In this lesson, you will learn how the physical distance and transmission medium between your CPU and your storage media impact data access speed and latency.
The Direct Attach Pathway
Direct Attach Storage (DAS) refers to drives connected directly to your computer's motherboard via high-speed local buses like SATA, SAS, or NVMe (PCIe). Because the drive is physically wired to the system, the signal travel time—the latency—is measured in nanoseconds. When you execute a read command, the kernel sends a request through the I/O scheduler directly to the controller, which communicates over a high-bandwidth, low-overhead path.
Because DAS is an extension of the local hardware, it is treated as a local block device (e.g., /dev/sda). The latency is predictable and minimal, making it the preferred choice for applications requiring high-concurrency and rapid transaction processing.
The Networked Pathway
Network Attached Storage (NAS) or Storage Area Networks (SAN) operate differently. Your storage is located on a remote server accessible over an Ethernet network. To access this data, the kernel must encapsulate your storage requests into network packets (using protocols like iSCSI or NFS).
When you request a block of data from network storage, the process looks like this:
- The kernel generates an I/O request.
- The network stack wraps this request into packets.
- The packets travel across network switches, which introduce variable delays (jitter).
- The remote device processes the request and sends the data back across the wire.
Even with 10Gbps or faster networking, you are dealing with milliseconds of latency, which is orders of magnitude slower than a local PCIe bus. You can see the mount point of such a device using the mount command, often identified by the protocol prefix:
# Example of a network-attached mount
192.168.1.50:/data/shared /mnt/nas_storage nfs defaults 0 0
While modern network storage is highly scalable and excellent for centralized file sharing, the protocol overhead and the physical limitations of network switches mean that it will never match the raw, low-latency performance of a direct-attached NVMe drive.
Key Takeaway: Direct Attach Storage offers ultra-low latency via local buses, while Network Storage trades higher latency and protocol overhead for centralized data access and scalability.