IT Glossary

My articles regularly use technical terms from Linux, infrastructure, networking and self-hosting. This glossary explains the most important terms briefly, clearly and with a practical focus.

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Airtime

Airtime is the available transmission time on a Wi-Fi channel. All devices share this medium. The decisive factor is not only the amount of data, but how long a device occupies the radio channel. Slow or poorly connected clients consume more airtime and slow down everyone else.

Ballooning

Ballooning is a memory management technique in virtualization. The hypervisor can dynamically shrink or grow the memory assigned to a VM when other virtual machines need RAM. It helps on flexibly used systems, but it is not a replacement for enough RAM headroom under sustained load.

DHCP

DHCP automatically assigns IP addresses and other network settings to devices on a network.

DNS

DNS stands for Domain Name System. It translates names such as kerezovic.de into IP addresses so systems can communicate with each other. DNS is a fundamental service that often stays invisible until it causes problems.

Failover

Failover means that a second system automatically takes over when the first one fails. The goal is to keep services available during disruptions. Common examples include DNS, cluster systems or virtual IPs that switch between two nodes.

HA Cluster

An HA cluster consists of multiple connected systems that run services with high availability. If one node fails, another node can take over so virtual machines or important services continue with minimal interruption.

iSCSI

iSCSI stands for Internet Small Computer Systems Interface. The protocol transports block-level storage over TCP/IP networks and presents remote disks to servers almost as if they were locally attached.

Jitter

Jitter describes variations in latency. The average response time is not the only important metric; how strongly it fluctuates matters as well. High jitter causes sluggish connections, stuttering streams and problems with real-time applications.

LXC

LXC stands for Linux Containers. Multiple isolated systems run lightweight on a shared Linux kernel.

Secure Erase

Secure Erase is an erase command executed directly by the controller of an SSD or NVMe drive. Unlike classic overwriting, it also handles internal storage areas and data distributed by wear leveling.

SAN

A SAN (Storage Area Network) is a dedicated storage network. It provides centralized block storage to servers and is often used in virtualization environments where performance, shared storage and high availability matter.

Snapshot

A snapshot records the state of a filesystem, volume or virtual machine at a specific point in time. It makes it easy to restore older states or run tests with a defined rollback point.

Swappiness

Swappiness is a Linux kernel parameter with values from 0 to 100. It controls how aggressively data is moved from memory into swap storage. A lower value, for example 10, reduces swapping and can improve performance when enough RAM is available.

Unbound

Unbound is a recursive DNS resolver. It can resolve DNS queries itself instead of forwarding them to external resolvers. This improves privacy, control and, in many setups, the traceability of the local DNS infrastructure.

Virtual IP

A virtual IP is an additional IP address that is not permanently bound to one specific system. It can move between multiple hosts and is commonly used for high availability and failover.

Wear Leveling

Wear leveling is a mechanism used by flash storage such as SSDs, USB drives and SD cards. Writes are distributed internally so individual memory cells are not worn out too quickly. This is exactly why secure erasure is more complex on flash storage than on classic hard disks.

ZRAM

ZRAM is compressed RAM that is usually used as fast swap on Linux. Instead of moving data to slow SSDs or SD cards, it keeps the data compressed in memory. This reduces I/O and can make systems noticeably more stable under load.