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Written by Elena Pakhomova of www.ReclaiMe.com, specializing in data recovery solutions for storage devices.
When you need to erase data irreversibly
You don't want that someone inspects your data
There are situations when you need to erase data from a data storage device irreversibly. For example, you want to give away or sell your hard disk. Obviously, you don't want someone else inspecting your data. In such cases it is not enough to just delete all folders and files because any data recovery software can easily restore all the data back.
To be sure that all the data is deleted irreversibly you can:
• first delete all old data, then write some useless data to fill the entire disk; movies, cartoons are ideal for this. Finally, you should check that the disk space is filled with new data.
• use complete format when formatting the device in Windows Vista/7. Actually, there is no a “complete format” button; to do a complete format you need to uncheck a “perform a quick format” checkbox. Note that if you apply a complete format under Windows XP, the data is still recoverable.
• take a special tool which is capable of erasing data from storage devices irreversibly. Sometimes such tools are also called low level format tools.
The third method is the most convenient and easy. You just download software to erase data, select a device, and start erasing. There are many tools to erase data off a drive irreversibly, both paid and free, for example Lowvel and HDD LLF.
Freshen up a second hand hard drive
When you are going to use a second hand disk, it is desirable that you do the low level format (zero fill) using special software before writing your own data on it. The point is that such tools write to each sector on the disk. Usually the tools write all zeros or all binary 1s, although there is no standard what to write and, frankly speaking, from the users' point of view it doesn't matter what “rubbish” will fill his or her disk.
When the tools write to each sector on the disk they help to detect bad sectors, forcing the disk to reallocate them, i.e. to replace bad sectors with “healthy” ones from a reserved pool.
When a low level format tool completes the format, you can look into the S.M.A.R.T. data and find out, say, that there are too many bad sectors on the disk and therefore it makes no sense to keep it. Alternatively, you can see that the disk is OK and it is safe to store your data on it. In S.M.A.R.T. data the value of 197 attribute (Current Pending Sector Count) must be zero. If you cannot achieve zero in this attribute even after several zero-fill runs, it would be better to replace the disk.
All in all, erasing of the disk with a low level format tool allows you to avoid some of the problems relating to data loss due to a disk failure in the future.
Improve performance on SSD
Solid State Drives (SSD) may or may not support a TRIM command forcing an SSD to erase unused data blocks in advance (old SSDs typically don't). Additionally, it is often impossible to use TRIM on SSDs connected to RAID controllers.
Using TRIM improves SSD performance in terms of write speed because an SSD can write only to a blank block, that was never written to or that is already erased. If a block is not erased, then new data cannot be written to it until the block is erased.
If SSD does not support TRIM, its write speed will degrade since it will need to erase a block before to write user data. If there is a possibility, you should do low level format for such SSDs from time to time. Notable difference from the previous cases is that a low level format tool which is used to erase an SSD must fill the disk with zeros, not with something else.
It is interesting to note that zero filling can be applied not only to an SSD not capable of TRIM, but also to a TRIM-capable SSD working under an operating system that doesn't support TRIM, like Windows XP.
How to erase data irreversibly using low level format software
1. Download and install low level format software. Take care not to install the software on a drive which you are going to “kill”.
2. Launch the software, specify the disk to erase.
3. Click the “Start” button. On this step you get the full information about the drive: model name, revision, names and sizes of the partitions it contains, filesystems used on the partitions and so on. Along with the information, you get a warning saying the data on the drive will be erased irreversibly. At this point you still can cancel data erasing by clicking the “Cancel” button.
4. Click “Erase”. The software will begin to overwrite the drive's contents with zeros, showing the process of erasing on the disk map in real time.
Once the tool completes its work, the drive's contents will be overwritten and no one, not even the FBI, can restore the previous data.