Storage Networking
| Storage networking can be defined as "the hardware and software that enables storage to be consolidated, shared, and accessed over a networked infrastructure."[4] As networks are being used for more functions by more organizations and individuals, the amount of data that is created and must be stored is quickly increasing. This data includes documents, online transaction details, financial information, e-learning courses, corporate videos, and so forth. Before storage networking, data was stored either on embedded disks within servers or on separate disks directly attached to servers, known as directly attached storage (DAS). Neither of these solutions is scalable because they are limited by the capacity of the server. They are also not reliable because access to the data depends on the server being available. Storage networking allows data to be accessed over the network and is therefore not restricted by or dependent on a particular server. Two complementary storage networking models exist:
An NAS device is considered an "appliance" that is installed directly onto a LAN and provides file-oriented access to data. The data stored on these high-performance devices is physically separate from the servers themselves and thus can be accessed by many different protocols. For example, files can be accessed with IP applications (such as Hypertext Transfer Protocol [HTTP] and File Transfer Protocol [FTP]), and the devices can also support file-sharing protocols such as the Network File System (NFS). NAS provides scalability and reliability but can also produce a lot of traffic because data travels between the NAS device, the server, and the client requesting it, all on the LAN. In contrast, a SAN is a dedicated, high-performance network infrastructure that is deployed between servers and disks (called storage resources), as illustrated in Figure 10-2. The disks are interconnected in a separate network that is accessible from the servers. Clients communicate with servers over the LAN (and over a WAN), while servers communicate with disks over the SAN. Figure 10-2. A SAN Is Deployed Between Servers and Disks SAN technology allows a mixture of server platforms and storage devices. Within a SAN, a Fibre Channel infrastructure is typically used. Fibre Channel provides high-speed connectivity over relatively long distances, allowing functions such as backups to be performed quickly on a dedicated network. Because Fibre Channel is not a well-known technology and is expensive to implement, the following two alternative SAN protocols, which use IP, have been developed:
FCIP interconnects SAN islands over an IP network by providing a transparent connection between the Fibre Channel networks. With FCIP, Fibre Channel frames are encapsulated within IP packets, creating a tunnel between two Fibre Channel devices connected to the IP network. The IP network provides the connectivity between the SAN islands, including over a WAN. The IP network uses the Transmission Control Protocol (TCP) to provide reliable delivery. The iSCSI protocol is based on the Small Computer Systems Interface (SCSI) standard that has been around for a long time for communication between PCs and their attached devices, such as printers, disk drives, and so forth. SCSI uses block-oriented access, in which data is formatted into blocks before being sent. SCSI commands, for example, for reading and writing blocks of data, are also used in Fibre Channel technology. The iSCSI protocol enables servers to communicate with Fibre Channel storage over an IP infrastructure by encapsulating the SCSI commands and data into IP packets and using TCP's reliable services. Routers with iSCSI capabilities connect iSCSI devices to Fibre Channel storage. Note Further information on storage and SANs can be found at http://www.cisco.com/go/san and http://www.cisco.com/go/storage, and in the Cisco Press books Storage Networking Fundamentals: An Introduction to Storage Devices, Subsystems, Applications, Management, and File Systems, by Farley, and Storage Area Network Fundamentals, by Gupta. |
EAN: 2147483647
Pages: 156