Wednesday, April 27, 2011

Features of good data recovery software

I am sometimes asked what qualities or features I consider to be important when choosing data recovery software to recommend. So here is a list of the things I look for.
  • A well designed user interface. Do it yourself data recovery software is often used by people with little computer knowledge. If it is not easy to use, it will not be any use to them; it may even do more harm than good.
  • Developed by a company with a track record in data recovery. It takes time and continuous effort to develop and refine software to create one of the best data recovery utilities. Data recovery is a lucrative market segment and many new software companies are jumping on the bandwagon. There are also cheap or free products that may be capable of some basic undelete tasks but fail in cases where the data is still recoverable.
  • Support for many different file types. The hallmark of a professionally developed data recovery software is that it can detect and piece together files of many different types, even where other clues to their location have vanished. The Power Search Technology in Uneraser and other Diskinternals data recovery tools can detect more than 160 different file types.
  • Searching and filtering. An effective data recovery software will recover thousands of potential deleted and lost files, many of which will be files you are not interested in. Searching and filtering functions will save hours of looking through recovered files and help you find the ones you want quickly.
  •  Comprehensive file preview. Many data recovery products only have a basic viewer for recovered files that typically can display only popular image file types, showing everything else as raw text data. This is useless when trying to recover other types of file such as Microsoft Office documents. Together with search and filter functionality, a good previewer can save a great deal of time when trying to recover lost files.
  • Run without installation. It is very helpful to be able to run the data recovery program without it having to be installed in the Registry of the computer it is run on. Although the DiskInternals products use an installer for convenience, they can be installed on to a USB drive or copied to CD and then run on another computer.
  • Try before you buy. Unfortunately, not all lost files are recoverable. No-one wants to spend a lot of money only to find that their data cannot be recovered, so it is essential that a do it yourself data recovery product can be run in trial mode so that you can see whether it is able to find your files.

Thursday, December 16, 2010

Recovering deleted photos

One of the most common data recovery tasks is to restore lost photos. Often, the photos were lost when they were accidentally deleted. But it is all too easy to corrupt a digital camera memory card, perhaps by disconnecting it from the computer before all read, write or delete operations have been completed. This can corrupt the file system and make the memory card unreadable. To restore use of the memory card it is usually necessary to format it, which effectively deletes the photos that were on it.

As in the case when files are deleted, formatting a memory card does not physically delete the existing data, so the lost photos are still recoverable. Memory cards look to the computer just like a removable disk drive, so lost files may be recovered using general deleted files recovery software like Uneraser. But you may also use specialist photo recovery software.

Photo recovery software is usually a bit cheaper to buy, because it does not need to include the capability to identify and recover non-image files. Two good photo recovery software packages that recommends are Photo Recovery and Flash Recovery.

Wednesday, December 1, 2010

If Windows Won't Boot

One of the most panic-inducing moments you can have with a computer is when you switch it on and Windows fails to boot. There are many possible causes of this, ranging from hard drive controller failure (rare, but not fixable using software) to corruption of Windows system files (usually resulting in some blue screen error message) which have many different solutions.

If you see a message right at the start of the boot-up process on the lines of "No system disk" then disconnect any external hard drives and USB sticks and make sure the CD/DVD drive is empty as the computer may be trying to boot from something other than the hard disk. If that doesn't help, restart and press the key (usually the Del key or one of the F keys) to get into the BIOS settings and check that the boot sequence includes the hard drive - the settings might have got corrupted.

If you're sure that the PC is trying to boot from the hard drive then a common reason for failure is corruption of the partition table. There is rarely any need to use data recovery software in this case. All you need to do is fix the partition table and your files will reappear as if by magic. A good and easy to use tool that can do this for you is the Partition Table Doctor Boot CD.

The Partition Table Doctor Boot CD is available online as an .ISO CD image that you can download and burn to CD using any CD image burning program. After you have done that, boot the PC from this CD. In most cases, Partition Table Doctor will detect the problem automatically and guide you through the steps needed to fix it.

Friday, November 26, 2010

Dangers of Disk Housekeeping

Many computer users like to keep their hard drives tidy by cleaning up redundant files. This is actually a dangerous exercise. Let me explain.

When Windows saves a file to disk, it tries to find a single block of space large enough to store the file instead of fragmenting the data across blocks of space in different parts of the drive. Whether a file is fragmented or not makes no difference to being able to access the file. As long as the file appears in a folder listing, the file system holds the information to be able to link the different blocks together in the right order. But it is faster and more efficient to be able to read a file from one continuous block - though to be truthful, with modern fast PCs and hard drives the difference is hardly noticeable.

Some types of file can't easily be stored in a continuous block, either because they are very large and there isn't a single block of space big enough anywhere on the hard drive, or because the file grows over a period of time and other files have been created that prevent its original space from being extended. Database files and Microsoft Office documents are good examples of files that grow over a period of time.

Microsoft Windows has always included a Disk Defragmenter tool. Its purpose is to improve system performance by ensuring that files on the disk are not fragmented. Although running the defragmenter may not make much difference to the perceived performance of a modern PC, it does have an effect - both good and bad - on the chances of recovering deleted files, and that is what we should be concerned about.

When a file is first deleted, its directory entry and related file system information aren't immediately deleted or overwritten so the file may be recovered intact even if it was fragmented. After these file system structures have been overwritten by new data, however, the only way a file may be recovered is forensically. Essentially what happens then is that the recovery software scans the hard drive examining it block by block. Most files start off with a "header block" that identifies the type of file and contains other information such as the length of the file. When a header block is detected, the recovery software must assume - in the absence of other information from the file system - that the file was not fragmented, and that the file consists of that header block plus however many consecutive data blocks are needed to contain the length of file stated in the header.

It follows from this that the chances of recovering a deleted file, even if it was deleted a long time ago, are much greater if the file was not fragmented at the time it was deleted. At the same time, running Disk Defragmenter severely harms the chances of recovering files that were deleted prior to running it, as the disk space those deleted files occupied are likely to be reused to hold relocated data. The common quiet afternoon task of cleaning up the hard drive followed by emptying the Recycle Bin and defragmenting is actually one of the worst things you can do. Disk housekeeping is one of the most common causes of deleting wanted files and by emptying the Recycle Bin and defragmenting you have just made the job of recovering those deleted files much more difficult.

Tuesday, November 23, 2010

File systems

File system (sometimes written as filesystem) is the term used to describe the method used to store files on disk drives and other storage media. There are many different file systems in common use.
  • FAT (for file allocation table) is one of the oldest file systems and was originally designed for use with floppy disks under MS-DOS. It is supported by all major operating systems and many other devices. Extended to allow use with hard drives, it is now rarely used due to a low limit on the maximum size of an individual drive or partition and the fact that file names are limited to eight characters plus a three character extension.
  • FAT32 is a development of FAT that is able to support larger drives and partitions and file names of up to 255 characters in total length. Introduced with Windows 95, it is falling out of use in computers as it is inefficient when used with large hard drives, lacks any access control features and is prone to corruption. However it is commonly used with memory cards (such as in digital cameras) and removable drives due to its simplicity and it is supported by most major operating systems not just Windows.
  • NTFS (for New Technology File System) is so named as it was introduced with Windows NT, the forerunner of Windows XP, Vista and Windows 7. There are many versions of NTFS, each introducing new features. NTFS includes many features considered necessary to support a modern operating system including access rights and encryption. It is fully supported only under Windows though Mac OS and Linux support read access to allow NTFS partitions on a dual boot system to be read.
  • HFS (for Hierarchical File System) was developed by Apple for use on Mac OS. There is also a newer version able to support larger files called HFS Plus. It is an advanced file system offering many of the same capabilities as NTFS but is only supported on Mac OS.
  • ISO 9660 is an International Standards Organization file system which is used on CDs, DVDs and other optical media. It was designed to be independent of operating system and is supported by all major operating systems.
  • UDF (Universal Disk Format) is a file system that is mostly used on DVDs and other high capacity optical media where it is replacing ISO 9660.

If you need to recover deleted files from a non-optical storage device then use a data recovery program written for the type of computer (operating system) that can read the device. So a Windows program like Uneraser will be able to recover files from a drive written by Windows and a Mac program like File Recovery for Mac will be able to recover files from a drive written by a Mac.

The file systems used for optical storage media are not generally supported by hard drive data recovery software so to recover files from CD and DVD you must use a specialized program such as IsoBuster.

Monday, November 22, 2010

Bugged by the bin

Regularly emptying the Recycle Bin makes it an ineffective tool for recovering deleted files. In the days of Windows 95 when the Recycle Bin was introduced, hard drives were small and computers were slow and emptying the bin was necessary to avoid the system grinding to a halt whenever you deleted a file. But with today's fast PCs having drives with hundreds of gigabytes of storage space it isn't necessary, especially when weighed against the trouble caused by being unable to recover a deleted file.

Unfortunately that desktop icon showing a full Recycle Bin is a constant reminder that your computer still contains files you threw out, and some people have an instinctive desire to empty it. If you are being bugged by your full Recycle Bin, try this simple solution. Change the icon for the full bin so that it is the same as the empty one.

Right-click the desktop and select Personalize, then in the Control Panel Personalization window click on Change desktop icons. Select the Recycle Bin (full) icon, click Change Icon, select the empty bin icon and click OK. Now you won't be able to see that the Recycle Bin is full so you won't be as tempted to empty it.
  • To recover deleted files that are not in the Recycle Bin, use Uneraser

Thursday, November 18, 2010

How files are deleted

To understand how it is possible to recover deleted files it helps to know what happens when a file is deleted. I've mentioned the Recycle Bin already. It's a folder where files are moved to when you delete them from another folder so they can easily be recovered. But what happens to files when you empty the Recycle Bin, delete them from a removable drive, a memory card or a network drive, or use Shift+Delete to bypass the Recycle Bin?

Exactly what happens depends on the system used to organize files on your hard drive or other storage medium (the file system) but the details aren't really important. In essence, two things happen. A flag in the record for that file in the folder is changed to show it as deleted and the space on the drive that contained the data of the file is marked as available for re-use by the operating system. Although the file no longer appears in the folder and has gone as far as the operating system is concerned, the data has not been erased and the file is still fully recoverable.

If you act immediately you realize your mistake using a deleted files recovery software like Uneraser, you have a 100% chance of recovering that deleted file. This is the easiest task for recovery software. The file's record is still present in the folder containing all the details of the file including it's name, type, size, date created and date modified and the location of the file's data. All the recovery software has to do is clear the deleted flag from the record, remove the space holding the data from the free disk space pool and your file is back where it was originally.

As time passes since the file was deleted, two things will happen. The record containing the details of the deleted file will be reused to store information about a new file. And the space that held the file data will start to be overwritten by other data. There is no way to predict how long that will take. When testing data recovery software I have been surprised at some of the long-forgotten files that have been recovered. But I have also found more recently deleted files that could not be recovered perfectly because some of the original data had been overwritten. It depends on things like the size of the hard drive relative to the space you are using, how much you use the computer, whether you create many big files and where on the hard drive the file you deleted was stored.

To have the best chance of recovering deleted files, act as quickly as possible. Ideally you should stop using the computer and either take the hard drive out and attach it to another PC to run the data recovery or you should use bootable recovery media. We will look at these options in future postings.