What is the difference between a switch and a hub? When should one be used over the other?
A switch provides a "fabric" whereas a hub provides a loop. Bandwidth in a switch is not shared as it is in a hub. Switches are more expensive than hubs but their price is dropping. To me, the only reason that someone would use a hub would be if they are severely cash strapped or want an entry-level Fibre Channel solution. Hubs can be connected to switches though what is known as an FL port. –
There are many difference between a switch and a hub:
HUB - All port on a hub share 100MB/s bandwidth,
SWITCH - Each port of a fabric switch has 100MB/s bandwidth dedicated.
(200 MBps full duplex for 1GB switches)
2) Fibre Channel Address:
HUB - Hubs adopt loop topology, all devices connected to a hub form a single
loop and use AL_PA address (1 byte) to communicate with each other. (There are 127 AL_PA address defined by Fibre Channel standard. -
So you cannot build a SAN with more than 127 nodes by only cascading hubs.)
SWITCH - Fabric switches use 3-byte fibre channel address, and one “San” can
be up to 239 switches. There are 1.5 million address, so Fabric switches is suitable to build large SAN.
3) SNS: (Simple Name Service)
HUB – does not provide SNS –this caused a server to probe all 127 AL_PA to
find storage device.
WITCH – does provide SNS –this allow a server to find the storage device by
lookup the SNS table.
HUB – In a hub environment, when a device is power-on, it will initial a LIP to
negotiate a AL_PA address. During a LIP all communications with-in the
hub environment are suspended.
SWITCH – In a fabric environment, when a device is power-on. The device only
communicates with the fabric-port it connected and does not suspend the
communications of the devices which attached to other ports.
5) Price: Fabric switches are more expensive than hubs..
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