Understanding Modern Data Storage: From Hard Disks to NAS and SAN

Storage Basics – Hard Disk

In the information age we constantly generate video, music, images, text, and spreadsheets, all of which must be saved on electronic devices—a process known as data storage.

For most users the most common storage device is the hard disk. A computer’s three core hardware components are the CPU (processor), memory (RAM), and hard disk (storage). The CPU performs calculations, the hard disk stores data permanently, and memory acts as a bridge, temporarily holding data for the CPU.

Most desktops, servers, and smartphones use built‑in storage, meaning the hard disk is installed inside the device and connects to the motherboard via dedicated interfaces and data cables.

Typical hard‑disk interfaces are shown below.

Mobile devices use tiny storage chips (eMMC, UFS) soldered directly onto the board.

There are two main types of hard disks: traditional mechanical drives and solid‑state drives (SSD). Mechanical drives consist of one or more rigid metal platters coated with magnetic material; data is read/written by magnetic heads.

The platter surface is divided into concentric tracks, which are further split into sectors (the smallest addressable unit). Older drives used a fixed 512‑byte sector size and CHS (cylinder‑head‑sector) addressing. Modern drives use 4 KB sectors and LBA (Logical Block Addressing). A group of contiguous sectors forms a physical block, making the disk a block device.

What Are Logical Volumes and File Systems?

To simplify management, physical block devices can be partitioned into multiple logical block devices, or several physical devices can be combined into a larger logical device.

Windows provides Disk Management for basic and dynamic disks. Basic disks can be divided into primary, extended, and logical partitions (e.g., the familiar “C:”). Dynamic disks use volumes that can span multiple disks.

Linux uses LVM (Logical Volume Manager). Physical storage is first initialized as Physical Volumes (PV), which are grouped into Volume Groups (VG). From a VG, Logical Volumes (LV) are created.

After creating a logical volume, a file system must be applied. A file system acts like a warehouse manager, organizing data in a hierarchical directory structure. Common file systems include Windows FAT/FAT32/NTFS and Linux ext2/ext3/ext4, XFS, BtrFS, etc. In Windows, formatting a partition assigns a drive letter; in Linux, formatting a logical volume and mounting it makes the storage usable.

What Are DAS, NAS, and SAN?

Beyond internal storage, external storage solutions have emerged to meet growing capacity and maintenance needs.

Direct‑Attached Storage (DAS) connects storage devices directly to a server via dedicated cables (e.g., SCSI). DAS is limited to a single host, making sharing difficult and raising cost and reliability concerns.

Network‑Attached Storage (NAS) and Storage‑Area Networks (SAN) are network‑based solutions. NAS connects multiple hosts over IP networks, providing shared storage with its own file system. However, I/O performance can become a bottleneck as the number of clients grows.

SAN builds on NAS by using dedicated fiber‑channel switches and protocols such as iSCSI or FC, offering higher performance. The key distinction is where the file system resides: NAS includes the file system on the storage device, while SAN presents raw block devices to hosts.

Many households now use small NAS devices that function like mini‑servers, allowing clients to access files via network file systems (CIFS/SMB, NFS) or protocols like FTP and HTTP.