The Basics: How Nas Works; File Serving Component; Hardware Component; Storing Component - Aberdeen AberNAS 120 Manual

The Basics: How NAS Works

This section provides a brief introduction to how the NAS server works, and is included to help
provide the context for many of the NAS features available with Windows Storage Server 2003. Like
all NAS servers, Windows Storage Server 2003 functionally and architecturally consists of three
components: the filing system, the wiring (and related hardware), and the storage (disk
components together provide the functionality necessary to fulfill client system application requests
for data stored on the NAS device.
Application requests to read or write data are initiated by the client system, and can be directed to the
storage local to the client (embedded or directly attached storage), or can be redirected over the
network to the NAS device using network transport protocols. These I/O requests are then processed
by the NAS operating system before being passed to the disk devices for storage.

File Serving Component

The process of storing and retrieving the data requested by user applications is known as file serving.
File serving is under control of the operating system software.
1. Application I/O requests (to read or write data) flow from client-side applications over the LAN to
the NAS operating system (kernel), which queues and schedules the various client application
requests. These requests then pass to the file system and the volume manager of the operating
system.
2. The file system portion of the operating system controls security and determines whether or not a
file can be created, opened, written to. The file system also ensures that the file is addressed to
the correct storage destination. The I/O request then passes from the file system through the
Volume Shadow Copy Service layer (where it may or may not be processed) to the volume
manager.
3. The volume manager portion of the operating system readies the data for the specific device(s) it
will be passed onto for storage
component of the volume manager (but not a component of I/O requests).

Hardware Component

Having passed out of the operating system, the I/O request travels over the host bus to the host I/O
controller, which is responsible for correctly addressing the appropriate storage device and correctly
transferring the I/O request commands and data across the storage I/O bus to the storage device.

Storing Component

Having passed into the storage device, the application request (data) is stored on the appropriate
physical or logical disk, as directed by the file system.
3
Disks can be both physical and logical (virtual).
4
It is at this step that the data associated with the application request is converted from file format into the constituent
granular blocks that are written to storage devices.
4
. The Virtual Disk Service (see later section in this paper) is a
Microsoft® Windows Storage Server 2003 White Paper
3
). These