open source

Wednesday, November 9, 2011

Lifeline
Lifeline Communiqué
Communiqué
Date: 09th Nov 2011
Tip of the Day:

Hardware Vs Software RAID
Feature
Software RAID Hardware RAID
Cost: High
Low
Software RAID is part of OS, so no need to spend extract money.
Complexity: Low
The software RAID works on partition level and it can sometime
Medium to high
increase complexity if you mix different partitions and hardware
RAID.
Write back caching (BBU): Yes
The software RAID cannot add a battery. Hardware RAID can
run in write-back mode if it has a BBU installed. With BBU
pending writes are not lost on a power failure.
No
Performance: High
With the software based RAID0 and RAID1 performance is
negligible. However, performance goes down when you use
Depend upon
parity-based arrays and/or several arrays at the same time. The
usage
performance of a software-based array is dependent on the server
CPU performance and current load.
Overheads (CPU, RAM etc): No
The software RAID must use server's CPU and RAM for RAID
Depend upon
software. The more hard drives means more CPU cycle will go to
usage
software RAID instead of your Apache / Postfix or MySQL
server.
Disk hot swapping: Yes
It means replacing hard disk without shutting down the server.
Many RAID controller supports disk hot swapping.
No
Regards, Team TSG, Infrastructure Availability
Services
Hot spare support: Yes
A hard disk is physically installed in the array which stays
inactive until an active drive fails, when the system automatically Yes
replaces the failed drive with the spare, rebuilding the array with
the spare hard disk included.
/boot partition: No Yes
It is hard to make fail over with software RAID if /boot fails
while booting the server. This can result into unexpected errors
and data loss. However, LILO and FreeBSD loader can get
around this problem too.
Open source factor: No
*BSD / OpenSolaris and Linux RAID software drivers are open
source. It means more people can fix problems as compare to a Yes
closed source hardware firmware. You can move, mix and match
different sizes with open source software RAID.
Vendor lock in (open formats): See above. No Yes
Higher write throughput: No Yes
Hardware RAID with BBU may offers higher write throughput.
Faster rebuilds: Yes
Hardware RAID with BBU may offers faster rebuilds as compare No
to software based solution.
Can act as a backup solution?: No No
Both software and hardware RAID cannot protect you against
human errors or system failures or viruses. Daily scheduled and
off site backups of your system are highly recommended. Use
tools such as rsync, rsnapshot, tar, dump, restore and others to
make daily backups.
Recommend usage: +Low cost +Do you run a
                 solution mission critical
                 +Better for cluster or setup?
                 RAID0 or +Heavy database
                 RAID1 driven dynamic
                 +Single server / site
                 workstation +Do you want the
                 +Perfect for highest
                 home and small performance
                 business users. possible?
                 +No vendor lock-
                 ins
Regards, Team TSG, Infrastructure Availability
Services

Tuesday, November 8, 2011

Sunday, November 6, 2011

Browser Statistics

Browser Statistics Month by Month

2011	Internet Explorer	Firefox	Chrome	Safari	Opera
September	22.9 %	39.7 %	30.5 %	4.0 %	2.2 %
August	22.4 %	40.6 %	30.3 %	3.8 %	2.3 %
July	22.0 %	42.0 %	29.4 %	3.6 %	2.4 %
June	23.2 %	42.2 %	27.9 %	3.7 %	2.4 %
May	24.9 %	42.4 %	25.9 %	4.0 %	2.4 %
April	24.3 %	42.9 %	25.6 %	4.1 %	2.6 %
March	25.8 %	42.2 %	25.0 %	4.0 %	2.5 %
February	26.5 %	42.4 %	24.1 %	4.1 %	2.5 %
January	26.6 %	42.8 %	23.8 %	4.0 %	2.5 %

Friday, November 4, 2011

PHP String Variables

A string variable is used to store and manipulate text.

String Variables in PHP

String variables are used for values that contain characters.
In this chapter we are going to look at the most common functions and operators used to manipulate strings in PHP.
After we create a string we can manipulate it. A string can be used directly in a function or it can be stored in a variable.
Below, the PHP script assigns the text "Hello World" to a string variable called $txt:

<?php
$txt="Hello World";
echo $txt;
?>

The output of the code above will be:

Hello World

Now, lets try to use some different functions and operators to manipulate the string.

The Concatenation Operator

There is only one string operator in PHP.
The concatenation operator (.) is used to put two string values together.
To concatenate two string variables together, use the concatenation operator:

<?php
$txt1="Hello World!";
$txt2="What a nice day!";
echo $txt1 . " " . $txt2;
?>

The output of the code above will be:

Hello World! What a nice day!

If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string (a space character), to separate the two strings.

The strlen() function

The strlen() function is used to return the length of a string.
Let's find the length of a string:

<?php
echo strlen("Hello world!");
?>

The output of the code above will be:

The length of a string is often used in loops or other functions, when it is important to know when the string ends. (i.e. in a loop, we would want to stop the loop after the last character in the string).

The strpos() function

The strpos() function is used to search for a character/text within a string.
If a match is found, this function will return the character position of the first match. If no match is found, it will return FALSE.
Let's see if we can find the string "world" in our string:

<?php
echo strpos("Hello world!","world");
?>

The output of the code above will be:

The position of the string "world" in the example above is 6. The reason that it is 6 (and not 7), is that the first character position in the string is 0, and not 1.

PHP String Variables

A string variable is used to store and manipulate text.

String Variables in PHP

<?php
$txt="Hello World";
echo $txt;
?>

The output of the code above will be:

Hello World

Now, lets try to use some different functions and operators to manipulate the string.

The Concatenation Operator

There is only one string operator in PHP.
The concatenation operator (.) is used to put two string values together.
To concatenate two string variables together, use the concatenation operator:

<?php
$txt1="Hello World!";
$txt2="What a nice day!";
echo $txt1 . " " . $txt2;
?>

The output of the code above will be:

Hello World! What a nice day!

If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string (a space character), to separate the two strings.

The strlen() function

The strlen() function is used to return the length of a string.
Let's find the length of a string:

<?php
echo strlen("Hello world!");
?>

The output of the code above will be:

The strpos() function

<?php
echo strpos("Hello world!","world");
?>

The output of the code above will be:

The position of the string "world" in the example above is 6. The reason that it is 6 (and not 7), is that the first character position in the string is 0, and not 1.

PHP Variables

A variable is used to store information.

Variables in PHP

Variables are used for storing values, like text strings, numbers or arrays.
When a variable is declared, it can be used over and over again in your script.
All variables in PHP start with a $ sign symbol.
The correct way of declaring a variable in PHP:

$var_name = value;

New PHP programmers often forget the $ sign at the beginning of the variable. In that case it will not work.
Let's try creating a variable containing a string, and a variable containing a number:

<?php
$txt="Hello World!";
$x=16;
?>

PHP is a Loosely Typed Language

In PHP, a variable does not need to be declared before adding a value to it.
In the example above, you see that you do not have to tell PHP which data type the variable is.
PHP automatically converts the variable to the correct data type, depending on its value.
In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.
In PHP, the variable is declared automatically when you use it.

Naming Rules for Variables

A variable name must start with a letter or an underscore "_"
A variable name can only contain alpha-numeric characters and underscores (a-z, A-Z, 0-9, and _ )
A variable name should not contain spaces. If a variable name is more than one word, it should be separated with an underscore ($my_string), or with capitalization ($myString)

PHP Syntax

Basic PHP Syntax

A PHP scripting block always starts with <?php and ends with ?>. A PHP scripting block can be placed anywhere in the document.
On servers with shorthand support enabled you can start a scripting block with <? and end with ?>.
For maximum compatibility, we recommend that you use the standard form (<?php) rather than the shorthand form.

<?php
?>

A PHP file normally contains HTML tags, just like an HTML file, and some PHP scripting code.
Below, we have an example of a simple PHP script which sends the text "Hello World" to the browser:

Each code line in PHP must end with a semicolon. The semicolon is a separator and is used to distinguish one set of instructions from another.
There are two basic statements to output text with PHP: echo and print. In the example above we have used the echo statement to output the text "Hello World".
Note: The file must have a .php extension. If the file has a .html extension, the PHP code will not be executed.

Comments in PHP

In PHP, we use // to make a single-line comment or /* and */ to make a large comment block.