SCSI Device Cables - CompTIA A+ 220-1101 - 3.1

Summary

This script delves into the Small Computer Systems Interface (SCSI), a versatile standard for connecting storage devices, scanners, printers, and more. It highlights the evolution from parallel to serial communication with iSCSI and SAS, the ability to daisy chain up to 16 devices, and the intelligent identification of devices within a chain. The video also touches on the physical aspects of SCSI, including connectors, terminators, and the transition from PATA to SATA, showcasing the enduring relevance of SCSI in modern virtual systems.

Takeaways

• 📚 SCSI stands for Small Computer Systems Interface, a standard interface for connecting various devices like storage, scanners, and printers.
• 🔗 SCSI allows for daisy-chaining multiple devices, supporting up to 16 devices in a single chain, enhancing connectivity efficiency.
• 🌐 iSCSI, or SCSI over IP, is a newer standard that enables SCSI implementation in virtual networks, adapting to modern connectivity needs.
• 🔌 SCSI supports both parallel and serial connectivity, offering flexibility in how devices can be connected depending on the format used.
• 📦 Before SATA and USB, SCSI was the primary method for connecting peripherals like scanners and CD-ROM drives, highlighting its historical significance.
• 💡 SCSI is intelligent, automatically identifying devices in a chain and facilitating access without manual configuration by the user.
• 🔍 Despite its decline in popularity, SCSI is still used in certain systems, especially in virtual environments, showing its enduring utility.
• 🔩 The script describes a SCSI Ultra 3 interface with a 68-pin connector, illustrating the physical aspects of SCSI connectivity.
• 🆔 SCSI uses unique ID numbers for each device in a chain to differentiate and manage multiple devices connected to the same interface.
• 🛑 SCSI terminators are used at the end of a cable to ensure proper communication across all devices in a chain, a crucial aspect of SCSI setup.
• 🔄 Serial Attached SCSI (SAS) is a recent standard that simplifies SCSI configuration by eliminating the need for manual ID setting and terminators.
• 🔄 The transition from parallel to serial communication in SCSI, as seen in SAS, has increased throughput and simplified implementation, aligning with modern technological advancements.

Q & A

What is the acronym SCSI stand for?

SCSI stands for Small Computer Systems Interface, which is a standard interface used to connect various devices like storage devices, scanners, printers, etc., to a computer network.

What was the original purpose of designing SCSI?

SCSI was originally designed to allow multiple devices to be connected to a single interface on a computer through a method called daisy chaining.

How many devices can a single SCSI chain support according to the standards?

Many SCSI standards support up to 16 devices in a single SCSI chain.

What is the newest standard of SCSI mentioned in the script?

The newest standard mentioned is iSCSI, which stands for SCSI over IP, indicating the implementation of SCSI in virtual networks.

What types of connectivity does SCSI support?

SCSI can support both parallel and serial connectivity, depending on the format used for the SCSI connection.

What were some of the devices that used SCSI before the advent of SATA and USB?

Before SATA and USB, SCSI was used to connect devices such as scanners, CD-ROM drives, and tape backup systems.

What is the benefit of the protocols used to communicate over a SCSI connection?

The protocols used over a SCSI connection are intelligent, capable of identifying the devices in the chain and managing access to those devices without additional user input.

What is the difference between a narrow and a wide bus version of SCSI?

A narrow bus version of SCSI can support up to eight different devices, while a wide bus version can support up to 16 devices.

What is a SCSI ID number used for in SCSI connections?

A SCSI ID number is used to differentiate between multiple devices connected to the same SCSI cable, with each device having a unique ID.

What is a SCSI terminator and why is it used?

A SCSI terminator is placed at the end of a SCSI cable to allow for multiple devices on the wire to communicate simultaneously without signal degradation.

What is the advantage of Serial Attached SCSI (SAS) over older SCSI configurations?

SAS simplifies the configuration process by eliminating the need to manually set SCSI IDs and install terminators, as it uses a point-to-point connection that does not require daisy chaining or terminators.

What does LUN stand for in the context of SCSI?

LUN stands for Logical Unit Number, which is used to identify individual drives within a larger SCSI ID device, such as a drive array.

How has the evolution of SCSI led to the development of serial attached SCSI?

The evolution from parallel to serial communication in SCSI, specifically with serial attached SCSI, has increased throughput and simplified implementation by using point-to-point connections without the need for daisy chains or terminators.

What is the difference between a SCSI drive and a SATA drive in terms of connectors?

While SCSI and SATA drives may look similar, the connectors on the back are different, with SCSI drives requiring a different set of connectors, such as the high-density internal SAS connector.

Outlines

00:00

🔌 Introduction to SCSI and Its Evolution

This paragraph introduces the Small Computer Systems Interface (SCSI), a standard interface for connecting various devices like storage devices, scanners, and printers to a computer network. It explains the original design for daisy-chaining multiple devices through a single interface and mentions the support for up to 16 devices in a chain. The paragraph also discusses the variety of SCSI standards and the emergence of iSCSI over IP for virtual networks. It contrasts SCSI with PATA and SATA, highlighting its support for both parallel and serial connectivity. The script delves into the history of SCSI, its intelligent connectivity, and the benefits of its protocols. It concludes with a visual description of a dated motherboard with a SCSI connector and explains the concept of SCSI ID numbers for device differentiation on the same cable.

05:04

🔄 Exploring SCSI Daisy Chaining and Termination

The second paragraph delves deeper into the practical aspects of SCSI daisy chaining, describing how devices are connected in a chain and the use of SCSI ID numbers to differentiate each device. It explains the process of assigning unique IDs to devices such as hard drives and CD-ROMs to prevent conflicts. The paragraph also introduces the concept of Logical Unit Numbers (LUNs) for identifying individual drives within a drive array. It discusses the use of SCSI terminators at the end of the cable to facilitate communication across multiple devices. The script then transitions to the newer standard of Serial Attached SCSI (SAS), which simplifies the process by eliminating the need for manually setting SCSI IDs and terminators. The paragraph concludes with a visual tour of an external SCSI storage device, showcasing its features such as power, cooling, and SCSI in/out interfaces, along with the ability to modify the SCSI ID to prevent conflicts on the same cable.

Keywords

💡SCSI

SCSI, which stands for Small Computer Systems Interface, is a standard interface used for connecting various devices such as storage devices, scanners, printers, etc., to a computer. It was originally designed to allow multiple devices to be connected to a single computer interface through a method called daisy chaining. The term is central to the video's theme as it discusses the evolution and use of SCSI in connecting peripherals. For instance, the script mentions that SCSI can support both parallel and serial connectivity and was used extensively before the advent of SATA and USB for connecting peripherals like scanners and CD-ROM drives.

💡iSCSI

iSCSI, or SCSI over IP, is a newer standard that allows SCSI to be used over IP networks. This concept is significant in the video as it represents the adaptation of SCSI to modern networking technologies, facilitating the use of SCSI in virtual networks. The script highlights iSCSI as one of the newest standards, indicating its importance in the current technological landscape.

💡PATA

PATA, which stands for Parallel ATA (Advanced Technology Attachment), is a type of interface for connecting storage devices that uses parallel data transfer. The script contrasts PATA with SCSI to illustrate the historical progression of connectivity standards, mentioning that SCSI can support both parallel and serial connectivity, with PATA being an example of parallel connectivity.

💡SATA

SATA, or Serial ATA, is a more recent standard for connecting storage devices that uses serial data transfer. The script discusses SATA in the context of the evolution from SCSI to newer connectivity standards, noting that before the widespread use of SATA and USB, SCSI was the primary method for connecting peripherals.

💡Daisy Chaining

Daisy chaining is a method of connecting multiple devices to a single interface by linking them together in a chain. The video script explains that SCSI was designed to allow for daisy chaining, enabling up to 16 devices to be connected in a single SCSI chain. This concept is crucial to understanding the flexibility and efficiency of SCSI in managing multiple devices.

💡SCSI ID

A SCSI ID is a unique identifier assigned to each device connected to a SCSI chain, allowing the system to differentiate between multiple devices on the same cable. The script explains the importance of SCSI IDs in the context of daisy chaining, where each device, such as a hard drive or CD-ROM, is given a specific ID to ensure proper communication over the SCSI connection.

💡LUN

LUN, which stands for Logical Unit Number, is a method used in SCSI to identify individual drives within a larger SCSI ID device, such as a drive array. The script uses LUNs to illustrate the granularity of SCSI's addressing system, allowing for precise referencing of storage devices within complex setups.

💡SCSI Terminator

A SCSI terminator is a device placed at the end of a SCSI cable to ensure proper signal termination and prevent signal reflection. The script describes the use of SCSI terminators in the context of daisy chaining, where they are necessary for maintaining clear communication across multiple devices on the same wire.

💡SAS

SAS, or Serial Attached SCSI, is a newer standard that simplifies the SCSI configuration by eliminating the need for manual SCSI ID settings and terminators. The script presents SAS as a more modern and user-friendly evolution of SCSI, highlighting its benefits in terms of ease of use and improved data throughput.

💡Ultra 3

Ultra 3 is a specific SCSI standard mentioned in the script, referring to an interface with a 68-pin connector. The script uses Ultra 3 as an example to illustrate the physical aspects of SCSI connections and the variety of SCSI standards that have existed over time.

💡Point-to-Point Connection

A point-to-point connection in the context of the script refers to the direct connection between a motherboard and a drive in serial attached SCSI, as opposed to the daisy chain connections of traditional SCSI. The script explains that this type of connection simplifies the setup by removing the need for daisy chains and terminators, and it enhances performance by allowing for higher data throughput.

Highlights

SCSI, the Small Computer Systems Interface, is a standard interface for connecting storage devices, scanners, printers, and other devices on a network.

SCSI was designed for daisy-chaining multiple devices to a single interface, supporting up to 16 devices in one chain.

Different SCSI standards exist with various interfaces and cables, including the newer iSCSI over IP standard used in virtual networks.

SCSI supports both parallel and serial connectivity, depending on the format used for the connection.

Before SATA and USB, SCSI was used for connecting peripherals like scanners and CD-ROM drives.

SCSI's intelligent protocols automatically identify devices in a chain and manage access over the SCSI connection.

Despite reduced popularity, SCSI is still used in some systems and extensively in virtual environments.

A dated motherboard example shows a SCSI connector alongside PATA and IDE interfaces.

SCSI ID numbers differentiate devices on the same cable, with each device assigned a unique number.

SCSI drive arrays use logical units (LUNs) to identify individual drives within a larger device.

SCSI terminators are used at the end of cables to enable communication across multiple devices.

Serial Attached SCSI (SAS) simplifies configurations by eliminating the need for manual SCSI ID settings and terminators.

External SCSI storage devices feature SCSI in and out interfaces for daisy-chaining and SCSI ID buttons for configuration.

Inside a computer with SCSI, the controller is typically set to SCSI ID 0, with hard drives daisy-chained and terminated.

Serial Attached SCSI has evolved from parallel to serial communication, increasing throughput and simplifying computer implementations.

SAS drives and arrays resemble SATA in appearance but use different connectors for high-density internal connections.

Transcripts

SCSI or what we refer to in the industry as SCSI,

is the Small Computer Systems Interface.

This is a standard interface that

can be used to connect to storage devices, scanners,

printers, and other devices on your network.

This was originally designed so that you

can have many devices connected to one single interface

on your computer by daisy chaining

multiple devices together.

And many of the SCSI standards support up

to 16 devices in one of those single SCSI chains.

This is a standard that's been around for quite some time.

So you'll find a number of different SCSI standards

with different types of interfaces

and different types of cables for each one

of these standards.

One of the newest standards is iSCSI or SCSI over IP.

And certainly, you'll find a lot of SCSI implementation

in virtual networks.

And if you look at some of the other connectivity

that we use for storage devices, such as PATA, which

is a parallel connectivity, and SATA, which

is serial connectivity, SCSI can support both parallel

and serial connectivity, depending

on which type of format you're using for that SCSI connection.

Before we had the SATA standard or was

able to use USB to be able to connect our peripherals,

we used SCSI.

SCSI was used to connect our scanners and our CD-ROM drives

and our tape backup systems.

And we had SCSI connectivity inside of our computers

and external interfaces that you could also use.

And as I mentioned earlier, you can daisy chain these devices.

So a single interface on your computer

might support eight different SCSI devices on a narrow bus,

or up to 16 if you're using a wide bus version of SCSI.

One of the benefits of SCSI and the protocols that

are used to communicate over this SCSI connection

is that it is a very intelligent form of connectivity.

You simply provide the basic connectivity,

and SCSI takes care of identifying

what devices are in that chain and how

to access those devices over the SCSI connection.

And although SCSI doesn't have the popularity

that it had in the past, you mat still

find systems that have SCSI drives or other types of SCSI

connectivity.

And SCSI as a standard is one that's used extensively

on our virtual systems.

Here's a somewhat dated motherboard

that does have a SCSI connector on it.

This motherboard also has a floppy drive

connector and an integrated drive electronics,

or IED interface.

Today we refer to these interfaces as PATA interfaces.

On the left side is the SCSI interface.

This is an Ultra 3 interface.

It has 68 pins on this connector.

If we turn the motherboard on its side,

we can see exactly the pins that are

used for this particular cable.

The cable itself is a 68 pin cable.

You can see where it plugs into the motherboard.

And you can see along the length of this ribbon cable

are connections that you can use to attach other SCSI devices.

That's 68 pin connector that we see

on the motherboard is just one of many types of SCSI

connections.

You can see that they have changed quite a bit

through the years.

And you may find that one or more of these connectors

is being used by SCSI devices that

might be in your data center.

When you have a single interface on your computer

that you're connecting multiple devices to,

you need some way to be able to differentiate between all

of these separate devices you're connecting to the same cable.

In SCSI we're able to accomplish this by using a SCSI ID number.

So every device you would connect to that particular SCSI

cable would all have a separate ID number associated with it.

So your computer might be a SCSI ID 0.

You might be connecting to your computer

a hard drive on that cable.

That can be assigned an ID number of 2.

And you might have another device on that cable,

such as CD-ROM, and you would assign a separate SCSI ID

to that device, for example SCSI ID 3.

If you think about connectivity to a drive array,

it's a single chassis with many different drives inside of it.

Because of this, SCSI has a method,

not only to identify the chassis of that drive array

through a SCSI ID, but we can identify individual drives

by a logical unit or LUN.

That logical unit allows you to reference a single drive

within a much larger SCSI ID device.

It's also very common on this cable

that at the end of the cable you place a SCSI terminator.

The SCSI terminator allows you to have multiple devices

on this wire and still be able to communicate

across all of those devices simultaneously.

One of the more recent standards for SCSI

is a serial attached SCSI or SAS.

These devices are much simplified over the older SCSI

configurations that require you to manually set a SCSI ID

and to always have a terminator on the connection.

With these newer SAS devices, you

don't have to worry about setting jumpers for SCSI IDs.

You don't have to install any terminators

or make any additional settings to be

able to use those serial attached SCSI devices.

Here's the back of an external SCSI storage device.

You see we have a spot for power.

Looks like there's a fan inside of this device

or some type of cooling.

And here are the SCSI interfaces,

one that is a SCSI out and one that is a SCSI in.

This is how you would be able to daisy chain

this particular device along with other SCSI

devices on the same cable.

This SCSI device has been assigned a SCSI ID of 6.

And you can see there are buttons on this device that

allow you to modify the SCSI ID to prevent any conflicts

on that same cable.

So if you look inside of a computer that

has a SCSI controller and multiple SCSI hard drives,

you'll probably see the SCSI controller

set to a SCSI ID of 0.

And then there's probably a cable

from that device that goes to the first hard drive.

And that drive is daisy chained to, in this case,

a second hard drive.

And then at the end of that cable is a SCSI terminator.

This is what the SCSI terminator looks like that is connected

to the end of that SCSI cable.

So if you look inside one of these computers

with SCSI interfaces, you may find a cable

that looks something like this.

You can see that it plugs into the motherboard.

It's got a long set of cables.

Here's one connector for a storage device.

Another connection, a third, a fourth,

and then finally a terminator at the end of this cable.

So inside of the computer we would use a cable

like that to connect to the motherboard.

And then one of those other connectors

would connect to the SCSI drives that are inside of our system.

Here's a view of the SCSI connection

outside of a computer case.

You can see the motherboard is on the top with that SCSI

connector.

And that single ribbon cable wraps around.

And one of the interfaces on that ribbon cable

connects to a storage drive.

You can see there are multiple interfaces on this cable.

So we can continue to add storage drives as long as we

have connectors on this cable.

In our next video, we'll talk about how

we moved from the PATA or parallel communication

to SATA or serial communication.

And SCSI has had a very similar evolution.

One of the more recent standards for SCSI

is the serial attached SCSI where

we went from parallel communication

to a serial communication.

This not only increased the total throughput

that we could have in our systems,

but it greatly simplified the implementation

in our computers.

Because this is a point to point connection

between the motherboard and the drive.

We no longer have these cables with multiple interfaces

or devices with multiple SCSI interfaces,

because there's no more daisy chains.

We also removed the need to have a terminator,

because the only thing on the serial

attached SCSI connection is the controller on one side

and the hard drive or storage device on the other.

This gives us the control and management

of a well-established SCSI set of protocols,

but it also provides us with the speeds we need for our most

modern storage devices.

Here's a serial attached SCSI drive.

You can see it looks very similar to a SATA drive.

But the connectors on the back are slightly different,

and they do require a different set of connectors.

An example of this very large connector

that is a high density internal SAS

connector that you would use inside of your computer.

And of course, there are also serial attached SCSI arrays so

that you can connect many different serial attached

SCSI drives into this single chassis.