Storage Basics: Storage Hubs and Switches Page 2
Managed hubs are one step above unmanaged hubs, with the obvious difference being that managed hubs are, well, manageable. Managed hubs are SNMP controllable. As a quick refresher, SNMP is an application layer protocol that enables the exchange of management information between network devices. An SNMP manager resides somewhere on the network and collects management information sent by SNMP agents on the network. Managed hubs are able to be SNMP agents, whereas unmanaged hubs are not.
Some of the common features found with managed hubs include the following:
Hot-Pluggable Ports - Most managed hubs provide a certain number of hot pluggable ports. Like any other hot plug device, these ports allow on-the-fly attachment and detachment of network devices such as servers or storage devices.
Dedicated port speed - When using a managed hub, each of the hub's individual ports can provide 100 Mbps data transfer speeds. The speed of each port on the hub is not affected by the use of the other ports on the hub.
Error Detection - Many managed hubs offer some form of diagnostic capabilities, providing the administrator with a method to see if anything is amiss. Many of the managed hubs are also capable of performing a Power on Self Test (POST). The POST check is run when the hub is powered on and routinely checks the status of internal components and even the status of attached nodes. If a failed node is detected, the port will be excluded from the loop.
Management interface - A managed hub needs an interface, and many of the newer hubs provide easy to navigate graphical interfaces. At the very least, there will always be the traditional command-line interface.
Switched hubs are the most recent addition to the family of Fibre Channel hubs and provide a bridge between the world of hubs and switches. They are manageable and provide the function of a hub in the FC-AL topology, but they also have many of the performance capabilities of a switch. The ports on a switched hub are dedicated, allowing for maximum bandwidth of each port and, unlike a hub, will only direct a data stream to the port that requested that information. Switched hubs also receive a Fibre Channel address and can be involved in protocol activities such as the management of other devices on the network, event logging, and diagnostics.