Basic storage abstractions on Linux

Published: Thu Apr 20 2023

Topics: linux

Some of the first concepts you come in contact with when installing and using a GNU/Linux distribution for the first time are those related to storage. I would have saved a lot of time in my projects with linux if I had studied the fundamentals of storage sooner.

The following is a condensed and simplified summary of five concepts that you will need in order to better understand Linux (and most other OS’s). Hence, this will be useful for working with personal computers, bare metal servers, virtual machines, docker containers, IoT devices, etc.

Here is a list, ranging from the most concrete to the most abstract:

Drive: Physical storage medium or device
Disk: OS representation of a drive
Partition: Contiguous part of a disk
Volume: Formatted partition
Image: Snapshot of disk, partition or volume

Let’s elaborate on each one.

Drive

A physical device that has the capability of storing raw (digital) data. It is the physical substrate that contains the immaterial data. The more correct name for it would be storage medium or device.

Sometimes it is used informally to refer to any of the other categories 🤦‍♂️️

There are two main types, with respect to the storage technology:

HDD: Hard Disk Drives. It uses magnetic storage on a spinning metal disk.
SSD: Solid State Drives. It uses flash memory, that is, chips (silicon transistors aka MOSFETs) to store bits.

Disk

It is the representation of the Drive within an operating system, like Linux.

The OS assigns a name to each disk.

On Linux, the most common names are:

sdx for SSD drives, where x is an integer beginning from 1
hdx for HDD drives, where x is an integer beginning from 1

Example: A computer with two SSDs and one HDD will have disks named as follows: sda, sdb and hda

On Windows, all regular hardware disks have the ‘disk’ prefix and an integer beginning from 0

Example: A computer with two SSDs and one HDD will have disks named as follows: disk0, disk1, disk2

A disk has a special sector or place for the partition table: a data structure that defines how the disk is divided into one or more partitions.

The partition configuration of a disk can be implemented with any of several existing partition schemes. The most popular are:

MBR: Master Boot Record. MBR can only handle four primary partitions and 2TB of HDD space GPT: GUID Partition Table. GPT has no partition limit.