Definition of:RAID (Redundant Array of Independent Disks)

A disk subsystem that increases performance or provides fault tolerance or both. RAID uses two or more regular hard drives and a RAID controller, which is plugged into motherboards that do not have RAID circuits. Today, most motherboards have built-in RAID but not necessarily every RAID configuration (see below). In the past, RAID has also been accomplished by software only but was much slower. In the late 1980s, the "I" in RAID stood for "inexpensive" but was later changed to "independent."

In large storage area networks (SANs), floor-standing RAID units are common with terabytes of storage and huge amounts of cache memory. RAID is also used in desktop computers by gamers for speed and by business users for reliability. Following are the various RAID configurations.

RAID 0

A popular disk subsystem that increases performance by interleaving data across two or more drives. Data are broken into blocks, called "stripes," and alternately written to two or more drives simultaneously to increase speed. For example, stripe 1 is written to drive 1 at the same time stripe 2 is written to drive 2. Then stripes 3 and 4 are written to drives 1 and 2 simultaneously and so on. When reading, stripes 1 and 2 are read simultaneously; then stripes 3 and 4 and so on.

 Ironically, RAID 0 is a misnomer because there is nothing "redundant." If one drive fails, the entire RAID array fails.

Disk Striping for Performance

Widely used for gaming, disk striping interleaves data across multiple drives for performance. However, there are no safeguards against failure.

RAID 0 Probability of Failure
The more drives in a RAID 0 array, the higher the probability of array failure. For example, if experience tells us that one out of a thousand drives fails in a year, the probability that a 2-drive array will fail in a year is 1 in 500; that a 3-drive array will fail is 1 in 333 and so on.

The formula: if the probability of failure of each of n drives is p for a given period, then the probability of not failing is (1-p). The probability of all drives functioning is (1-p)^n, and the probability that at least one drive will fail, causing the array to fail, is [1-(1-p)^n].

RAID 1

A popular disk subsystem that increases safety by writing the same data on two drives. Called "mirroring," RAID 1 does not increase performance. However, if one drive fails, the second drive is used, and the failed drive is manually replaced. After replacement, the RAID controller duplicates the contents of the working drive onto the new one.

Mirroring for Fault Tolerance

Widely used, mirroring writes two drives at the same time so that data are duplicated. It provides the highest reliability, but doubles the number of drives needed.

RAID 1 Probability of Failure
The more drives in a RAID 1 array, the lower the probability of failure. For example, if experience tells us that one out of a thousand drives fails in a year, the probability that an entire 2-drive array will fail in a year is 1 in a million; that an entire 3-drive array will fail is 1 in a billion and so on.

The formula: if the probability of failure of each of n drives is p, then the probability that all the drives will fail is p^n.

RAID 3

A disk subsystem that increases safety by computing parity data and increasing speed by interleaving data across two or more drives (striping). RAID 3 achieves the highest data transfer rate because all drives operate in parallel. Using byte level striping, parity bits are stored on separate, dedicated drives. Somewhat similar, RAID 4 uses block level striping but is not as popular.

RAID 3 - Speed and Fault Tolerance

With data striped across two or more drives, RAID 3 achieves the highest data transfer rate because all drives operate in parallel.

RAID 5

A popular disk subsystem that increases safety by computing parity data and increasing speed by interleaving data across three or more drives (striping). RAID 5 is similar to RAID 3, except that RAID 5 parity is distributed among all drives, whereas RAID 3 uses separate parity drives.

RAID 6
Similar to RAID 5 but not as widely used, RAID 6 performs either two parity computations instead of one, or it performs the same parity computation on overlapping subsets of the data. Using four drives, RAID 6 can recover from two failed disks.

RAID 5 - Speed and Fault Tolerance

With data and parity striped across three or more drives, RAID 5 has been a popular method for obtaining speed and safety.

RAID 10

 

A RAID subsystem that increases safety by writing the same data on two drives (mirroring), while increasing speed by interleaving data across two or more mirrored "virtual" drives (striping). RAID 10 provides the most security and speed but uses more drives than the more common RAID 5 method. S

RAID 10 Architectures

With RAID 1+0, the drives are set up as mirrored pairs and then striped. In this configuration, a drive in each mirrored pair can fail. In RAID 0+1, they are striped first, and then mirrored. If a drive fails in one of the stripe sets, then the other stripe set must be used, and no drive can fail in that set.

Thanks PCM

Mobile phone shows 3G, H, H+, E and G

• G stands for GPRS and is the slowest standard, used is the GSM network (2G).
• E is an extension of GPRS, it is called EDGE and it is correspondingly a little faster, but still uses the old GSM network (2G).
• 3G stands for UMTS and is the successor to the GSM network and faster.
• H and H+ are standing for HSPA and HSPA+. Both use the UMTS network, where H is faster than 3G and H+ is faster than H.
• 4G stands for LTE and is the fastest.

USB Drive Folders Not Showing..............!

Click Start>Run> type cmd and press Enter.

Enter this command in commend prompt

                  attrib -h -r -s /s /d g:\*.*          ("g" is flash drive)

Wait little time, then check your flash drive.

Enabling Windows Firewall on Domain Controllers……!

You can enable Windows Firewall on your domain controllers for enhanced security, but you should add below mention exceptions. Otherwise client machine not able to join to your domain.

     

          Enable the File And Print Sharing exception.

          Enable program exceptions for lsass.exe

          Enable program exceptions for ntfrs.exe

(which are found under %windir%\system32)

          Enable below mention ports       

                53 (TCP and UDP)

                88 (TCP and UDP)

               123 (UDP), 135 (TCP)

              137 (TCP), 389 (UDP)

              464 (TCP and UDP)

              636 (TCP).

Deference Between HDD and SSD

Attribute	SSD (Solid State Drive)	HDD (Hard Disk Drive)
Power Draw / Battery Life	Less power draw, averages 2 – 3 watts, resulting in 30+ minute battery boost	More power draw, averages 6 – 7 watts and therefore uses more battery
Cost	Expensive, $1.00 per gigabyte (based on buying a 240GB drive)	Only around $0.075 per gigabyte, very cheap (buying a 4TB model)
Capacity	Typically not larger than 512GB for notebook size drives	Typically 500GB – 2TB for notebook size drives
Operating System Boot Time	Around 22 seconds average bootup time	Around 40 seconds average bootup time
Noise	There are no moving parts and as such no sound	Audible clicks and spinning can be heard
Vibration	No vibration as there are no moving parts	The spinning of the platters can sometimes result in vibration
Heat Produced	Lower power draw and no moving parts so little heat is produced	HDD doesn’t produce much heat, but it will have a measurable amount more heat than an SSD due to moving parts and higher power draw
Failure Rate	Mean time between failure rate of 2.0 million hours	Mean time between failure rate of 1.5 million hours
File Copy / Write Speed	Generally above 200 MB/s and up to 500 MB/s for cutting edge drives	The range can be anywhere from 50 – 120MB / s
Encryption	Full Disk Encryption (FDE) Supported on some models	Full Disk Encryption (FDE) Supported on some models
File Opening Speed	Up to 30% faster than HDD	Slower than SSD
Magnetism Affected?	An SSD is safe from any effects of magnetism	Magnets can erase data

How to Create Shutdown, Restart, Hibernate and Sleep Shortcuts for MS Windows

Right-click on the desktop, choose New and then Shortcut. In the shortcut location box, you will need to enter the correct command, which I have mention for you below. ( For Windows 7 & Windows 8)

Shutdown Computer           Shutdown.exe -s -t 00

       

Restart Computer              Shutdown.exe -r -t 00      

Lock Workstation              Rundll32.exe User32.dll,LockWorkStation

Hibernate Computer          rundll32.exe PowrProf.dll,SetSuspendState

Sleep Computer                 rundll32.exe powrprof.dll,SetSuspendState 0,1,0

                                              -f Forces running applications to close without warning.
                                                           -t xx Set timeout for shutdown to xx seconds.  

Windwos Shortcuts

Keyboard Shortcuts for (Microsoft Windows) :

1. CTRL+C (Copy)
2. CTRL+X (Cut)
3. CTRL+V (Paste)
4. CTRL+Z (Undo)
5. DELETE (Delete)
6. SHIFT+DELETE (Delete the selected item permanently without placing the item in the Recycle Bin)
7. CTRL while dragging an item (Copy the selected item)
8. CTRL+SHIFT while dragging an item (Create a shortcut to the selected item)
9. F2 key (Rename the selected item)
10. CTRL+RIGHT ARROW (Move the insertion point to the beginning of the next word)
11. CTRL+LEFT ARROW (Move the insertion point to the beginning of the previous word)
12. CTRL+DOWN ARROW (Move the insertion point to the beginning of the next paragraph)
13. CTRL+UP ARROW (Move the insertion point to the beginning of the previous paragraph)
14. CTRL+SHIFT with any of the arrow keys (Highlight a block of text) SHIFT with any of the arrow keys                     (Select more than one item in a window or on the desktop, or select text in a document)
15. CTRL+A (Select all)
16. F3 key (Search for a file or a folder)
17. ALT+ENTER (View the properties for the selected item)
18. ALT+F4 (Close the active item, or quit the active program)
19. ALT+ENTER (Display the properties of the selected object)
20. ALT+SPACEBAR (Open the shortcut menu for the active window)
21. CTRL+F4 (Close the active document in programs that enable you to have multiple documents open                             simultaneously)
22. ALT+TAB (Switch between the open items)
23. ALT+ESC (Cycle through items in the order that they had been opened)
24. F6 key (Cycle through the screen elements in a window or on the desktop)
25. F4 key (Display the Address bar list in My Computer or Windows Explorer)
26. SHIFT+F10 (Display the shortcut menu for the selected item)
27. ALT+SPACEBAR (Display the System menu for the active window)
28. CTRL+ESC (Display the Start menu)
29. ALT+Underlined letter in a menu name (Display the corresponding menu) Underlined letter in a command name on an open menu (Perform the corresponding command)
30. F10 key (Activate the menu bar in the active program)
31. RIGHT ARROW (Open the next menu to the right, or open a submenu)
32. LEFT ARROW (Open the next menu to the left, or close a submenu)
33. F5 key (Update the active window)
34. BACKSPACE (View the folder one level up in My Computer or Windows Explorer)
35. ESC (Cancel the current task)
36. SHIFT when you insert a CD-ROM into the CD-ROM drive (Prevent the CD-ROM from automatically playing)

Dialog Box - Keyboard Shortcuts :

1. CTRL+TAB (Move forward through the tabs)
2. CTRL+SHIFT+TAB (Move backward through the tabs)
3. TAB (Move forward through the options)
4. SHIFT+TAB (Move backward through the options)
5. ALT+Underlined letter (Perform the corresponding command or select the corresponding option)
6. ENTER (Perform the command for the active option or button)
7. SPACEBAR (Select or clear the check box if the active option is a check box)
8. Arrow keys (Select a button if the active option is a group of option buttons)
9. F1 key (Display Help)
10. F4 key (Display the items in the active list)
11. BACKSPACE (Open a folder one level up if a folder is selected in the Save As or Open dialog box)

Microsoft Natural Keyboard Shortcuts :

1. Windows Logo (Display or hide the Start menu)
2. Windows Logo+BREAK (Display the System Properties dialog box)
3. Windows Logo+D (Display the desktop)
4. Windows Logo+M (Minimize all of the windows)
5. Windows Logo+SHIFT+M (Restorethe minimized windows)
6. Windows Logo+E (Open My Computer)
7. Windows Logo+F (Search for a file or a folder)
8. CTRL+Windows Logo+F (Search for computers)
9. Windows Logo+F1 (Display Windows Help)
10. Windows Logo+ L (Lock the keyboard)
11. Windows Logo+R (Open the Run dialog box)
12. Windows Logo+U (Open Utility Manager)
13. Accessibility Keyboard Shortcuts
14. Right SHIFT for eight seconds (Switch FilterKeys either on or off)
15. Left ALT+left SHIFT+PRINT SCREEN (Switch High Contrast either on or off)
16. Left ALT+left SHIFT+NUM LOCK (Switch the MouseKeys either on or off)
17. SHIFT five times (Switch the StickyKeys either on or off)
18. NUM LOCK for five seconds (Switch the ToggleKeys either on or off)
19. Windows Logo +U (Open Utility Manager)
20. Windows Explorer Keyboard Shortcuts
21. END (Display the bottom of the active window)
22. HOME (Display the top of the active window)
23. NUM LOCK+Asterisk sign (*) (Display all of the subfolders that are under the selected folder)
24. NUM LOCK+Plus sign (+) (Display the contents of the selected folder)
25. NUM LOCK+Minus sign (-) (Collapse the selected folder)
26. LEFT ARROW (Collapse the current selection if it is expanded, or select the parent folder)
27. RIGHT ARROW (Display the current selection if it is collapsed, or select the first subfolder)

Shortcut Keys for Character Map : 

After you double-click a character on the grid of characters, you can move through the grid by using the keyboard shortcuts:

1. RIGHT ARROW (Move to the rightor to the beginning of the next line)
2. LEFT ARROW (Move to the left orto the end of the previous line)
3. UP ARROW (Move up one row)
4. DOWN ARROW (Move down one row)
5. PAGE UP (Move up one screen at a time)
6. PAGE DOWN (Move down one screen at a time)
7. HOME (Move to the beginning of the line)
8. END (Move to the end of the line)
9. CTRL+HOME (Move to the first character)
10. CTRL+END (Move to the last character)
11. SPACEBAR (Switch between Enlarged and Normal mode when a character is selected)

Main Window Keyboard Shortcuts : 

1. CTRL+O (Open a saved console)
2. CTRL+N (Open a new console)
3. CTRL+S (Save the open console)
4. CTRL+M (Add or remove a console item)
5. CTRL+W (Open a new window)
6. F5 key (Update the content of all console windows)
7. ALT+SPACEBAR (Display the MMC window menu)
8. ALT+F4 (Close the console)
9. ALT+A (Display the Action menu)
10. ALT+V (Display the View menu)
11. ALT+F (Display the File menu)
12. ALT+O (Display the Favorites menu)

MMC Console Window Keyboard Shortcuts :

1. CTRL+P (Print the current page or active pane)
2. ALT+Minus sign (-) (Display the window menu for the active console window)
3. SHIFT+F10 (Display the Action shortcut menu for the selected item)
4. F1 key (Open the Help topic, if any, for the selected item)
5. F5 key (Update the content of all console windows)
6. CTRL+F10 (Maximize the active console window)
7. CTRL+F5 (Restore the active console window)
8. ALT+ENTER (Display the Properties dialog box, if any, for the selected item)
9. F2 key (Rename the selected item)
10. CTRL+F4 (Close the active console window. When a console has only one console window, this shortcut closes the console)
Remote Desktop Connection Navigation
1. CTRL+ALT+END (Open the Microsoft Windows NT Security dialog box)
2. ALT+PAGE UP (Switch between programs from left to right)
3. ALT+PAGE DOWN (Switch between programs from right to left)
4. ALT+INSERT (Cycle through the programs in most recently used order)
5. ALT+HOME (Display the Start menu)
6. CTRL+ALT+BREAK (Switch the client computer between a window and a full screen)
7. ALT+DELETE (Display the Windows menu)
8. CTRL+ALT+Minus sign (-) (Place a snapshot of the active window in the client on the Terminal server clipboard and provide the same functionality as pressing PRINT SCREEN on a local computer.)
9. CTRL+ALT+Plus sign (+) (Place a snapshot of the entire client window area on the Terminal server clipboard and provide the same functionality as pressing ALT+PRINT SCREEN on a local computer.)

Microsoft Internet Explorer Keyboard Shortcuts :

1. CTRL+B (Open the Organize Favorites dialog box)
2. CTRL+E (Open the Search bar)
3. CTRL+F (Start the Find utility)
4. CTRL+H (Open the History bar)
5. CTRL+I (Open the Favorites bar)
6. CTRL+L (Open the Open dialog box)
7. CTRL+N (Start another instance of the browser with the same Web address)
8. CTRL+O (Open the Open dialog box,the same as CTRL+L)
9. CTRL+P (Open the Print dialog box)
10. CTRL+R (Update the current Web )

Keyboard Shorcuts for (Microsoft Windows) :

Keyboard Shorcuts for (Microsoft Windows) :