Understanding Storage Basics and FC‑SAN: Comparison of DAS, NAS, and SAN

Storage refers to the practice of saving data on appropriate media in a safe, efficient manner so that it can be accessed when needed. It encompasses both the physical media where data resides (temporary or long‑term) and the methods or processes that ensure data integrity and security.

Storage Area Network (SAN) creates a networked storage environment. SAN’s networking aligns with the trend of server architecture networking. FC‑SAN relies on Fibre Channel (FC) technology, which supports protocols such as HIPPI, IPI, SCSI, IP, and ATM, separating communication protocols from the physical transport medium, allowing multiple protocols to share a single physical link. SAN can also be deployed over IP (IP‑SAN).

The hardware foundation of FC‑SAN consists of three parts:

Storage and backup devices, including tape libraries, disk arrays, and optical libraries.

Fibre Channel network components, such as host bus adapters, drivers, optical cables, hubs, switches, and bridges between Fibre Channel and SCSI.

Application and management software, including backup software, storage resource management tools, and device management utilities.

Advantages of FC‑SAN

(1) Easy network deployment.

(2) High‑speed storage performance – because SAN uses Fibre Channel, it offers higher bandwidth (up to 1062.5 Mb/s) and full‑duplex serial communication.

(3) Strong scalability – the networked architecture allows easy expansion, with Fibre Channel supporting up to 10 km links, enabling physically separated storage locations.

DAS, NAS, and SAN Comparison

1. Connection Method

DAS connects storage devices directly to application servers, offering flexibility but limited scalability. NAS uses network protocols (TCP/IP, ATM, FDDI) to connect storage, providing flexible placement and higher speeds with modern 10 GbE. FC‑SAN employs Fibre Channel to link storage and servers, delivering superior throughput and scalability. All three coexist and together account for over 70 % of the disk storage market, though SAN and NAS are generally more expensive than DAS.

Modern SAN/NAS systems can use thin provisioning to mitigate earlier allocation inefficiencies, yet they still face challenges. SAN is typically used for large‑scale network storage and is expected to grow with hybrid storage technologies.

2. Application Scenarios

DAS is suitable for small‑to‑medium enterprises with modest data volumes and high I/O performance requirements.

NAS is ideal for file servers handling unstructured data, offering flexible deployment and lower cost despite Ethernet speed limits.

SAN fits large applications or database systems, though it comes with higher cost and complexity.

Below are the original illustration images from the source (retained for reference):

Additional images omitted for brevity

For further reading, the original article provides download links to related white‑papers and e‑books on storage technologies, data‑center networking, and distributed storage architectures.