Data Recovery Over Hard Disk Failure

Hard Disk: An Introduction

Hard Disks are used to store information. All information on computers are stored in files. Hard disks store the majority of information on today's modern computer. Hard disk drives (HDDs) can be critically damaged by static electricity, shock, and other factors, often resulting in failure or the loss of valuable data. In many cases it may become necessary to recover information from your hard drive. Such retrieval is quite possible.

Hard Disk Failure

*Physical Failures

Physical failure occurs from sudden switch off, power failure, sliding them off desks and cheap components. As for data loss, data is only magnetic impulses on the surface of a hard disk. And ridiculously small bits of magnetism at that! When the magnetic impulse fades, or changes position, trouble starts.

Drive Alignment Drift is another cause of problems. Mechanical devices are subject to wear and tear, heat and cold, loosening tolerances etc.

The small changes in the read/write heads wouldn't matter usually, as data still gets written in the same place as it will be read later. However, there is some data that hardly ever gets re-written, and that is the Sector ID Headers.

*Logical Failures

Master Boot Record Failure

Technically, when the Master Boot Record is working correctly, the master boot code scans the partition table for the active partition, finds the starting sector, loads a copy of the boot sector from the active partition into memory and then transfers control to the executable code in the boot sector. If the master boot code cannot complete these functions, the system displays a message similar to the MBR error.

*Boot Sector Failure

The boot sector is a region of a hard disk, floppy disk, and other similar data storage device. It is loaded to memory and executed as a part of the bootstrap sequence. The boot sector contains a small computer program that is loaded on the operating system into memory and transfers the control.

Most boot sector failure occurs by the defection of boot sector virus. Boot sector viruses are usually spread by infected floppy disks. In the past, these were usually bootable disks, but this is no longer the case. A floppy disk does not need to be bootable to transmit a boot virus. Any disk can cause infection if it is in the drive when the computer boots up or shuts down.

*Accidentally Deleted Data

Some time some how you may delete a file thinking we don?t need it any more, but in a week or or two you may realize that it is a needed one. It happens to the best of us, but fortunately there are ways to get these lost files back.

When it comes to data on your computer, it is almost impossible to accidentally remove it beyond recoverability. Even if you are intentionally trying to completely wipe a file from your hard drive it is exceedingly difficult.

*Cross Linked Files

A file system error that corrupts the contents of an existing file by writing data from another file into the same cluster. Running Scandisk or a similar program cleans up the problem, but one of the files is no longer usable.

*Bad Sectors

It is a portion of the Hard disk that cannot be used any more. If a part of the disk get bad sector which contains data then those data is to be recovered before use. When you format a disk, the OS will mark all the unusable sector as bad sector, however, this does not affect the overall performance of the disk as the damaged space is considered unusable.

Hard Disk Data Recovery

*Replace the (Circuit Board) PCB

Upon a Hard Drive circuit board failure, it is possible to get back the data by carefully replacing the PCB of the hard drive.

*Replace the Firmware

Hard disk firmware is the information that is used by the computer that allows it to correctly interact with the hard disk. It may be replaced or updated by the matching firmware.

*Replace the Head Stack

There are common situation that may be due to head failures. There is a small chip located in the head stack that is called PREAMPLIFIER. Working with preamplifiers always includes some difficulties, because, practically, they can not withstand static discharges. If re-soldering is needed, one should follow a number of rules to protect a preamplifier from static damage caused by careless finger touching. Although this task is very risky and it should be done in a high secured lab specially created for this task.

*Move the disk to another Drive

In some cases complete functionality of the Hard drive may be disabled while only the internal disk plate is without any damages or errors. In those situations, it is possible to move the disk to another drive.

*Spin-Stand Testers

Hard drive manufactures and their head media; preamplifier and read channel suppliers do have very accurate, very expensive "magic machines" called Spin-Stands. These are used for testing and experimenting with heads and disks. They are used mostly by researcher and development departments.

*Magnetic Force Microscopes (MFM)

Magnetic force microscopy is a powerful tool for high-resolution magnetic imaging of most data storage media. As the density of magnetic media is higher, the bit becomes smaller than the wavelength of light, so optical techniques can not resolve it. General MFM is capable of imaging the magnetic domain of several tens of nanometers. Also, MFM is almost simultaneous with measuring the surface characteristics of topography and roughness of the same area with sub-angstrom vertical resolution.

Recovery Softwares

*SpinRite 6.0

SpinRite is a stand-alone DOS program designed to refurbish hard drives, floppy disks and recover data from marginally or completely unreadable hard drives and floppy disks and from partitions and folders which have become unreadable.

*Ontrack data recovery software

Ontrack Data Recovery offers the industry's highest quality and cost-effective do-it-yourself data recovery software solutions for almost any data loss situation covering servers, desktops or laptops for all media, operating systems and file types. Ontrack's EasyRecoveryTM family of products is unmatched in its ability to recover/repair from all causes of lost data.

*Recover My Files

Recover My Files data recovery software will easily recover deleted files emptied from the Windows Recycle Bin, or lost due to the format or corruption of a hard drive, virus or Trojan infection, and unexpected system shutdown or software failure.

For more Data recovery topics http://www.pc4safe.com

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Speeding PHP Using APC PHP Cache

If you look at a PHP source file you will notice one thing. It's a source file. Not particularly surprising, but think about when you deploy a PHP application, what do you deploy? PHP source files. Now for many other languages; Java, C, etc when you deploy an application you deploy the compiled file. So, the question that you want to ask yourself is this, how much time does a PHP application spend compiling source files vs running the code? I'll answer that for you, a lot.

There are advantages to being able to deploy source files though. It makes it easy to do on the fly modifications or bug fixes to a program, much like we used to do in the early BASIC languages. Just change the file and the next time it's accessed your change is reflected. So, how do we keep the dynamic nature of PHP, but not recompile our files every time they are accessed?

A PHP cache. It's surprising to me that this concept isn't built into the base PHP engine, but perhaps that's because some company's can sell this add on to speed up PHP. Luckily for us, some companies/open source projects provide this plug in to PHP at no charge. These plug ins are generally known as PHP accelerators, some of them do some optimization and then caching and some only do caching. I'm not going to pass judgement on which one is the best, any of them are better than nothing, but I decided to use APC, the Alternative PHP Cache. I chose this one because it is still in active development and is open source and free.

Alternative php cache can be found at php.net, just look down the left column for APC. It comes in source form, so you will need to compile it before installing it, don't worry about that part. If you're using Red Hat 4 or CentOS4 I'll tell you exactly how to do it. If you're using something else, you'll need the same tools, but getting the tools might be a bit different.

1. The Tools

Do you know how many web sites, forums and blogs I went to with my error messages before I found the answers as to what I was missing when I was trying to install APC - Alternative PHP Cache? Two days worth, but I finally found the correct combination and it's really quite obvious as is everything once you know the answer. There are three sets of dev tools that you will need.

1a. You'll need a package called "Development Tools" this will include all the important dev tools like the GCC compiler, etc.

1b. You'll need a package called php-devel which as you might guess are development tools for PHP

1c. You'll need a package called httpd-devel which of course are dev tools for Apache web server.

On Red Hat or CentOS getting these should be as easy as the following 3 commands:

yum groupinstall "Development Tools"

yum install php-devel

yum install httpd-devel

You'll do these three one at a time and follow any instructions (usually just saying yes).

Now it's time to follow the instructions contained in the APC package. Since these may change over time I'm not going to go through them. They are very complete. If you follow the instructions and get an apc.so file out of it, then you're all set, just modify your php.ini file and you're good to go.

There are two problems that I encountered that you may encounter too. The first is an error when running phpize. I ignored this error and everything succeeded okay, but not before I spent hours looking for the solution to this error. Here is the error.
configure.in:9: warning: underquoted definition of PHP_WITH_PHP_CONFIG

run info '(automake)Extending aclocal'

or see http://sources.redhat.com/automake/automake.html#Extending-aclocal

configure.in:32: warning: underquoted definition of PHP_EXT_BUILDDIR

configure.in:33: warning: underquoted definition of PHP_EXT_DIR

configure.in:34: warning: underquoted definition of PHP_EXT_SRCDIR

configure.in:35: warning: underquoted definition of PHP_ALWAYS_SHARED

acinclude.m4:19: warning: underquoted definition of PHP_PROG_RE2C

People would have had me updating my PHP version from 4.3.9 and everything else under the sun to get rid of this error, but in the end it didn't matter. My APC compiled and installed nicely and I am good to go.

The other slight problem that I ran into was the location of php-config. The install instructions wanted me to do the following:

./configure --enable-apc-mmap --with-apxs
--with-php-config=/usr/local/php/bin/php-config

However my php-config is in /usr/bin/php-config. Making that change allowed this part to work.

So, have at it, once it's done you can expect to see huge improvements in your web site response times and reductions on your CPU load. One more quick note, My server hosts about 20 web sites, but only 3 or 4 are really busy. To reduce the memory footprint of caching everything for all 20 sites I used the apc.filters property. Although this property is slightly flawed for non qualified includes, it worked nicely for my Serendipity blogs. Your mileage with this property will vary according to the software you are using and how it does it's includes.

Jon runs UFC fan site UFC Results come to UFC Results at http://www.ufcresultslive.com for UFC Results, Predictions, News and of course Fighter Rankings.

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