Storage Systems - SQL Server 2012 Internals and Troubleshooting - page 84

Choosing the Right Storage Networks
This chapter opened with an example of a SQL Server using a single disk drive. More complex stor-
age networks link multiple hosts, or initiators, to many storage devices, or targets. These advanced
storage area networks facilitate low-latency, high-throughput communication.
The storage network can facilitate the sharing of storage resources. Direct attached storage offers
good performance for a relatively low cost, but DAS storage can orphan performance and capacity.
Imagine several applications that grow in capacity at different rates or are used at different times.
Consolidated storage that is attached to a SAN network enables users to share both storage capacity
and available performance.
Complex storage networks are often built using Fibre Channel (FC) technology.
NOTE The spelling of “Fibre” is no accident. The creators of FC wanted to
differentiate the technology from i ber optic technologies that did not support
copper cabling at the time.
FC differs from most server network protocols in that it is not routed. Routing enables the creation
of large and resilient networks, but routed networks require a lot of overhead to operate.
If you are familiar with Fibre Channel you may already be aware of routing solutions for it. Several
products exist to fuli ll this role; their use is extremely complex and beyond the scope of this
chapter.
Because it is not routed, FC dei nes a standard for both direct and switched storage network connec-
tions. Modern FC networks utilize high-speed network switches to communicate.
Storage networks are not limited to Fibre Channel. Several protocols dei ne methods for sending
storage data over existing server IP networks. Fibre Channel Internet Protocol (FCIP) allows Fibre
Channel data frames to be encapsulated within an IP packet. Internet Small Computer Systems
Interface (iSCSI) allows the transmission of SCSI data over IP networks.
FCIP and iSCSI transport different layers of the storage network. Fibre Channel frames are analo-
gous to Ethernet data frames. SCSI is a storage control system comparable to Internet Protocol.
Transmission Control Protocol is an Internetworking protocol and therefore has no analogue in
storage networking. Emerging technologies such as Fibre Channel Over Ethernet (FCOE) combine
the attributes of existing Fibre Channel networks with Ethernet routed networks.
Regardless of the specii c network technology that is used to transport storage trafi c, keep in mind
that bandwidth is not ini nite. Excessive storage trafi c not only negatively impacts the performance
of a single system, it can hamper all connected components. Many applications must meet minimum
performance requirements spelled out in service-level agreements (SLAs) . Storage network perfor-
mance is critical to overall application performance.