360 Systems DigiCart/E - Manual (Page 17)

Installing an Ethernet Audio Network
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Hot Swap
The ability to remove and replace a disk in a drive array while the array is running is called Hot
Swapping. Hot swapping provides higher system availability in the event of a single disk failure. The
failed disk can be replaced and its contents can be reconstructed automatically while the array continues
to function. All RAID levels, except RAID 0, which does not keep redundant data, support hot
swapping.
Special hardware is required to support hot swapping because the process involves removing a disk
from the data bus and power supply. Servers are available with and without this feature. Be certain to
determine your Ethernet Audio system availability and security needs related to this feature.
Ethernet
Typical strategies for increasing the availability of the Ethernet portions of the system, such as wiring
and hubs, is to simply add redundancy. For example, duplicate NICs, cabling and hubs could be routed
independently to separate DigiCarts to provide the required level of system duplication. If one path
failed, the other path would likely be available.
NFS File Server
In order for a computer to be a server on the Ethernet Audio network it must support the NFS file sharing
protocol. Windows 2000 Server software does not include NFS, but an add-in program, Windows Services
for UNIX, is available from Microsoft that provides this feature.
DigiCart/E uses the NFS protocol to communicate with servers. Additional PC or Mac workstations attached
to the network do not need NFS software to communicate with the Ethernet Audio server.
Signal Distribution Equipment
Ethernet is predominately used as a baseband transmission network, where all the network nodes share access
to the network media on an equal basis. Baseband transmission means that data sent over the media uses the
entire bandwidth of the media. Each node has the capability to send data at the Fast Ethernet standard speed
of one-hundred million bits (megabits) per second (100Mbps). Since the nodes are sharing the media, the
actual data speed tends to be significantly less than 100Mbps in much the same way that the speed of a car on
a crowded freeway tends to be significantly less than the posted speed limit. Ethernet is based on a network
access method called Carrier Sense Multiple Access with Collision Detection or CSMA/CD.
On an Ethernet network, all nodes share the network much like an old party line telephone system. Ethernet is
a shared media, so there are rules for sending packets of data to avoid conflicts and protect data integrity.
Nodes determine when the network is available for sending packets. When nodes on an Ethernet network
want to send data to another node, the node first senses (or listens to) the network to ascertain if there are
other contending nodes already sending information. Any node can send information at any time provided
that it first checks to see if the network is already in use. Once the data is sent, the node listens to the network
to see if a collision occurred with data from another node that sent data at some time after the sending node
last listened. If a collision occurs, the node simply re-sends the data until it successfully reaches its destination
address. When there are a relatively small number of nodes on the network, collisions are fairly rare. As the
number of nodes increases (as the number of cars on the freeway increase as in our previous example), the
likelihood of collisions increases proportionately causing increased re-sends and generally decreasing network
performance.
In order to make network performance reliable enough to record or play up to eight 48k digital stereo audio
files concurrently, 360 Systems recommends that network collision domains be limited to eight DigiCart/E
nodes.