What internal device does a computer use?

Direct-attached storage (DAS) is a type of storage that is attached directly to a computer without going through a network. The storage might be connected internally or externally. Only the host computer can access the data directly. Other devices must go through the host computer to work with the data.

Inhaltsverzeichnis Show

Direct-attached storage pros and cons
What are the differences between SAN, NAS and DAS?
Security issues with direct-attached storage
Future DAS outlook and trends
Internet Connection Components and Functions
General Networking Physical Components and Functions
VDSL and ADSL
Home Routers Without a Land Line
Dual Routers (VDSL/ADSL/Fibre) + Mobile
Mi-Fi -BroadBand Wi-FI Hub
Cable Coupler/Extender and Splitter
Networking and Internet Services
Common Networking Terms and Acronyms

Most servers, desktops and laptops contain an internal hard disk drive (HDD) or solid-state drive (SSD). Each of these devices is a form of direct-attached storage. Some computers also use external DAS devices. In some cases, an enterprise server might connect directly to drives that are shared by other servers.

A direct-attached storage device is not networked. There are no connections through Ethernet or Fibre Channel (FC) switches, as is the case for network-attached storage (NAS) or a storage area network (SAN).

An external DAS device connects directly to a computer through an interface such as Small Computer System Interface (SCSI), Serial Advanced Technology Attachment (SATA), Serial-Attached SCSI (SAS), FC or Internet SCSI (iSCSI). The device attaches to a card plugged into an internal bus on the computer.

Other types of storage, such as optical devices and tape, are technically DAS as they are directly attached to a system, either internally or externally. However, references to DAS are usually related to storage devices such as HDDs or SSDs.

How DAS works

Direct-attached storage pros and cons

DAS can provide users with better performance than networked storage because the server does not have to traverse a network to read and write data, which is why many organizations turn to DAS for applications that require high performance. DAS is also less complex than network-based storage systems, making it easier to implement and maintain, and it is cheaper.

DAS is not without challenges, however. It has limited scalability and lacks the type of centralized management and backup capabilities available to other storage platforms. In addition, it can't be easily shared and doesn't facilitate failover should the server crash. Because of these challenges, conventional forms of DAS might not be suited for many enterprise workloads.

However, advancements in virtualization technologies have breathed new life into DAS, a trend that's been especially apparent in the many hyperconverged infrastructure (HCI) systems now on the market. An HCI system is made up of multiple server and DAS storage nodes, with the storage consolidated into logical resource pools, providing a more flexible storage solution than conventional DAS.

What are the differences between SAN, NAS and DAS?

NAS and SAN are networked storage systems that pool storage capacity and share it with application servers over a high-speed network.

In contrast, DAS attaches directly to the servers, which means connectivity and expandability are both constrained by the number of expansion slots in the server. The size of the DAS enclosure also restricts storage capacity, and DAS is typically limited to a small number of ports or host connections, making it more difficult to share storage resources.

In addition, DAS often lacks many of the more advanced storage management features common to NAS and SAN systems, such as remote replication and snapshots. Although virtualization, HCI and other innovations are reinvigorating DAS, they also come with their own limitations.

DAS vs. NAS and SAN

On the plus side, DAS is less expensive than SAN or NAS and is easier to deploy when directly plugged into a server. Administrators need only connect a new drive to a server to increase storage capacity by as much as several terabytes. This has made DAS a practical storage choice for many small- and medium-sized businesses (SMBs), where storage costs and administrative overhead are considerations.

Even when organizations use NAS or SANs, most physical servers continue to boot from DAS storage. The speed of SSDs, in particular, makes booting locally more efficient than networked storage. Thanks to local SSDs, a physical server can often boot in only a few seconds.

This speed can be especially useful when a physical server hosts virtual machines that need to start up quickly in the event of a crash or after scheduled downtime for service or maintenance.

Security issues with direct-attached storage

As with all storage systems that host an organization's critical applications and data, security is a prime consideration when planning storage. To protect data stored on direct-attached storage, users should do the following:

Perform an in-depth security assessment of your DAS environment to discover weaknesses. You might discover vulnerabilities such as lax user permissions, missing patches or misconfigured systems.
Run an audit of user permissions. In addition, scan the DAS devices for unstructured information accessible to everyone on the network. Once that's done, lock down permissions. Also consider segmenting your network to better protect critical DAS systems.
Make patching a priority. Not keeping up with operating system and application software patches can leave your DAS vulnerable to malfeasance. An intruder who gains access to the DAS host can access all data on that system, and organizations may not even know the system has been breached.
Conduct business continuity and fault tolerance testing by checking the resiliency of the DAS system. Focus on realistic system scenarios, such as storage hardware failures or the data center being damaged or destroyed.

Future DAS outlook and trends

Three important technologies have come together to enable DAS to deliver exceptional performance: flash-based SSDs, non-volatile memory express (NVMe) and Peripheral Component Interconnect Express (PCIe).

Over the years, flash storage has gotten faster, denser and cheaper, but the traditional storage interfaces -- particularly SATA and SAS -- could not take full advantage of flash's capabilities. This led to the development of NVMe, a logical device interface for direct-attached PCIe storage devices.

NVMe has been architected for higher-performance SSDs. It accelerates performance by exploiting PCIe parallelism through an optimized command set. PCIe is now in its fourth generation, with PCIe 5.0 just around the corner.

Flash SSDs are not the only devices to benefit from the NVMe/PCIe combo. Storage class memory devices such as Intel's Optane SSDs are based on the 3D XPoint technology codeveloped by Intel and Micron Technology. The Optane SSDs offer higher throughput, lower latency, greater density and improved endurance over NAND flash technology. They're also more expensive.

An Internet connected home/home office network, consists of a variety of hardware and software components.

In this tutorial we look at the various components that you need to create a computer network and connect it to the Internet.

At the end of the tutorial you should understand what devices are required to create a home network and what functions they serve.

You should also understand the Internet services that are essential for connecting to and using a home network and the Internet.

Internet Connection Components and Functions

The diagram below shows a typical home or small office network layout.

DSL Modem–

This converts digital signals into analogue signals that are suitable for sending over a telephone line. It is usually built into the Internet/broadband router and not normally purchased as a separate component.

DSL/Broadband Filter

Used to filter out DSL signals from telephone signals so that you can access the internet and use the telephone simultaneously.

Firewall and NAT Router

A firewall functions like a router except that it blocks traffic from the external network according to user configured rules.

A firewall protects your home/small business network computers and devices from intruders on the Internet.

It effectively acts like a one way digital gate blocking access to your network from devices on the Internet, but at the same time allowing devices on your network to connect to devices on the Internet. (schematic below)

Small networks use a firewall/NAT router combination in which a single device acts as a NAT router and firewall.

NAT effectively isolates your home network from the Internet.

See Port forwarding and Internal and external IP Addresses.

Computer Firewalls –

If you are using Windows XP (or above) then you also will have firewall on your computer.

This firewall is less secure than the one built into your router/hub but it is normal to leave it enabled on your computers.

When you install applications e.g. Skype you will find that they change the firewall settings.

Here is a short video explaining how the computer firewall works.

ICS (Internet Connection Sharing)-

Internet connection sharing allows you to share an Internet connection with other computers on a Local/home Network.

It requires that one computer be designated as the sharing computer (the computer with the Internet connection).

This computer functions effectively as a NAT Router, and must be left switched on for the other computers to access the Internet.

This configuration is not normally used anymore.

General Networking Physical Components and Functions

Hubs,bridges and switches are all devices used to connect computers and other devices together on an Ethernet network.

Network Hub

A hub connects two or more computers together (like switch in diagram above).

Hubs are effectively multi port repeaters and operate at the physical layer (level one). They do not examine the network traffic. They are being replaced today by the switches. Smallest is usually 4 port.

Network Bridge

A bridge connects two network segments together and is a selective repeater. It examines the MAC address of the traffic it sees and learns which network segments contain the various MAC address.

It uses this information to decide whether or not to repeat the traffic on a network segment.

A Bridge works at level 2 (data link Level) and will transmit broadcasts.

Bridges are also being replaced by switches

Network Switch

A switch Connects two or more computers together and used today in preference to a hub or bridge.

Like a bridge a switch learns about MAC address connected to each port and will only send data on that port that is addressed to those MAC addresses.

A switch is effectively a bridge with more ports.

Using switches usually speeds up a network but it depends on the network configuration. See the Basic networking Course

There are various types being sold marketed as unmanaged,managed and smart.

A basic unmanaged switch requires zero configuration. You just insert it into the network.

A managed switch gives you full control of the switch and usually out of the box behaves like an unmanaged switch. You can however control the switch,configure the Ports etc. These types are not normally used on home networks due to the complexity and there being little need.

A smart switch is somewhere in between a managed and unmanaged and is found on home networks requiring VLANs.

POE Switch

Many modern switches provide POE ports. This allows you to power devices. like cameras. directly from the switch without the need of an external power supply on the camera. See POE explained for beginners

Wireless Access Point

A wireless access point connects wireless devices to an Ethernet network, and to each other.It effectively does the same job as a hub/switch but for wireless devices.

Many Access points can be powered using POE (Power over Ethernet) which means that they can be placed in positions where there is no mains connection making them very flexible. See POE explained for beginners

PoE Injector

These are used to connect a PoE end device to a non PoE device like a legacy switch. The legacy switch cannot provide the power so the injector does.

PoE Splitter – This Splits the data from the power and is used to connect a non PoE end device to PoE source.

The power extracted by the splitter is often used to power the device using a separate power input.

The one shown is the DSLRKIT Active PoE Splitter used to power the Raspberry Pi.

Home Routers

A router connects networks together. Routers operate at the networking level of the TCP/IP protocol stack.
On Home networks the router is responsible for connecting the home network to the Internet and provides several important networking services like:

Most home routers provide both Wi-Fi and Ethernet connections.

Home routers also provide NAT (Network Address translation) services.

They are also commonly known as hubs but this doesn’t actually describe their networking role.

Home Router Internet Connection Types

A router connects two networks together.

In the case of an home router the networks are the Internet and the home network as shown in the diagram below.

There are four main Internet connection types in use

ADSL – old
VDSL – Used with Fibre to cabinet connections (FTTC)
Fibre – Used with FTTP
Cable – Cable networks

If you purchase your own router then you need to ensure it is the correct type for your Internet connection.

Routers and Modems and Filters

If you look at the internet connection diagram above you will see a broadband filter.

This filter is necessary on ADSL and VDSL connections, but is now commonly included in the ISP socket.

However you will need to check your socket type to determine this.

What isn’t shown is a modem.

A modem, if required, is placed between the router and the internet connection.

External modems are commonly found on Networks that connect using fibre, and are required to convert electrical signals from the router into light signals to send over the fibre cable.

VDSL and ADSL

Internet connections that use telephone cables to connect to the Internet use these link protocols or technologies.

ADSL (Analogue digital subscriber line) is the older technology, and is now being replaced by VDSL (very high speed digital subscriber line) which is faster.

VDSL isn’t fibre, but it is used in conjunction with fibre in what is know as fibre to the kerb connections.

In these connections the fibre is provided to a distribution point near the home, and the standard telephone lines provide the connection to the home using VDSL.

Home Routers Without a Land Line

Traditionally Internet connections have required a land line connection.

However more and more people are not using a traditional land line phone connection, but a mobile phone.

There are many home routers on the market that support 3G and 4G mobile networks.

They were originally designed for use by mobile workers or people on holiday that required to share a mobile Internet connection.

Usually they provide a Wi-Fi access point and Ethernet connections just like a traditional home router but the connection to the ISP is via the mobile network as shown below.

Before you purchase one for home use you should check the network availability in your area.

The upload and download speeds are generally slower than land line with 3G giving between 200kbps and 7.2Mbps.

4G giving 8-10 Mbits/s (quoted speeds) in the UK but published speeds are much higher with 4G having maximum download speed of around 160Mbits/s.

Here is a screen shot from the ee mobile provider.

See Mobile routers for more details

Dual Routers (VDSL/ADSL/Fibre) + Mobile

Many routers now provide two Internet access methods for redundancy purposes and are increasing popular with the current work at home trend.

The main connection is usually VDSL/ADSL or fibre but when this fails it will fall back to the mobile connection automatically.

Providing two internet connection methods on a home is also possible using a standard home router and standalone 3G/4G router but in this case you would need to make changes to you client to use the 3G/4G connection as it wouldn’t be automatic.

Wi-Fi Range Extender/Repeater

Place in range of the existing Wireless network, and it will take the signal from the network and rebroadcast it, thus increasing the range of the network.

Modern ones plug directly into a mains socket and require no other connections.

Note: see Wi-Fi homeplug adapters below.

Mi-Fi -BroadBand Wi-FI Hub

A Mi-Fi Hub is a relatively new device, and it can be used for connecting multiple devices to the Internet over the mobile network (3g and 4G).

Your devices connect to the hub using Wi-Fi and the Hub connects to the mobile network using 3G/4G .

Mi-Fi hubs are low cost ( around £20 to £40) and many will work hours without being connected to the mains.

You will need a Sim and a mobile data plan.

Homeplug Adaptor

These are Ethernet cards that plug directly into a mains socket, and use the mains wiring to carry the Ethernet signal instead of using UTP cable.

They come in pairs and you need a minimum of 2 adapters.

They plug into the mains and have an Ethernet socket that you can use to connect to a computer,switch , router etc.

You can also get ones that function as Wireless Access points which are used for extending a networks to overcome range limitations of Wi-Fi.

These look like a normal homeplug adapters but have a wireless access point built in.

See Homeplug adaptors and Powerline networking and extending a home network.

Wi-Fi Range Extender/Repeater vs Wi-Fi Homeplug

A Wi-Fi range extender needs to be in range of an existing Wi-Fi network to work.

A Wi-Fi homeplug adaptor needs to be connected to another homeplug adapter using the electrical mains.

Wi-Fi homeplug adaptors give you much better performance than range extenders.

UTP (Unshielded Twisted Pair) Cables

Common cable for connecting Ethernet devices together.Ranges from CAT5 to CAT6.

Older Installations will use CAT5 and newer ones CAT6, which is designed for higher speeds.

Here is a good video covering the differences between UTP and STP, straight vs crossover, and the different categories.

Wiki On cat6 cable and cat 5.

See How to Wire your Home Network

Ethernet Crossover Cable

Used to connect two computers together without requiring a hub/switch.

It is also used for connecting older hubs/switches in cascade. Not normally required today as the newer hubs/switches use auto detect and can switch modes.

See Wiki on Ethernet crossover cable and Medium dependent interface

Cable Coupler/Extender and Splitter

Low cost and very useful for joining Ethernet cables together.

Simply Plug an Ethernet cable into each socket.

You can also use an Ethernet splitter to extend a cable, and provide more Ethernet sockets,

Connector are RJ45

Useful Resources:

How to wire your own home network PCworld tutorial and This video .

Networking and Internet Services

Just having computers connected together by WI-FI or Ethernet is the first step. To exchange information they require to have, and use several networking services and protocols.

The main ones are:

IP protocol

All modern networks use the IP networking protocol, and to work on a network all devices require an IP address.

There are two versions of the IP protocol currently in operation.

IPv4 is the original version and is deployed in all home and office networks and on the Internet.

IPv6 is being rolled out and many new networks and network devices support it, but it isn’t used as the default protocol.

DHCP (Dynamic Host configuration Protocol)

DHCP is a service and protocol that requests and assigns IP addresses to computers automatically.

All modern computers,tablets and smart phones are capable of using DHCP and are configured to use it by default.

For home and small office networks the DHCP service is built into the router that connects to the Internet.

For larger office networks this service is configured on a network server.

If no DHCP service is available clients will automatically assign their own IP address (known as a local address) or you can manually assign them( called static addresses).

See understanding DHCP on Home Networks

DNS (domain Name Service)

The domain name system is the heart of the Internet. It is responsible for resolving domain names to IP addresses.

Without DNS you would have to remember the IP address of each website that you visited.

All networking clients (PCs,tablets,Phones) function as DNS clients and have the necessary software built in so that they can use DNS.

The DNS servers store the data and are mainly located on the Internet e.g. your ISP (internet service provider,Google etc).

Large companies will use their own DNS servers locally.

To use DNS the client will need to know the address of a DNS server. This is normally assigned by the DHCP server.

See Understanding DNS

Search Engines

DNS is crucial to the Internet and search engines are crucial for the Web.

For most people the process goes like this

Use search engine search e.g.Google
Click on desired link.
Web browser uses DNS to locate the IP address of the website. (not visible to user)
Browser displays content from website.

Common Networking Terms and Acronyms

MAC Address – The 64 bit Physical address of the device which is assigned to the Wi_fi adapter or NIC. Cannot normally be changed.

NIC– Network Interface card. Ethernet card found in computers

UTP- (Unshielded twisted pair)- Common cable for connecting network devices.

RJ45- Connector used for connecting Ethernet devices.

RJ11- Connector used for connecting telephones,modems etc in USA and adopted in other countries.

Gateway – A gateway works at the application level of the TCP/IP protocol stack and does a translation. Examples are email to FAX gateways.

On earlier networks and in earlier networking courses routers were called gateways, and the term is still used when setting up networking clients.

In this context the term gateway refers to the gateway to an external network i.e. the Internet.

Uni-cast Message – Message sent from one device to another.

Multicast Message -Message sent from one device to several others.

Broadcast Message -Message sent to all nodes on the network.

Quick Quiz

Q1 – Which device is not required to connect to the Internet connection?

Q2-Which of the following components is not required for a home network?

Router
Switch
Wireless Access point
Ethernet crossover Cable

Q3 -What hardware is essential to creating a home wi-fi network?

Router
Switch
Wireless Access point
Ethernet crossover Cable

Q4 -A gateway is a common network hardware component that does what?

Connects several computers together.
Resolves names to IP addresses
Assigns IP addresses
Connects a network to the Internet.

Related Articles

Answers

Q1-A switch.

Q2- Ethernet crossover Cable

Q3 -Wireless Access point

Q4- Connects a network to the Internet.

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