CompTIA® Server+ Exam Notes : Storage Area Networks, Fiber Channel, Write Through Cache

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21. Two most widely used types of RAM:

  • DRAM - Dynamic RAM, and
  • SRAM - Static RAM. SRAM, being very expensive, commonly used for Cache memory. DRAM, being cheaper, is used for main memory.

22. SIMMs & DIMMs:SIMMs come in both 30 pin (older 386/some 486 compatible) and 72 pin formats. SIMMs must be installed in pairs. On the other hand DIMMs can be installed one at a time. DIMMs usually come in 168 pin configuration.

23. SANs:

  • Advantages of Storage Area Network (SAN):
  • Simplified storage management,
  • Flexibility, and Scalability of architecture
  • Availability, and fast data access.

24. Processors:

  • Windows 95/98 Operating system supports only one micro processor.
  • Windows 2000 Professional supports upto 2 processors.
  • Windows 2000 Server supports a maximum of 4 processors.
  • Windows 2000 Advanced Server supports up to 8 processors.
  • Windows 2000 Data Center Server supports up to 32 processors.
  • Pentium III processor is compatible with Pentium II processor, hardware wise. You only need to upgrade the BIOS on the main board to use improved functionality of Pentium III processor.
  • RISC processors compute simplest instructions in the shortest amount of time possible, as against CISC processors.
  • Pentium Pro was the first CPU package that included the L2 cache inside the CPU package itself.

25. Fiber channel:

  • N_Port stands for Node Port and located at the termination (Node) end.
  • F_Port stands for Fabric Port and is located at the switch end.

Fiber Channel supports three (3) topologies:

  • Point-to-Point:The Point-to-Point connection is the simplest of the three topologies with two N_Ports (such as a Host and RAID system) connected. This topology has limited applications with no expansion capabilities but can serve as a high-speed interface between two points over long distances. The communication is full duplex so a 1 gigabit/sec link delivers 200MB/s of dedicated bandwidth. Point-to-Point configuration costs relatively less due to simplicity of architecture.
  • Arbitrated Loop: Fiber Channel Arbitrated Loop (FC-AL) provides a low cost alternative that allows multiple connections without the aid of a switch. Here, L_Port can be connected to any loop with each port sharing the bandwidth. The connection is half-duplex which means once a port arbitrates and gains access to the loop, transmission of information is in one direction only. This effectively opens a point-to-point connection utilizing 1/2 of the available loop bandwidth.
  • Switched Fabric and Loop: The Fiber Channel Switch is analogous to the Router in networking, managing connections, routing requests to the proper ports, and allowing characteristics to be set on each port. A switch will also automatically configure the port for point-to-point (F_Port) or loop operation (FL_Port).

26. FC-AL supports full-duplex data-transfer rates of 100MBps and is compatible with SCSI.

It is often recommended to lay the fiber for backbone, since it is immune to EMI and also can carry higher bandwidths.

27. Servers using RISC processors are usually designed for high end applications with high availability and larger processing power. Hence, RISC based servers are usually much more expensive than Intel processor based servers.

28. SDRAM is faster compared to DRAM, VRAM, EDORAM.

29. A fail-over describes a mechanism, where if the primary node in a cluster fails, and the secondary node takes over the load of the failed node. During a fail-over, usually the failure (or fail-over) is not noticed by the clients.

30. With Write-Through cache, each write operation to the cache is accompanied by a write operation to the main memory. That means, the data is written to the cache and the main memory at the same time.

With Write-Back cache, the CPU writes to the cache first. But the actual updating of main memory takes place at a later time.

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