BECAS ESTUDIANTILES PARA LAS UNIVERSIDADES ESTATALES (BEUNE) PLAN DE TRABAJO
7. VINCULACIÓN DEL PROYECTO CON PLANES 2011-2015 a Vinculación con los objetivos y acciones estratégicas del PLANES 2011-
A Fibre Channel SAN employs a fabric to connect devices, or end points. A fabric can be as simple as a single cable connecting two devices, akin to server attached storage. However, the term is most often used to describe a more complex network to connect servers and storage utilizing switches, directors, and gateways.
Independent from the size of the fabric, a good SAN environment starts with good planning, and always includes an up-to-date map of the SAN.
Some of the items to consider are:
How many ports do I need now?
How fast will I grow in two years?
Chapter 6. Fibre Channel products and technology 111
Do I need long distance solutions?
Do I need redundancy for every server or storage?
How high are my availability needs and expectations?
Will I connect multiple platforms to the same fabric? We show a high-level view of a fabric in Figure 6-1.
Figure 6-1 High-level view of a fabric
6.2.1 Bridges and gateways
A bridge is a device that converts signals and data from one form to another. In the specific case of SAN, a bridge is a unit converting between Fibre Channel and legacy (or existing) storage protocols such as:
SCSI
SSA
The offerings from IBM are called SAN Data Gateways or SAN Data Gateway Routers. Depending on the particular bridge, it may be possible to have only a single Fibre Channel port, whereas some will support multiple ports.
ESS Tape JBOD ESS Switch Director
6.2.2 Arbitrated loop hubs
FC-AL topology allows devices be connected using discreet cabling, or an Arbitrated Loop hub.
In FC-AL all devices on the loop share the bandwidth. The total number of devices that may participate in the loop is 126, without using any hubs or fabric. For practical reasons, however, the number tends to be limited to no more than 10 and 15.
Hubs are typically used in a SAN to attach devices or servers that do not support switched fabric only FC-AL. They may be unmanaged hubs, managed hubs, or switched hubs.
Unmanaged hubs serve as cable concentrators and as a means to configure the Arbitrated Loop based on the connections it detects. When any of the hub’s interfaces, usually GBIC, senses no cable connected, that interface shuts down and the hub port is bypassed as part of the Arbitrated Loop configuration. Managed hubs offer all the benefits of unmanaged hubs, but in addition offer the ability to manage them remotely, using SNMP.
6.2.3 Switched hubs
Switched hubs allow devices to be connected in its own Arbitrated Loop. These loops are then internally connected by a switched fabric.
A switched hub is useful to connect several FC-AL devices together, but to allow them to communicate at full Fibre Channel bandwidth rather than them all sharing the bandwidth.
Switched hubs are usually managed hubs.
6.2.4 Switches and directors
Switches and directors allow Fibre Channel devices to be connected (cascaded) together, implementing a switched fabric topology between them. The switch intelligently routes frames from the initiator to responder and operates at full Fibre Channel bandwidth.
Note: In its early days, FC-AL was described as “SCSI on steroids”. Although FC-AL has the bandwidth advantage over SCSI, it does not come anywhere close to the speeds that can be achieved and sustained on a per port basis in a switched fabric. For this reason, FC-AL implementations are, by some observers, considered as legacy SANs.
Chapter 6. Fibre Channel products and technology 113 It is possible to connect switches together in cascades and meshes using inter-switch links (E_Ports). It should be noted that devices from different manufacturers may not interoperate fully.
The switch also provides a variety of fabric services and features such as:
Name service
Fabric control
Time service
Automatic discovery and registration of host and storage devices
Rerouting of frames, if possible, in the event of a port problem
Storage services (virtualization, replication, extended distances)
It is common to refer to switches as either core switches or edge switches depending on where they are located in the SAN. If the switch forms, or is part of the SAN backbone, then it is the core switch. If it is mainly used to connect to hosts or storage then it is called an edge switch. Like it or not, directors are also sometimes referred to as switches. Whether this is appropriate or not is a matter for debate outside of this book.
6.2.5 Multiprotocol routing
Beginning to make an impact on the market are devices that are multiprotocol routers and devices. These provide improved scalability, security, and
manageability by enabling devices in separate SAN fabrics to communicate
without
merging fabrics into a single, large SAN fabric. Depending on the manufacturer, they support a number of protocols and have their own features, such as zoning. As their name suggests, the protocols supported include: FCP FCIP iFCP iSCSI IP
6.2.6 Service modules
Increasingly, with the demand for the intermix of protocols and the introduction to the marketplace of new technologies, SAN vendors are starting to adopt a modular system approach to their components. What this means is that service modules can be plugged into a slot on the switch or director to provide functions and features such as virtualization, the combining of protocols, storage services, and so on.
6.2.7 Multiplexers
Multiplexing is the process of simultaneously transmitting multiple signals over the same physical connection. There are two common types of multiplexing used for fiber optic connections based on either time or wavelength:
Time Division Multiplexing (TDM)
Wavelength Division Multiplexing (WDM)
Dense Wavelength Division Multiplexing (DWDM)
6.2.8 Storage considered as legacy
In the context of a SAN, legacy (or existing) equipment consists of devices that do not inherently support Fibre Channel. As an example, SCSI disk arrays, tape drives, and SSA devices may be considered as legacy (or existing) equipment. In order to protect your investment, it is often a requirement that legacy (or existing) equipment gets reused after the implementation of SAN.
A bridge, router, or gateway device is used to convert between these protocols. These have Fibre Channel connectivity offering connections to the legacy (or existing) equipment at the same time.