running on a VM or physical machine. |
Core infrastructure
| Term | Meaning | Definition |
|---|---|---|
| Dom0 | Control domain | The privileged Linux VM started with each host: it runs XAPI and the storage/network drivers. Its resources are shared by all operations on the host. |
| Host | A hypervisor server (XCP-ng / XenServer node) in the pool. | |
| PBD | Physical Block Device | Binds an SR to a host (how the host reaches that storage). |
| PIF | Physical Interface | A physical NIC on a host, used for management, storage, or guest networks. |
| Pool | A set of hosts sharing storage and network configuration. | |
| Pool master | The host that coordinates the pool and exposes its XAPI: XO always talks to the pool through its master. | |
| SR | Storage Repository | A storage container (local LVM, NFS, iSCSI, etc.) where VDIs live. Not to be confused with a backup repository (BR). |
| VBD | Virtual Block Device | The attachment that connects a VDI to a VM (device number, bootable flag, mode). |
| VDI | Virtual Disk Image | A virtual disk object on an SR (root disk, data disk, ISO, snapshot disk, etc.). Not to be confused with Virtual Desktop Infrastructure. |
| VIF | Virtual Network Interface | A virtual NIC on a VM, connected to a network. |
| VM | Virtual Machine | A guest machine (OS + virtual hardware) managed by the pool. |
Virtualization modes & hardware
| Term | Meaning | Definition |
|---|---|---|
| GPU | Graphics Processing Unit | Physical graphics hardware on a host. |
| HVM | Hardware Virtual Machine | Full hardware-emulated guest (typical for Windows and many Linux installs). |
| PGPU | Physical GPU | A physical GPU as seen by XAPI (grouping / passthrough context). |
| PV / PVM | Paravirtualization | Guest uses paravirtualized drivers/interfaces (legacy Linux style on Xen). |
| vCPU | Virtual CPU | A virtual processor presented to the VM. |
| vGPU | Virtual GPU | A virtual GPU slice assigned to a VM. |
| VTPM | Virtual Trusted Platform Module | Software TPM device exposed to a VM (e.g. Windows 11 / BitLocker). |
Networking & storage
| Term | Meaning | Definition |
|---|---|---|
| iSCSI | Internet Small Computer System Interface | Block SR backed by an iSCSI LUN. |
| ISO SR | ISO Storage | SR type used to store .iso images for VM install media. |
| LVM | Logical Volume Manager | Local volume-style SR (e.g. on host disks). |
| MTU | Maximum Transmission Unit | Largest Ethernet payload size on a link (e.g. jumbo frames). |
| NBD | Network Block Device | Protocol XO uses to read disk data directly from hosts, for faster NBD-enabled backups. Required for incremental backups of QCOW2 disks. |
| NFS | Network File System | File-based SR backed by an NFS export. |
| QCOW2 | QEMU Copy On Write v2 | Disk format lifting the 2 TiB VHD limit (up to 16 TiB per disk), generally available since XO 6.5 and recent XCP-ng releases. |
| SR-IOV | Single Root I/O Virtualization | Passing a virtual function of a physical NIC to a VM for near-native I/O. |
| Traffic rules | Firewall-like rules applied to networks and VIFs through the SDN controller. | |
| VHD | Virtual Hard Disk | Historical disk and backup format of the platform, limited to 2 TiB per disk (see QCOW2). |
| VLAN | Virtual LAN | Logical LAN segment; often tied to PIF tagging in XAPI. |
| XVA | XenServer Virtual Appliance | Archive format for a complete VM export, used by full backups. |
High availability & operations
| Term | Meaning | Definition |
|---|---|---|
| HA | High Availability | Pool feature to restart VMs elsewhere if a host fails (policy-driven). |
| RPU | Rolling Pool Update | XO-orchestrated update of a whole pool: hosts are patched and rebooted one by one while VMs are live migrated, with no VM downtime. |
Backup & replication
| Term | Meaning | Definition |
|---|---|---|
| BR | Backup Repository | Storage where XO writes backups (NFS, SMB, S3, local...), formerly called a "remote". See backup repositories. |
| CBT | Changed Block Tracking | XCP-ng/XenServer feature letting XO purge snapshot data: the reference snapshot keeps only small metadata on the SR. |
| Coalesce | The storage process merging a VDI chain after a snapshot is deleted. Backups create and delete snapshots, so coalesce health directly affects them. | |
| CR | Incremental replication | Regularly replays deltas of a VM to an SR on another pool or host, formerly "continuous replication". See incremental replication. |
| DR | Full replication | Regularly streams a full copy of a VM to an SR on another pool or host, formerly "disaster recovery". See full replication. |
| Full backup interval | Also called key backup interval: forces a periodic new full (key) backup in an incremental backup job. | |
| GFS | Grandfather-Father-Son | Long-term retention strategy keeping daily, weekly, monthly and yearly backups. |
| Health check | Automatic restore test after a backup: XO boots the restored VM to verify the backup is actually usable. | |
| Immutability | Protection making backups unmodifiable for a configured duration, even by XO itself (ransomware protection). | |
| Mirror backup | A backup of your backups: copies the archives of one BR to another, the key to 3-2-1 strategies. | |
| [NOBAK] | Marker added to a VDI name to exclude that disk from all backup jobs. | |
| Rolling snapshot | Scheduled automatic snapshots with retention. Snapshots live on the same SR as the VM: not a real backup. | |
| Sequence | Chains backup schedules so they run one after the other instead of competing in parallel. | |
| Smart backup | Selects VMs by criteria (pool, tags, power state) resolved at job runtime, instead of a fixed VM list. |
XCP-ng/Xen Orchestra-specific
| Term | Meaning | Definition |
|---|---|---|
| Guest tools | Drivers and agent installed inside a VM: they report the IP address and metrics, and enable clean shutdown and migration. | |
| V2V | Virtual to Virtual | Built-in migration tool importing VMs directly from VMware/ESXi to XCP-ng. |
| XAPI / xapi | Xen API | The management API and service on each host that XO talks to. |
| XCP-ng | The open source, Xen-based hypervisor managed by XO, developed by Vates alongside Xen Orchestra. | |
| XO | Xen Orchestra | The management UI/API stack (xo-server, xo-web, etc.). |
| XO 5 / XO 6 | The two web interfaces served by the same XO backend: XO 6 is the current default, XO 5 the previous generation. See XO 6 vs XO 5. | |
| XO Lite | Lightweight web UI embedded in every XCP-ng host (8.3+): basic management and XOA deployment, no installation needed. | |
| XO Proxy | Component deployed close to remote infrastructure to run backups locally, without streaming all data through the main XOA. | |
| XOA | Xen Orchestra Appliance | Prebuilt VM image that runs XO as a packaged appliance. |
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