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SCSI: A Standard Interface for Peripheral Devices

Learn about SCSI, a standard interface for connecting peripheral devices to a PC. SCSI can connect up to 16 devices, provides faster data transfer, and is commonly used with devices like CD-ROM drives, scanners, and servers.

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SCSI: A Standard Interface for Peripheral Devices

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  1. Unit 4 SCSI

  2. https://www.youtube.com/watch?v=ggCT4qhZEj0

  3. A small computer systems interface (SCSI) is a standard interface for connecting peripheral devices to a PC. • It can connect up to 16 peripheral devices using a single bus including one host adapter. • SCSI is used to increase performance, deliver faster data transfer transmission and provide larger expansion for devices such as CD-ROM drives, scanners, DVD drives and CD writers. • SCSI is also frequently used with RAID, servers, high-performance PCs and storage area networks • It is either embedded on the motherboard or a host adapter is inserted into an expansion slot on the motherboard. • Each device on a parallel SCSI bus must be assigned a number between 0 and 7 on a narrow bus or 0 and 15 on a wider bus. This number is called an SCSI ID.

  4. https://www.youtube.com/watch?v=zriUU5SuKOw

  5. Terminologies • Chain: Several SCSI devices connected together on the same SCSI bus. • HBA(Host Bus Adapter): Card that acts as an interface between the SCSI bus and a host computer. The HBA is the SCSI card. • SCSI ID: Unique number assigned to each SCSI device on a SCSI bus. Each SCSI device on the bus must have a unique ID, including the SCSI host adapters. • LUN: Provides a way to differentiate between SCSI devices sharing a single SCSI ID. • SCSI bus: Physical path for SCSI data flow. The following are the two general types of SCSI buses: • o Narrow: 8-bit bus, uses 50-pin connector • o Wide: 16-bit bus, uses 68-pin connector • Terminator: Group of resistors placed on the end of a SCSI bus that prevents deflection of SCSI signals. • Target: Another name for a SCSI device.

  6. Difference between SCSI and LUN • The easiest way to differentiate between these two terms is to consider how houses are arranged on a street. Each house has a unique address, or number, assigned to it. • The same can be said about SCSI devices on a SCSI bus. Now picture an apartment building containing several apartments. • With one building and a single street address, another method is needed to differentiate each apartment. Therefore, each apartment gets its own apartment number. • Think of LUNs as the equivalent to apartment numbers. Sometimes several SCSI devices will share a SCSI ID.

  7. A LUN refers to a "logical unit number" presented to a host as a SCSI ID. (i.e., LUN number 1 specifies SCSI ID 1 on that port. Therefore, the term volume can be considered software based and LUN considered hardware based.

  8. SCSI Bus Types • To keep it simple, a SCSI bus is the data path between SCSI devices. The bus consists of the HBA, cables, and terminators that make up the connections between all SCSI devices. • When several devices are connected on a single SCSI bus, they're typically referred to as being daisy chained. Narrow SCSI uses an 8-bit bus, with 0 to 7 being the valid range of IDs. • Wide SCSI typically uses a 16-bit bus, with 0 to 15 being the range of possible SCSI IDs.

  9. Different Categories of SCSI Parallel Interface • The predominate SCSI interface today is the parallel interface, which is divided into the following categories: • 1. Single-ended (SE) • 2. Differential, or high voltage differential (HVD) • 3. Low voltage differential (LVD)

  10. Single Ended • Used for signaling using interface and buses within the PC. • Conventional logic is used: a positive voltage is a "one", and a zero voltage (ground) is a "zero“. This is calledsingle-endedsignaling. • Differential SCSI is a great idea in theory, and one might have thought it would become very popular. In fact, this never happened in the PC world, largely due to cost. The circuits needed to drive differential signals are more expensive and use more power than those for single-ended SCSI. For many years, single-ended SCSI was "good enough", and allowed cable lengths sufficient for the needs of most users, so little impetus was seen to move to the more expensive differential signaling.

  11. Icons for hardware using single-ended SCSI (left)and regular (high voltage) differential SCSI (right).

  12. High voltage differential (HVD) signaling uses two wires for each signal to improve signal integrity and allow long cables to be used without data loss or corruption. • expensive to implement • uses a great deal of power. • Instead, a third option was created, with the intention of marrying the best attributes of both SE and HVD signaling. This is a differential signaling method that was designed to use the advantages of differential signaling to allow long cable lengths, while reducing implementation cost and allowing for electrical compatibility with single-ended devices. This technology is called low voltage differential or LVD signaling.

  13. Many single-ended and LVD devices are compatible with each other, and you'll often see the distinction "LVD/SE" on many SCSI HBAs, alerting you that the adapter supports both interfaces. You can't mix LVD and HVD or single-ended and HVD on the same SCSI bus, unless your intention is to set your SCSI devices on fire! • A problem with single-ended devices is electrical noise. In areas of high electromagnetic radiation, SE SCSI can have problems.

  14. Why is SCSI required to be properly terminated? Where should it be terminated? • Terminators prevent a SCSI signal from being reflected up and down the SCSI bus repeatedly. Terminators act as a load that a SCSI signal can be dissipated across, thus absorbing the signal and clearing the SCSI bus. Without the right terminators, your SCSI bus won't work properly. • You must place your terminators in the right locations on the SCSI bus. The simple rule of thumb regarding termination is to place a terminator at the end of the bus. Be careful not to use a terminator in the middle of a bus.

  15. Fibre Channel • https://www.youtube.com/watch?v=KDcdgcRtvBQ

  16. Fibre Channel • Fibre Channel is a high-speed networking technology primarily used for transmitting data among data centers, computer servers, switches and storage at data rates of up to 128 Gbps. • It was developed to overcome the shortcomings of the Small Computer System Interface (SCSI) and High-Performance Parallel Interface (HIPPI) by filling the need for a reliable and scalable high-throughput and low-latency protocol and interface. • FibreChannel is especially suited for connecting servers to shared storage devices and interconnecting storage controllers and drives. The Fibre Channel interface was created for storage area networks (SANs).

  17. advantages and disadvantages offered by the Fiber channel architecture • Fibre Channel architecture is versatile and scalable, offering the following advantages: • 1. Faster than SCSI, offering up to 4Gb/sec (500MB/sec) data transfer rates • 2. Allows cables distances to be as long as 10 kilometers • 3. Supports up to 16 million interconnected storage devices • 4. Allows for real-time hotswapping, permitting you to add and remove devices from a live bus, without any service interruption • 5. Gives you the ability to configure a SAN, which allows you to consolidate all your essential storage, including backup libraries, on a backend network

  18. Disdavantages • It's more expensive than SCSI. • Implementations are more complex. • It requires additional maintenance considerations.

  19. Different types of fiber channel cables • You can implement Fibre Channel using either copper cable or fiber-optic cable. Copper is much less expensive to implement and maintain than fiber-optic cable, but it doesn't offer the same potential bandwidth (currently 2Gb/sec maximum compared to 4Gb/sec with fiber optic). • You can connect copper cable in a Fibre Channel network using either an intracabinet configuration or an intercabinet configuration. The differences between the two are as follows: • 1. Intracabinet: The maximum cable length is 13 meters, and all connections are typically made within a single enclosure. • 2. Intercabinet: The maximum cable length is 30 meters, and all connections are typically made between several enclosures.

  20. Fiber-optic cables are generally referenced by their mode, or frequency, that the cables support. The following are the two fiber-optic modes: • 1. Single-mode (9 micron): Fiber-optic cable that allows for a maximum distance of 10 kilometers and offers a bandwidth of 4Gbps with plans for expansion to 10Gbps • 2. Multimode: Multimode cables come in two forms: • o 62.5 micron: Offers a maximum distance of 175 meters • o 50 micron: Offers a maximum distance of 500 meters • the smaller the micron, the greater the distance the cable can support. The term micron refers to the size of the core of the optical cable.

  21. Different devices used in fiber channel SAN • Among the hardware devices that you'll use in a Fibre Channel SAN are the following: • 1. HBA • 2. Gigabit Interface Converter (GBIC) • 3. Switch • 4. Hub • 5. Bridge/router

  22. Host Bus Adapter • Fibre Channel HBAs providing an interface between a server's internal PCI bus and a Fibre Channel network. • To connect a server to a Fibre Channel network, you need to connect the HBA to a Fibre Channel cable. This is similar to using SCSI via an HBA on any PC or server.

  23. Gigabit Interface Converter (GBIC) • GBICs are modular transceivers that allow you to interconnect Fibre Channel cable to Fibre Channel devices such as switches and routers. • The job of the GBIC is to convert the Fibre Channel signal from the transmission medium to data that can be interpreted by the HBA or switch.

  24. Switch • Fibre Channel switches usually connect devices on the Fibre Channel network. • In terms of connecting to the SAN, some switches have ports designed to connect to GBICs, while other switches allow Fibre Channel cable to be plugged directly into them. • The types of ports that a switch supports will tell you the type of networks to which the switch can connect. These are the most popular switch port types: • 1. F_Port: Used for switched-fabric topologies • 2. FL_Port: Used for Fibre Channel-arbitrated loop (FC-AL) topologies • 3. U_Port: Used for universal port (fabric or FC-AL) • 4. E_Port: Used to interconnect Fibre Channel switches

  25. Hubs • Like with Ethernet hubs, bandwidth in a Fibre Channel hub is shared, meaning that only one host connected to the hub can transmit data at a time. • Although less expensive than switches, their inefficient bandwidth utilization make them a less desirable choice.

  26. Bridge/Router • The bridge, or router, is a device that's used to connect a Fibre Channel SAN to a SCSI device. The job of the device is to bridge Fibre Channel communications to SCSI bus communications; hence, it has the name bridge. • For whatever reason, however, no vendor seems to want to go out on a limb and call this device what it'd be called in the world of Ethernet—a brouter (bridging router)!

  27. different fiber channel network topologies. • Fibre Channel networks are connected using one of three different topologies: • 1. Point-to-point topology • 2. Switched-fabric topology • 3. Arbitrated-loop topology

  28. Point to point topology • This is equivalent to using a crossover cable to interconnect two computers on a network without needing a hub or switch.

  29. Switch fabric topology • Switched fabric has emerged as the most popular Fibre Channel topology. The simplest way to think of switched fabric is as an equivalent to Ethernet networking. • Each device connected to the SAN will connect to a port on a switch. For scalability, you can add purposed switches to the SAN fabric.

  30. Arbitrary loop topology • Arbitrated loop is the equivalent to a Token Ring network topology. Arbitrated-loop topologies support up to 127 nodes interconnected through a hub. • Although this topology is less expensive to implement because of the lesser cost of Fibre Channel hubs over switches, it's also not as scalable or efficient.

  31. different methods to connect fiber channel switches and router • Most of your switches and routers allow you to connect and configure them using up to three methods: • 1. Telnet • 2. Hyperterminal • 3. HTTP (Web browser) • From there you can configure the TCP/IP settings of the device so it can be accessed with either Telnet or HTTP. You'll probably find the HTTP interface to be the easiest to use.

  32. Zoning • If all your servers are connected to the SAN, and nearly all server storage resides on the SAN, then you have a potential security nightmare. Imagine the server in the engineering department being able to see all the storage on the finance server. • Also, if two systems attempt to write to the same physical disk at the same time, the disk can become corrupt. You can avoid these problems with zoning. • The easiest way to think of zoning is of the SAN equivalent to VLANs. With LANs, you can set up VLANs on a switch to segment the single physical switch into multiple logical switches.

  33. FCP, FCIP,iFCP • FCP is the Fibre Channel Protocol, which is really another name for running SCSI commands over Fibre Channel. Storage for open systems uses SCSI commands in most cases. • FCIP (FC over IP) is taking the Fibre Channel packets containing the SCSI commands and sending them over Ethernet using IP. • iFCPconverts FC packet address to use IP addresses, and then sends the FC packet over IP and Ethernet. It then converts it back to FC with a different address based on a name server. The management of FCIP is usually done by the storage administrator, while the management of iFCP is usually done by a network guy.

  34. iSCSI(Internet Small Computer Systems Interface) architecture • iSCSI architecture involves a host configured as an iSCSI target. The iSCSI target can be a server with locally connected storage (IDE, SCSI, or even Fibre Channel) or can be a storage device that natively supports iSCSI. Clients that access the storage over the network using the iSCSI protocol are known as initiators.

  35. iSCSI supports both encrypting authentication and encrypting the data payload. iSCSI supports the following methods for the iSCSI target to authenticate iSCSI initiators: • 1. Challenge Handshake Authentication Protocol (CHAP) • 2. Kerberos version 5 • 3. Simple Public Key Generic Security Service (SPKM1) • 4. Simple Public Key Generic Security Service version 2 (SPKM2) • 5. Secure Remote Password (SRP)

  36. SAN backup types • Performing LAN free backups • If servers are directly connected to the SAN and are backing up to storage devices located in the SAN, then by definition those servers are performing LAN-free backups. When backup data doesn't traverse the LAN, it's considered LAN-free

  37. Performing Server free backups

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