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M. Delfino
communicate freely amongst themselves. Furthermore, the environment is loosely
coupled and is therefore not sensitive to relatively long round-trip time for network
messaging (large network latency). Connected to the network we have the following
elements:
• CPU servers: Elements that receive input data, perform calculations and produce
output data. They do not implement any permanent storage, although they often
provide volatile disk storage used to temporarily store data while executing a
task.
• Disk servers: Elements that store data in a stable and reliable manner with an
access latency (defined as time to open a file and receive the first byte of data)
which is relatively low. They provide inputs to and receive outputs from the CPU
servers. They can also send and receive data to Tape server elements.
• Tape servers: Elements that store data in a stable and reliable manner with an
access latency which is relatively high. They send and receive data to Disk server
elements.
• Information servers: Elements that maintain data in a stable and reliable manner
about the status of the various elements of the distributed computing environment.
• Control servers: Elements that issue commands to trigger operations in other
types of servers and coherently update the relevant Information servers.
• Remote Data servers: Elements that send and receive data from other security
domains, often to Disk server elements via Wide-Area Network (WAN) connections.
The elements of the functional decomposition presented, illustrated in Fig.
14.1, together with the aforementioned powerful network and the maintenance of
coherent security 10 domains, constitute a framework which is sufficient to analyze
the most commonly used distributed computing environments.
The computing industry places a lot of emphasis on how storage is attached to
the computers: Direct-Attached Storage (DAS) does not use a network, attaching
storage hardware via an internal communication bus of a computer; Storage Area
Network (SAN) uses a short-distance network (originally Fiberchannel, with an
increasing tendency towards Ethernet) to couple storage hardware to computers; and
Network Attached Storage (NAS) which uses computers hosting storage devices and
connected to a LAN (or WAN configured to behave like a LAN) to present storage
services to the other computers on the network. These distinctions are important
in environments where few computers are used. In the case of particle physics,
DAS and SAN are used to construct disk servers, which in turn are exposed almost
exclusively in NAS mode.
10 A more precise term is “Authentication and Authorization Infrastructure”, abbreviated as AAI
or AA.
M. Delfino
communicate freely amongst themselves. Furthermore, the environment is loosely
coupled and is therefore not sensitive to relatively long round-trip time for network
messaging (large network latency). Connected to the network we have the following
elements:
• CPU servers: Elements that receive input data, perform calculations and produce
output data. They do not implement any permanent storage, although they often
provide volatile disk storage used to temporarily store data while executing a
task.
• Disk servers: Elements that store data in a stable and reliable manner with an
access latency (defined as time to open a file and receive the first byte of data)
which is relatively low. They provide inputs to and receive outputs from the CPU
servers. They can also send and receive data to Tape server elements.
• Tape servers: Elements that store data in a stable and reliable manner with an
access latency which is relatively high. They send and receive data to Disk server
elements.
• Information servers: Elements that maintain data in a stable and reliable manner
about the status of the various elements of the distributed computing environment.
• Control servers: Elements that issue commands to trigger operations in other
types of servers and coherently update the relevant Information servers.
• Remote Data servers: Elements that send and receive data from other security
domains, often to Disk server elements via Wide-Area Network (WAN) connections.
The elements of the functional decomposition presented, illustrated in Fig.
14.1, together with the aforementioned powerful network and the maintenance of
coherent security 10 domains, constitute a framework which is sufficient to analyze
the most commonly used distributed computing environments.
The computing industry places a lot of emphasis on how storage is attached to
the computers: Direct-Attached Storage (DAS) does not use a network, attaching
storage hardware via an internal communication bus of a computer; Storage Area
Network (SAN) uses a short-distance network (originally Fiberchannel, with an
increasing tendency towards Ethernet) to couple storage hardware to computers; and
Network Attached Storage (NAS) which uses computers hosting storage devices and
connected to a LAN (or WAN configured to behave like a LAN) to present storage
services to the other computers on the network. These distinctions are important
in environments where few computers are used. In the case of particle physics,
DAS and SAN are used to construct disk servers, which in turn are exposed almost
exclusively in NAS mode.
10 A more precise term is “Authentication and Authorization Infrastructure”, abbreviated as AAI
or AA.