SCSI Device Cables - CompTIA A+ 220-1101 - 3.1
Summary
TLDRThis 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
- π SCSI stands for Small Computer Systems Interface, a standard interface for connecting various devices like storage, scanners, and printers.
- π SCSI allows for daisy-chaining multiple devices, supporting up to 16 devices in a single chain, enhancing connectivity efficiency.
- π iSCSI, or SCSI over IP, is a newer standard that enables SCSI implementation in virtual networks, adapting to modern connectivity needs.
- π SCSI supports both parallel and serial connectivity, offering flexibility in how devices can be connected depending on the format used.
- π¦ Before SATA and USB, SCSI was the primary method for connecting peripherals like scanners and CD-ROM drives, highlighting its historical significance.
- π‘ SCSI is intelligent, automatically identifying devices in a chain and facilitating access without manual configuration by the user.
- π Despite its decline in popularity, SCSI is still used in certain systems, especially in virtual environments, showing its enduring utility.
- π© The script describes a SCSI Ultra 3 interface with a 68-pin connector, illustrating the physical aspects of SCSI connectivity.
- π SCSI uses unique ID numbers for each device in a chain to differentiate and manage multiple devices connected to the same interface.
- π 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.
- π Serial Attached SCSI (SAS) is a recent standard that simplifies SCSI configuration by eliminating the need for manual ID setting and terminators.
- π 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
π 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.
π 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.
Mindmap
Keywords
π‘SCSI
π‘iSCSI
π‘PATA
π‘SATA
π‘Daisy Chaining
π‘SCSI ID
π‘LUN
π‘SCSI Terminator
π‘SAS
π‘Ultra 3
π‘Point-to-Point Connection
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.
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