Glossary
Advanced Host Controller Interface
A standard interface mode for disk controllers that allows storage devices to communicate with your computer. In Unraid, AHCI mode is typically recommended for better compatibility.
Allocation Method
A setting that controls how Unraid chooses which array disk to place new files on when using user shares. Options include High-Water (balanced distribution), Fill-Up (sequential filling), and Most-Free (prioritizes emptiest disk).
AMD Virtualization
A feature in AMD processors that enables virtualization support. This feature must be enabled in your computer's BIOS settings before you can create virtual machines in Unraid.
apcupsd Protocol
Protocol used by Unraid to communicate with UPS devices. Enables graceful shutdowns during power failures.
Apollo Sandbox
A development tool for testing and exploring GraphQL APIs used in Unraid's development environment.
Apple Filing Protocol
A network protocol for macOS file sharing in Unraid. No longer used by Apple, and support was removed in Unraid 6.9. Instead, see "SMB" for modern macOS compatibility.
Application Server
One of Unraid’s core functions where it can run containerized applications (like Plex, Sonarr, etc.) directly on the system without requiring a full virtual machine.
Array
The collection of data disks managed by Unraid, which can include parity protection. The array is Unraid's main storage system, storing data across multiple devices.
AWS Cognito OAuth Server
An Amazon Web Services authentication service that Unraid Connect uses to manage user identities and access securely.
Bit Rot
The theoretical degradation of disk data over time. File systems like BTRFS and ZFS can detect errors, but practical occurrence rates are debated.
BTRFS
“B-Tree File System,” a modern file system option in Unraid that supports features like snapshots and checksumming. Often used for cache pools due to its ability to detect corruption.
Cache
A feature in Unraid that temporarily stores newly written data on faster drives (typically SSDs) before moving it to the array, improving write performance.
Cache Pool
High-speed storage for temporary data. Pools can be single-disk or multi-disk. The Mover process transfers data to/from array periodically.
See RAID - Wikipedia
Checksum
A small piece of data generated from a larger block of data, used to detect errors during storage or transmission. BTRFS and ZFS file systems use checksums to verify data integrity.
CPU Pinning
The process of assigning specific CPU cores to VMs or Docker containers. This improves performance by ensuring that critical applications have dedicated processing resources.
CRC
“Cyclic Redundancy Check,” an error-detecting code used to identify data corruption during storage or transmission.
CRC Errors
Error messages generated when a CRC check fails. Cyclic Redundancy Check errors often indicate cabling issues rather than disk failures, so be sure to check your SATA cable connections.
Deep Linking
A feature in Unraid Connect that allows direct navigation to specific pages within your Unraid server’s webGUI.
DMI
“Desktop Management Interface,” a framework that provides system information about hardware components. Unraid uses this to identify system specifications.
DNS name resolution
Process of converting domain names (e.g., www.wikipedia.com) to IP addresses. Configured via router or custom DNS settings.
DNS rebinding
Security feature that must be disabled in your browser/DNS server for your server to work with myunraid.net URLs.
Emulated disk
Virtual disk created when a physical drive fails. Uses parity + remaining array drives to emulate the missing drive. The failed drive must be replaced before another one fails.
FTP
“File Transfer Protocol,” an unencrypted file transfer protocol. Not recommended - use SFTP or SMB for secure transfers.
Go Link
A permanent, short URL format used in Unraid documentation that redirects to current content locations, ensuring links remain valid even as documentation is reorganized.
GPU passthrough
A technique that gives a virtual machine direct control over a physical graphics card, providing near-native performance for graphics-intensive applications like gaming.
GraphQL
A query language and runtime for APIs used in Unraid Connect, allowing efficient data retrieval with a single request.
Guest agent
A software component installed inside a virtual machine that enables better communication between the VM and the Unraid host system.
GUID
“Globally Unique Identifier,” a unique reference number for identifying hardware devices or software components. Each Unraid USB flash drive has a unique GUID that is used for licensing.
See GUID - Wikipedia
Hash
A mathematical function that converts data into a fixed-size string of characters, used in Unraid for password storage and file integrity verification.
Hashed passwords
Passwords processed through a cryptographic hash function for secure storage in Unraid, making them difficult to reverse engineer.
HBA mode
A configuration setting for storage controllers where they function as direct pass-through devices rather than RAID controllers, recommended for optimal Unraid performance.
HVM
“Hardware Virtual Machine,” a virtualization approach that uses CPU hardware capabilities to run unmodified guest operating systems. Required for virtual machines in Unraid.
Hypervisor
Software that creates and manages virtual machines. Unraid functions as a type 2 hypervisor, running on top of the Linux kernel.
I440fx
A legacy chipset emulation for virtual machines. Generally used for older operating systems and compatibility scenarios when Q35 isn’t suitable.
Included or excluded disks
Disks explicitly added to or removed from a share. Included disks are an active part of the share, while excluded disks are excluded from automatic file allocation.
Intel VT-X
“Intel Virtualization Technology for Directed I/O,” Intel’s hardware virtualization capability enabling VMs to run operating systems directly on the CPU. Essential for VM performance in Unraid on Intel platforms. (AMD equivalent - AMD-V)
IOMMU
“Input/Output Memory Management Unit,” a security feature that isolates virtual machines (VMs) from direct hardware access, preventing unauthorized data access. Ensures VMs only interact with assigned hardware.
JBOD
“Just a Bunch Of Disks,” disks configured as standalone devices without RAID. Each disk operates independently, with no redundancy.
See JBOD - Wikipedia
Keypair
A pair of cryptographic keys (public/private) used for secure SSH access. The public key is shared, while the private key remains confidential.
KVM
“Kernel-based Virtual Machine,” Linux’s native virtualization solution used by Unraid to run VMs. Provides direct hardware access for high performance.
libvirt
The virtualization API and management tool that Unraid uses to create and manage virtual machines.
Linux FUSE
“Filesystem in Userspace,” a framework for directly mounting virtual file systems (e.g., SSHFS) in user space, enabling flexible file access.
LUKS
“Linux Unified Key Setup,” a disk encryption system for securing data on Unraid. Encrypts entire drives to protect against unauthorized access.
MagicDNS
A Tailscale-specific dynamic DNS service that automatically updates your Unraid server’s domain name with its current IP address. To demonstrate, it would allow a computer at "desktop.yourtailnet.ts.net" to find another machine, "tower.yourtailnet.ts.net", even if they were in different physical locations.
MAID
“Massive Array of Idle Disks,” an energy-saving strategy where drives spin down when idle. Requires careful configuration to avoid data loss.
Maintenance mode
Feature that starts the array without mounting drives. Enables disk repair, re-assignment, or parity rebuilds without affecting the array's active data.
mDNS
A networking protocol that allows your local computer to resolve "tower.local" even though there is no actual DNS server configured to resolve that name. Only works on the ".local" top-level domain, which is why Unraid uses it by default. Only resolves successfully when the client and server are on the same subnet.
See Multicast DNS
Memory ballooning
A VM feature that dynamically adjusts allocated RAM based on host system needs. Prevents VMs from monopolizing memory.
Mirror (root profile)
A RAID 1 configuration for the root partition, providing redundancy for critical system files.
Mover
Transfers data between the primary and secondary storage defined for a share in either direction during scheduled runs.
MTU
“Maximum Transmission Unit,” the largest size of data packet that can be transmitted over a network interface. Recommended to keep default and avoid jumbo frames.
See /termlink/ and Maximum Transmission Unit - Wikipedia
Multi-device pool
A cache configuration using multiple drives (often in RAID 1/10) to balance speed and redundancy.
Multiple-device mirror
A RAID 10 setup for the cache pool, combining mirroring and striping for optimal performance and redundancy.
Myunraid.net certificate
A security certificate issued by Unraid Connect for secure access to your server's webGUI.
NAT
“Network Address Translation,” a network technique that allows multiple devices on a private network to share a single public IP address.
NFS
“Network File System,” a protocol for sharing files across a network, enabling remote systems to access files as if they were local.
NIC bonding
(Advanced) Combines network interfaces for redundancy/bandwidth. Requires compatible switch configuration. (Avoid triggering if unfamiliar.)
NIC bridging
A VM networking mode where the VM shares the host’s physical network interface for direct internet access.
OpenVPN
A secure VPN protocol used to create encrypted connections to your Unraid server from remote locations.
OVMF
“Open Virtual Machine Firmware,” firmware for UEFI-based VMs, enabling features like Secure Boot. Required for modern OS installations.
Parity
A redundancy mechanism that protects data against disk failures by storing a checksum across the array.
Parity check
A background process that verifies data integrity across the array, ensuring parity is up-to-date.
Parity drives
Redundant drives in the array that maintain parity information to recover data during disk failures.
Parity Swap
Three-drive procedure for when you must replace a data drive while upgrading your parity drive to one with a larger capacity.
PME Event
“Power Management Event,” a system log entry indicating a hardware power-related issue (e.g., USB disconnection).
Primary storage
The main location where data is initially written (cache) before Mover moves it to secondary storage (array).
Public bridge
A VM networking mode where the VM obtains its own IP address on the host’s network, visible to other devices.
PuTTY
A free SSH client for Windows used to access Unraid’s terminal interface remotely.
Q35
A modern chipset emulation mode for VMs, offering better compatibility with newer operating systems.
QEMU
A hardware emulator used by Unraid to run x86/x64 VMs. Handles CPU, memory, and I/O virtualization.
See QEMU - Wikipedia
RAID
“Redundant Array of Independent Disks,” a storage technology combining multiple drives for performance, redundancy, or both.
RAID 0
Striping – A RAID configuration that splits data across drives for faster read/write speeds but offers no redundancy.
RAID 1
Mirroring – A redundancy method that duplicates all data across two or more drives. If one drive fails, another contains an exact copy of the data.
RAID 10
Striped Mirrors – A combination of RAID 1 (mirroring) and RAID 0 (striping) that balances speed and redundancy. Data is striped across mirrored pairs, providing performance and protection against drive failures.
RAID 5
A storage method that distributes data and parity information across three or more drives. Traditional RAID 5 stripes data across all drives, unlike Unraid which keeps complete files on individual disks.
RAID 6
Similar to RAID 5 but with dual parity, allowing the array to survive two simultaneous drive failures.
RAIDZ1
ZFS’s implementation of RAID 5, offering single-parity protection with data checksumming for corruption detection.
RAIDZ2
ZFS’s implementation of RAID 6, providing dual-parity protection with data checksumming, allowing survival of two simultaneous drive failures.
RAIDZ3
ZFS’s triple-parity implementation, allowing the array to survive three simultaneous drive failures. Useful for very large arrays.
Read check
A process that verifies data can be read from a drive without comparing it to parity. Useful for testing drive health without full parity check overhead.
Reallocated sectors
Bad sectors on a drive that have been replaced with spare sectors. A rising count in SMART reports indicates drive degradation and potential failure.
Root profile
The vdev (virtual device) configuration for the root pool in ZFS, typically set as a mirror for redundancy of system files.
Root user
The administrator account in Unraid with full system access and permissions. Similar to the Administrator account in Windows.
Root vDev
The primary virtual device in a ZFS pool configuration, defining how data is distributed and protected across physical drives.
SAMBA
An implementation of the SMB protocol that allows Unraid to share files with Windows, macOS, and Linux systems.
Scheduled Mover process
An automated task that transfers files from a pool to another array or pool in either direction, balancing performance with data protection.
Scrub
A background maintenance process that checks file system integrity, verifies checksums, and repairs corrupted data when possible (used with BTRFS and ZFS).
SeaBIOS
A legacy BIOS implementation used for virtual machines in Unraid. Generally used for older operating systems that don’t support UEFI.
SMART
“Self-Monitoring, Analysis, and Reporting Technology,” a monitoring system built into hard drives that reports on various reliability indicators to help predict drive failures.
SMART polling
The frequency at which Unraid checks the SMART status of drives. More frequent polling provides earlier warning of potential drive issues.
SMART report
A detailed health status overview of a drive, showing reliability metrics and potential warning signs of impending failure.
Snapshot
A point-in-time image of a file system, used by BTRFS and ZFS to enable quick rollbacks, backups, or recovery of previous states.
Spin state
The current rotation status of a hard drive—either spinning (active) or spun down (idle). Managing spin states helps reduce power consumption and drive wear.
Spin-down timers
Settings determining how long a drive remains idle before Unraid spins it down to save power and extend drive life.
Split level
An advanced share setting that controls whether files are split across multiple disks. Affects how Unraid organizes data within a share. Most users can keep the default setting.
SSH
“Secure Shell,” an encrypted protocol for securely accessing and managing your Unraid server remotely through a command-line interface.
SSL
“Secure Sockets Layer,” a security protocol for establishing encrypted connections between your browser and the Unraid webGUI, protecting sensitive information.
See What is SSL?
SSO
“Single Sign-On,” a login method that allows you to use one set of credentials to access multiple services like Unraid Connect.
Standby mode
A low-power state for solid-state drives when they're not actively being used; similar to spinning down a mechanical drive but for SSDs.
Subnet routing
In the context of Unraid, a Tailscale-specific feature that securely connects devices across different networks using encrypted tunnels and subnet routers.
Syslog
The system logging service in Unraid that records system events, errors, and activity for troubleshooting and monitoring.
Syslog server
A centralized server that collects and stores log messages from Unraid, allowing for persistent storage of diagnostic information.
Tailnet
A private, secure network created by Tailscale that connects all your devices running Tailscale, regardless of their physical location. Enables secure remote access to your Unraid server.
Tailscale
A VPN service built on WireGuard that simplifies secure remote access to your Unraid server. Creates an encrypted mesh network between all your devices.
TLD
“Top-Level Domain,” the last segment of a domain name, such as .com or .net. Unraid's default ".local" works for most networks.
TLS
“Transport Layer Security,” the successor to SSL, providing encrypted communication between your browser and the Unraid webGUI for secure administration.
Topology
The structural arrangement of drives in a ZFS pool. Common topologies include mirror, RAIDZ1/2/3, and stripe, each providing different levels of performance and redundancy.
TRIM/Discard
A command that allows the operating system to inform an SSD of which blocks of data are no longer in use, improving the performance and longevity of the drive.
UDMA
“Ultra Direct Memory Access,” a data transfer protocol between the CPU and storage devices. UDMA errors in SMART reports can indicate connection problems with the drive cable or port.
See UDMA - Wikipedia
UEFI
“Unified Extensible Firmware Interface,” a modern replacement for BIOS that provides more features and better security. Required for some VMs and for booting from drives larger than 2TB.
See UEFI - Wikipedia
UPnP
“Universal Plug and Play,” a network protocol that allows devices to discover each other on a network. Used by Unraid to automatically configure port forwarding on compatible routers.
User share
Logical view which combines folders from array drives and pools. Files remain on individual disks; can span zero or more array drives and zero or more pools.
vDisk
A virtual disk file used by a VM as storage. Acts as a virtual hard drive for the guest operating system.
vDisk allocation
The method used to provision storage space for a virtual disk—thin provisioning (allocated as needed) or thick provisioning (allocated at creation).
VFIO
“Virtual Function I/O,” a technology that enables direct assignment of PCIe devices (like graphics cards) to virtual machines, providing near-native performance for GPU-intensive tasks.
Virt
Short for virtualization, referring to Unraid’s capabilities for running virtual machines.
VirtFS
A file-sharing mechanism between the Unraid host and virtual machines, allowing files to be accessed directly from the host system.
See VirtFS | KVM
VirtIO
A set of efficient drivers for virtual machines that improve performance by enabling direct communication between the VM and the host. Recommended for most VM devices.
Virtual disk images
Files that represent physical hard drives in virtual machines. Common formats include qcow2, raw, and vhd.
VM
“Virtual Machine,” a software emulation of a computer that runs its own operating system inside Unraid. Functions as if it were a separate physical computer.
VM XML templates
Preconfigured setups for creating specific types of virtual machines in Unraid. Simplify the process of creating optimized VMs for different operating systems.
VNC session
A remote desktop protocol used to access a virtual machine’s graphical interface directly through the Unraid webGUI.
VPN Tunnel
An encrypted connection between your device and your Unraid server, allowing secure remote access over the internet.
VT-d
“Virtualization Technology for Directed I/O,” Intel’s technology for passing through physical devices to virtual machines. Required for GPU passthrough and other device assignments on Intel platforms.
Wake-on-LAN (WOL)
A network standard that allows a computer to be turned on remotely by sending a special network packet. Used to power on your Unraid server without physical access.
WebGUI
The web-based graphical user interface for managing your Unraid server through a browser. The primary way most users interact with Unraid.
WireGuard
A modern, secure VPN protocol integrated into Unraid that provides encrypted access to your server from the internet. Known for being faster and more straightforward than OpenVPN.
Xen HVM
“Hardware Virtual Machine,” a virtualization mode that uses hardware assistance for full virtualization. Less commonly used in Unraid since the adoption of KVM.
Xen PV
“Paravirtualization,” a legacy virtualization method where the guest OS is modified to work with the hypervisor. Largely superseded by hardware virtualization in modern systems.
Xen virtual disk
A disk format used with Xen virtualization. Most Unraid VMs now use QEMU disk formats instead.
XFS
A high-performance filesystem used as the default for array drives in Unraid. Optimized for large files and good handling of random read/write operations.
ZFS
“Z File System,” an advanced file system and volume manager with built-in features like snapshots, checksumming, and compression. Available for pools in Unraid.
See ZFS - Wikipedia
ZFS ARC
“Adaptive Replacement Cache,” ZFS’s memory-based read cache that intelligently keeps frequently accessed data in RAM. Improves performance but requires adequate memory allocation.
Zpool topologies
The various ways drives can be organized in a ZFS pool, such as mirrors, RAIDZ arrays, or combinations. Determines redundancy, performance, and storage efficiency.