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+# Linux – Storage
+
+Overview of storage concepts on Linux systems. It Focus on how disks, partitions, file systems, and mount points fit together.
+
+General introduction to Linux and its filesystem layout:
+
+- [Linux / Basics](./Basics.md)
+
+---
+
+## 1. Disks, Partitions, and Devices
+
+On Linux, disks and partitions are exposed as device files under `/dev`.
+
+Typical examples:
+
+- `/dev/sda`, `/dev/sdb` – whole disks (SATA/SCSI).
+- `/dev/nvme0n1` – NVMe disk.
+- `/dev/sda1`, `/dev/sda2` – partitions on `/dev/sda`.
+- `/dev/nvme0n1p1` – partition on an NVMe disk.
+
+Key ideas:
+
+- A **disk** can contain one or more **partitions**.
+- A **file system** is created on a partition (or on other block devices such as LVM volumes).
+
+---
+
+## 2. File Systems
+
+Common Linux file systems include:
+
+- **ext4** – widely used default file system on many distributions.
+- **xfs** – often used on servers, good for large files and parallel workloads.
+- **btrfs**, **zfs** – advanced file systems with snapshots and additional features.
+
+Responsibilities of a file system:
+
+- Organising data into files and directories.
+- Tracking metadata (permissions, timestamps, ownership).
+- Handling allocation on the underlying block device.
+
+The choice of file system depends on requirements such as performance, robustness, and feature set (for example snapshot support).
+
+---
+
+## 3. Mount Points and the Unified Tree
+
+Linux presents storage through a single unified directory tree.
+
+To make a file system available, it is **mounted** at a directory path (the mount point).
+
+Examples:
+
+- A root file system on `/`.
+- Additional storage mounted under `/srv`, `/mnt`, or `/data`.
+- Removable media mounted under `/media` or `/run/media`.
+
+Important aspects:
+
+- The same directory path can hide existing contents when a new file system is mounted on top of it.
+- Consistent mount points simplify backups and documentation.
+
+---
+
+## 4. /etc/fstab and Persistent Mounts
+
+The file `/etc/fstab` defines which file systems are mounted at boot.
+
+Each entry typically specifies:
+
+- The device (for example a UUID or `/dev/sda1`).
+- The mount point (for example `/srv/data`).
+- The file system type (for example `ext4`).
+- Mount options.
+
+Conceptual points:
+
+- Using UUIDs or labels makes mounts more stable than relying on `/dev/sdX` names.
+- Mount options can influence performance and safety (for example `noatime`, `defaults`, `ro`).
+- Misconfigured entries can prevent the system from booting cleanly, so changes should be tested carefully.
+
+Project‑specific mount layouts (for example for application data) can be documented alongside the systems that use them.
+
+---
+
+## 5. LVM and RAID (Overview)
+
+In addition to simple disk‑partition‑filesystem setups, Linux supports more advanced storage layers.
+
+### 5.1 LVM (Logical Volume Manager)
+
+LVM introduces an extra abstraction layer:
+
+- Physical volumes (PVs) are typically partitions or whole disks.
+- Volume groups (VGs) combine one or more PVs.
+- Logical volumes (LVs) are created inside VGs and used like regular block devices.
+
+Advantages:
+
+- Flexible resizing of logical volumes.
+- Ability to span volumes across multiple physical disks.
+
+### 5.2 RAID (mdadm and hardware RAID)
+
+RAID (Redundant Array of Independent Disks) is used for redundancy, performance, or both.
+
+Common levels:
+
+- RAID 1 – mirroring for redundancy.
+- RAID 5/6 – striping with parity.
+- RAID 10 – combination of striping and mirroring.
+
+Implementation options:
+
+- Software RAID with `md` devices (managed by tools such as `mdadm`).
+- Hardware RAID controllers that present a single virtual disk.
+
+LVM and RAID are often combined for flexibility and resilience.
+
+---
+
+## 6. Swap Space
+
+Swap provides additional virtual memory by using disk space when physical RAM is exhausted.
+
+Swap can be configured as:
+
+- A dedicated swap partition.
+- A swap file on an existing file system.
+
+Considerations:
+
+- Swap is much slower than RAM, but can prevent out‑of‑memory conditions.
+- On some systems, hibernation relies on swap configuration.
+
+---
+
+## 7. Monitoring Space Usage (Conceptual)
+
+Administrators need to keep track of available disk space and inode usage.
+
+Key concepts:
+
+- Total vs used vs available space for each mounted file system.
+- Inode counts (maximum number of files/directories a file system can track).
+- Distinguishing usage on the root file system from usage on separate data file systems.
+
+Concrete commands for checking disk and inode usage can be listed in:
+
+- [Linux / Cheat Sheet](./CheatSheet.md)
+
+---
+
+## 8. Backup‑Friendly Layouts
+
+Storage layout has a strong impact on backup and restore strategies.
+
+General considerations:
+
+- Separating system files from application and user data simplifies targeted backups.
+- Grouping related data under well‑defined mount points (for example `/srv`) makes it easier to snapshot or back up.
+- Avoiding unnecessary writes on system partitions can reduce wear on SSDs.
+
+Backup strategies themselves are usually documented alongside the systems or applications that depend on them.
+
+---
+
+## 9. Relation to Other Documents
+
+- High‑level Linux concepts: [Linux / Basics](./Basics.md)
+- Administration topics (permissions, services, backups): [Linux / Administration](./Administration.md)