Storage Provisioning and Networking - Deploying and Managing a Cloud Infrastructure - page 250

environment. If applications and services are running in the cloud, then data sources should
be placed near those applications and services. This essentially translates to cloud-based
storage, which eliminates unnecessary problems with the overall system infrastructure.

Cloud vs. SAN Storage

The primary purpose of SANs is to make storage devices, typically disk arrays, accessible to
servers throughout the network such that these devices appear as if they are locally attached
to the operating system. A SAN does not provide file abstraction, only block-level opera-
tions. However, file systems that are built on top of a SAN do provide file-level access and
are called SAN file systems (Figure 9.3).

FIGURE 9.3 How a SAN works

Web Unix Win

Server LAN

WAN

LAN

Application
server

DB
server

Mail
server

Optical/HDD

RAID

This scheme comes with some particular benefits. Because the SAN disks appear as
local devices, servers can boot directly from SAN storage. This allows quick replacement of
faulty servers and fast reconfiguration of the replacement server to acquire the logical unit