Redundant Array of Independent Disk (RAID)


The Term “RAID” was used in 1987 by David Patterson, Garth A. Gibson and Randy Katz at the University of California, Berkeley in 1987.  In their 1988 report, “A Case for Redundant Arrays of Inexpensive Disks (RAID)” they argued that the mainframe disk drives performance can be beaten by RAID. By configuring redundancy, the reliability is beyond to any extent single drive.


The term RAID related to hard disk management technique mostly for server side.  RAID is a data storage virtualization technology that combine multiple hard disk into a single logical unit for data redundancy, reliability and performance improvement.  It has used mirroring, stripping and/or parity to achieve the RAID configuration.  Once the RAID is setup, it forms a single logical disk for the operating system.


In Stripping, hard disk divided into blocks and these blocks are stacked together and called strips. With multiple hard disks placed parallel or serial, we can achieve the stripe. Without mirroring and parity, Stripping cannot have safe data but stripping may significantly improve the I/O performance.



Mirroring is most trusted method for data protection in RAID.  This is straightforward way to understand as it copies identical data onto more than one drive in real time. It most commonly used in RAID 1. In case the first disk failure, the controller uses the second disk to serve the date, and it makes the data available continuously without any disruption.

When the failed disk is replaced with a new disk, the controller copies the data from the surviving disk of the mirrored pair. Data is simultaneously recorded on both the disk. Though this type of RAID gives you highest availability of data but it is costly as it requires double amount of disk space and thus increasing the cost.



This is reliable and low-cost solution in RAID for data protection. In this method, an additional disk is added to stripe width to hold parity bit.  Parity used for fault tolerance by calculating the data in two drives and storing results on third drive.  RAID 3 used parity disk for fault tolerance and fast data stripping.

The parity bits are used to recreate the data during the disk failure.  Parity information can be stored a separate disk or can be stored across all disks.


RAID Controllers

A RAID controller is a hardware or software program used to manage the hard disks in storage array so that they can be as a logical unit.  RAID controllers bridge between the operating system and the hard disks.

In hardware-based RAID, physical controller is used at motherboard or at separate RAID card to present the data to the applications and operating systems as logical units. The controller resides on a PCI bus.

In Software RAID performs the processing on the host’s CPU.  Thus, it gives a cheapest possible solution.  The difference between the hardware RAID and software RAID is where the RAID processing happens. Software-based RAID does not use the server processor and hardware-based RAID provides better performance. Hardware-based RAID is more expensive than software based RAID due to its additional hardware.


Standard RAID levels


RAID 0 knows as stripping.  Data split and stored across two or more disks, without any parity, redundancy or fault tolerance.  Since RAID 0 has no fault tolerance, the failure of one disk will cause the entire array to fail.

  • Minimum 2 disks.
  • No redundancy
  • Do not use for mission critical applications.




In RAID 1, data is writing simultaneously in two disks. It consists of exact set of data (mirror) on two or more disks.  If one disk failed, the data can be retrieved from the other disk.

This layout is useful when read performance or reliability is more important than write performance or the resulting data storage capacity.

  • Minimum 2 disks.
  • Excellent redundancy
  • Good performance
  • Do not use for mission critical applications.




RAID 2 is rarely used in practice, it stripes data at the bit level rather than block level. It uses a hamming code for error connection.








RAID 3 also rarely used in practice, it stripes data at the byte level with a dedicated parity disk.  RAID 3 cannot serve multiple request simultaneously.







RAID 4 stripes data at the block level with a dedicated parity disk. RAID 4 provides superior performance of random reads, while the performance of random writes is low due to the need to write all parity data to a single disk.







RAID 5 consist of block level stripping with distributed parity. In RAID 4 parity information is distributed among the disks. It requires that all drives but one be present to operate.

Upon failure of a single drive, subsequent reads can be calculated from the distributed parity such that no data is lost.

  • Minimum 3 disks.
  • Good redundancy
  • Good performance
  • Use for databases that is heavily read oriented. Write operation is slow.



RAID 10 also known as RAID 1+0. It combined disk mirroring and disk stripping to protect the data. If one disk in each mirrored pair is functional, data can be retrieved.


  • Minimum 4 disks.
  • Excellent redundancy
  • Excellent performance
  • Best option for mission critical applications especially databases.





Ransomware Cyber Attack

What is Ransomware?
Ransomware is a cyber attack by wannacry malware for those computers are connected to the internet. This is mainly targeted on Microsoft Windows Operating Systems by encrypting the user files in a way that can’t access it anymore and demanding some money in the Bitcon crypto currency. The attack was beginning on 12th May 2017 and affected many companies like British hospital and Spanish companies like Telefonica etc. This worm has attacked over 200,000 computers in 150 countries.

How it affects?

Email link and email attachment account for 59% of Ransomware attack. Users are more prone by clicking the links than accessing an infected website.  Attackers send the wannacry worm emails to users to ask them to click or download the attached file. When user click the link, or download the files from emails the worm enter the computer.Email link and email attachment account for 59% of Ransomware attack. Users are more prone by clicking the links than accessing an infected website.  Attackers send the wannacry worm emails to users to ask them to click or download the attached file. When user click the link, or download the files from emails the worm enter the computer.

Wannacry malicious ransomware worm targets computers are running Microsoft windows operating systems. Wannacry spread by using EternalBlue, an exploit of Windows SMB (Server Message Block) Protocol.  It installs the DoublePulsar, a backdoor implant tool, which then transfers and runs the Wannacry ransomware package. Once the package installed it will encrypt all data by converting that .crypt file format, when try to open the file, it redirect to the payment option. Also, it scans the vulnerable systems then use the EtenalBlue an exploit to gain access and spread itself to the computer network and affect all files.

Security experts warns that there will be no guarantee that the access will be granted after payment.

How to prevent it?

  • The first option is try not to click the email link which is send by unknown person. Also try not to download any documents from unknown person.
  • Update your Operating System updates from Microsoft.
  • Ensure your network firewall and antivirus software is up to date.
  • Those are using Office 365, subscribe Work Plus ATP (Advance Threat Protection) from Microsoft.
  • Do regular backup of your working files and keep in separate place which is not connected to your current network.
  • Ensure your email server provide spam filter is working good.
  • Discovered ‘kill switch’ for Ransomware attack. It slows down the wannacry malware spread
  • Microsoft issued critical security patch on 14 March 2017 to remove the underlying vulnerability on supported versions of Windows.

NAT & Double NAT


There are 4 billion IP addresses are available in IPv4 (32 bits) network. If each person connect to the internet using individual IP address, the current IP addresses in IPv4 (4,294,967,296) is not enough. Network Address Translation (NAT) concept was introduced to solved this IP address issue.  The router get only one public IP address from ISP and all other connected devices gets the private IP address, it usually start with 192.168.0 or 10.0.0.  NAT converts all private IP address request and send outside the world using one public IP address.  With this, a home or an organization needs only one public address to connect the internet. Router are distributing private IP addresses using DHCP function.


Double NAT means multiple devices on the network are performing NAT functions. Example for this is, WiFi Routers are connected with the ISP Modem / Routers. It won’t prevent you to connect the internet, but sometimes it will create issues for VPN connections, accessing SSL websites, online games, and accessing other private network.

Solutions for Double NAT:

  • Enable Bridge mode in wireless router
    • Login to wireless router admin page in web-browser
    • Settings page, enable the bridge mode or disbale NAT and DHCP functions.
  • Set wireless router in modem’s DMZ
    • Login to wireless router admin page and find the WAN IP Address
    • Login to modem and go to DMZ settings.
    • Add wireless router, WAN IP address in DMZ settings.
  • Setup PPPoE between modem and wireless router
    • set PPPoE in wireless router.
    • PPPoE will bypass the NAT in the modem.

Router’s common issues

Routers are mandatory for small businesses and homes to connect the outside world.  Wireless routers are common for home and all types of businesses to get the internet connection to their desktops, laptops, smart phones, tablet devices and other wireless devices. Router determines how to send and where to send the information from one computer to another computer.  The information can be send from one network to another network as well.

Common issues of routers are:

  • Difficult configurations
  • Firmware updates
  • Hardware specs (Memory, HDD etc)
  • no. of simultaneous users

Common issues of Wireless routers are :

  • Interference (Positioning of router).
  • Distance between Wireless Access Points and client devices.
  • Router capacity for concurrent users.

Best ADSL Router

TP Link AC1750 Wireless Dual Band Gigabit ADSL2+ Modem RouterArcher D7

  • Supports Superfast Wireless Speed with 802.11ac standard
  • Dual band
  • 3 dual band detachable external antennas
  • Full Gigabit Wired Connection
  • One Gigabit LAN/WAN port
  • Three Gigabit LAN ports
  • Simultaneous 2.4GHz 450Mbps and 5GHz 1300Mbps connections provide a premium wireless experience
  • Share a printer locally and files & media with networked devices or remotely via FTP server
  • Ethernet WAN (EWAN) port accepts connections from cable and fiber modems via Ethernet cable
  • TP-LINK Tether provides the easiest way to access and manage the router on your iOS and Android devices

Wireless Access Point Positioning

Placement of WiFi access point is most important in WiFi infrastructure design for optimizing nework.  It will reduce the hassle for IT staff after deployment of wireless access point setup.  Poor installation of WiFi will cause connectivity issue and lead to customer dissatisfaction.

The following tips helps to place a access points for better performance:

Free from obstacles

Try to place wireless access points without any obstacles such as wall, furniture, ceiling etc.  So that the Radio Frequency waves can be reach the client device faster speed.


Access point placement on ceiling is best for horizontal coverage. If ceiling is too high try no to do. Do not put Access point above the ceiling tiles. It will create a extra barrier to go through the signal.

External antenna

Do not point external antennas all in one direction.


Avoid interference with the bluetooth devices, microwave ovens, fluorescent light bulbs, cordless phones, and other WLAN networks devices.


Types of Wireless Networks

Wireless network connections replaced cables to connect internet for laptops, smart phones and tablet devices using radio frequency waves.  With wireless connections smartphones and tablet devices are conveniently access internet connections without cables.  Second-generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland in 1991.


Type Range Standards Performance Applications
Wireless Personal Area Network (WPAN) Within reach of a person Bluetooth, NFC, Wireless USB, ANT UWB & ZigBee Moderate Cable replacement for peripherals.
Wireless Local Area Network (WLAN) Within a campus or building IEEE 802.11 High Wireless extension of wired network.
Wireless Metropolitan Area Network (WMAN) Within a city IEEE 802.15 (WiMAX) High Wireless inter-network connectivity
Wireless Wide Area Network (WWAN)


Worldwide Cellular Low/Moderate Wireless network access.


Apple introduces New 9.7-inch iPad

March 21, 2017

All of the Fun and Power of iPad, Now Starting at $329

Apple updated its most popular-sized iPad, featuring a brighter 9.7-inch Retina display and best-in-class performance at its most affordable price ever, starting at $329 (US). Designed for unmatched portability and ease of use, along with incredible performance and all-day battery life, iPad is the world’s most popular tablet and the primary computing device for millions of customers around the world. Through the more than 1.3 million apps designed specifically for iPad, customers can do even more, from learning to code with Swift Playgrounds and reading books on the large screen to boosting productivity through Microsoft Office and using multitasking features like Split Screen.

“iPad is the world’s most popular tablet. Customers love the large, 9.7-inch display for everything from watching TV and movies, to surfing the web, making FaceTime calls, and enjoying photos, and now it is even more affordable,” said Philip Schiller, Apple’s senior vice president of Worldwide Marketing. “New customers and anyone looking to upgrade will love this new iPad for use at home, in school, and for work, with its gorgeous Retina display, our powerful A9 chip, and access to the more than 1.3 million apps designed specifically for it.”

iPad features a beautifully bright Retina display with over 3.1 million pixels for stunning pictures and videos, and is enclosed in a sturdy yet thin aluminum unibody enclosure weighing just one pound for great portability and durability. The Apple-designed A9 chip with 64‑bit desktop-class architecture delivers fast processing and graphics performance for apps and games, while maintaining the same all-day battery life1 customers have come to expect from iPad.

The front- and back-facing cameras offer exceptional low-light performance and HD video recording, making it fun and easy to FaceTime with friends and family and capture unforgettable memories using the large Retina display as a viewfinder. Ultrafast wireless means connecting with iPad is quick and easy, and support for LTE cellular bands worldwide helps customers stay connected when traveling.2 Apple SIM makes it even easier to connect to wireless data plans right from your device when traveling in more than 140 countries and regions.
Touch ID gives iPad users a simple and secure way to unlock iPad, keep personal information private within apps and approve purchases from the App Store, iTunes Store and iBooks Store. With Apple Pay3 on iPad, paying for physical goods and services within apps or on a website in Safari has never been easier.
iPad comes with iOS 10, which brings more expressive and animated ways to communicate in Messages, new ways to use Siri with your favorite apps, beautifully redesigned Maps, Photos, Apple Music and News, and the new Home app, which lets you simply and securely set up, manage and control your home all in one place. Multitasking features including Slide Over, Split View and Picture-in-Picture help you do even more.
source : 

Apple introduces iPhone 7 and iPhone 7 Plus (PRODUCT)RED Special Edition

Customers Can Now Purchase iPhone in a Beautiful New Finish and Contribute to the Global Fund to Fight AIDS.

Apple announced on March 21, 2017 iPhone 7 and iPhone 7 Plus (PRODUCT) RED Special Edition in a vibrant red aluminum finish, in recognition of more than 10 years of partnership between Apple and (RED). This gives customers an unprecedented way to contribute to the Global Fund and bring the world a step closer to an AIDS-free generation. The special edition (PRODUCT) RED iPhone will be available to order online worldwide and in stores beginning Friday, 2017 March 24.

“Since we began working with (RED) 10 years ago, our customers have made a significant impact in fighting the spread of AIDS through the purchase of our products, from the original iPod nano (PRODUCT)RED Special Edition all the way to today’s lineup of Beats products and accessories for iPhone, iPad and Apple Watch,” said Tim Cook, Apple’s CEO. “The introduction of this special edition iPhone in a gorgeous red finish is our biggest (PRODUCT)RED offering to date in celebration of our partnership with (RED), and we can’t wait to get it into customers’ hands.”

“Apple is the world’s largest corporate donor to the Global Fund, contributing more than $130 million as part of its partnership with (RED),” said Deborah Dugan, (RED)’s CEO. “Combining the global reach of the world’s most loved smartphone with our efforts to provide access to life-saving ARV medication in sub-Saharan Africa, customers now have a remarkable opportunity to make a difference and contribute to the Global Fund through the purchase of this new beautiful (PRODUCT)RED iPhone.”
iPhone 7 and iPhone 7 Plus are the best, most advanced iPhones ever, packed with unique innovations that improve all the ways iPhone is used every day. Both phones feature the most popular camera in the world with advanced camera systems that shoot incredible photos and videos day or night, more power and performance with the best battery life ever in an iPhone, immersive stereo speakers and a wide color system from camera to display, all in a water and dust resistant design. iPhone comes with iOS 10, which brings more expressive and animated ways to communicate in Messages, new ways to use Siri with your favorite apps, beautifully redesigned Maps, Photos, Apple Music and News, and the Home app, which lets you simply and securely set up, manage and control your home all in one place.
(RED)’s critical work provides access to life-saving HIV/AIDS programs in sub-Saharan Africa, which is home to more than two thirds of the world’s HIV-positive population. One hundred percent of all money raised by (RED) goes directly to Global Fund HIV/AIDS grants that provide testing, counseling, treatment and prevention programs with a specific focus on eliminating transmission of the virus from moms to their babies. Since it was founded in 2006, (RED) has generated more than $465 million for the Global Fund, with more than $130 million from Apple alone.
source : 

Hub vs Switch – Differences

Device Hub Switch
Layer Layer 1 device; Physical Layer Layer 2 device; Data link Layer
Device type Multiport repeater.

Pass all information received to all connected devices. It creates unnecessary traffic.

Network device.

Pass information only those devices need it. It avoids unnecessary traffic.

Network Use for smaller network Use for larger network
Function Connect a network, computers join in central hub Join multiple computers together within one local area network (LAN).
VLAN There is no VLAN function. VLAN can be created and security can be applied.
Broadcast One. One broadcast domain.

By default, do not breakup broadcast domain.

Forwarding Broadcast all connected devices. By default, do not forward packets to other networks like routers.
Bandwidth Provides less bandwidth. Provides more bandwidth.
Collision domain One.

Collision occurs commonly.



No collision occurs in full duplex switch.

Spanning Tree No Many
Duplex Half duplex Half / Full duplex
Ports Up to 12 ports Up to 48 ports
Speed Up to 10 Mbps Up to 10 Gbps


  • Layer 2 device; Data link Layer
  • Allow to connect multiple devices and port can be manged. Vlan can create & security can be apply.
  • Do not breakup broadcast domain by default
  • Do not forward packets to other networks like routers
  • Providing more bandwidth for LAN users
  • Only ‘Switch’ frames from one port to another within the switched network
  • Use hardware address to filter a network
  • Many collision domain
  • One broadcast domain


  • Layer 1 device; Physical Layer
  • To connect network, join through central hub
  • 1 Collision domain
  • 1 broadcast domain
  • Never full duplex
  • Multi-port repeater