Storage Systems - SQL Server 2012 Internals and Troubleshooting - page 79

server, it is called Direct Attached Storage (DAS). A storage device managed by a dedicated external
array controller is called Storage Area Network (SAN) attached storage. Figure 4-1 shows the basic
building blocks of a storage subsystem.

CPU

CPU Cache

Disk

Server RAM Memory

Disk

Storage
Array

Disk

Fibre Channel
Switch

HBA 1

Fibre Channel
Switch

Disk

HBA 2

Physical SQL Server

FIGURE 4-1

Storage devices connected to a storage network that are not logically grouped are called, rather inel-
egantly, a JBOD, for “just a bunch of disks (or drives).” Figure 4-2 shows an example of a JBOD.
JBODs can be accessed directly by SQL Server as individual physical disk drives. Just remember
that JBODs do not offer any protection against failure.

Disk Drive Disk Drive Disk Drive Disk Drive

FIGURE 4-2

Storage array controllers group disks into volumes called a redundant array of inexpensive disks
(RAID). RAID-constructed volumes offer capacity without failure protection. The simplest type of
unprotected RAID set is often called disk striping , or RAID 0.