How DiskDeleter SSD wipe works

The popularity of SSD(Solid State Drive) PC is growing. As the number of SSD PCs in use has grown, so too has the need to sanitize SSD data. Returning or disposing a SSD PC without wiping its SSD could lead to data leakage. This must be prevented.

SSD is structured differently from HDD and wiping of SSD requires specialized knowhow, such as a software tool capable of wiping SSD. This page explains how HDD wipe and SSD wipe differ, and how DiskDeleter has overcome the difficulties in wiping SSD.

A major difference between HDD and SSDwiping

HDD Data Wipe

Some segments of HDD contain data. In this sample figure, colored segments contain data and white segments don’t.



When DiskDeleter wipes HDD, it overwrites the entire sections with numbers, like 0 or random numbers, according to the wipe method selected.



When wipe has completed, the entire sections contain no data.

SSD Data Wipe

SDD data wipe is more complex due to several built-in features specific to SSD or flash memory in general.

SSD characteristics compared with HDD

SSD is typically NAND Flash Memory, and neither does it have physical spinning disks nor movable read-write heads used in HDD. Thus, compared with HDD, SSDs are typically more resistant to physical shock, run silently, and have quicker access time and lower latency.

On the other hands, as SDD stores data in semiconductor cells, each of which can be put through a limited number of erase cycles before becoming unreliable. In order to work around this limitation, SSDs use “wear levelling” techniques in which data is arranged in a way that erasures and re-writes on memory cells are distributed evenly across all the blocks in the SSD medium. In this way, no single memory block prematurely fails due to a high concentration of write – erasure cycles. (The wear levelling is managed by controllers within SSD, which also manage its data mapping table.)

Ware levelling has significantly extended SSD’s product life. On the other hand, however, it has made simple data wipe impossible. Here is why.

SSD data erasure process

Due to the semiconductor wiring of SSD, data erasure can be done only by block.
In this sample diagram, one block consists of 4 cells, and the colored cells have data.



Now, if data in Red cells are to be erased, SSD must erase the blocks which contain Red data cells. Thus, it first copies the other data within a block which contains data to be erased.

     Original 1          
     Original 2  Original 3        
       Copy 1  Copy 4      
   Original 4  Copy 2  Copy 3        


Once the data are copied somewhere else, SSD then erases the entire blocks andother data in the erased blocks are retained somewhere else.

     Entire block is        
 Entire block is    Copy 1  Copy 4      
 erased    Copy 2  Copy 3        


This type of data relocation is constantly carried out by SSD controllers to effect ware leveling.  Data locations are recoded in data mapping tables stored within the controllers. This means when you instruct "write 0", it is not clear where the SSD controller will write "0". This in turn means that data erasure / wipe cannot be carried out independent of the ware levelling techniques implemented in each SSD.

SSD Secure Erase / Enhanced Secure Erase

As a part of the standardization of SSD specs, most SSDs have implemented [ Secure Erase ] command or [Enhanced Secure Erase ] command, which is effective in erasing data with its ware leveling implementation.

There are some common standard data wipe methods, like overwriting the data mapping table so that data cannot be read even if fragments of data remain on SSD. Some [ Enhanced Secure Erase ] implementations wipe all the memory blocks on SSD, on top of the data mapping table. But hardware manufacturers often do not disclose their specific implementations.

Security Freeze Lock

Further complicating the SSD wipe is [ Security Freeze Lock ] feature implemented in almost all the SSDs as a part of standard specs. Freeze locks were developed as a preemptive protection measure against malicious software attacks; A virus that triggers unsolicited erasure operations or locks the drive with a password unknown to the user, etc. While Freeze Lock is a useful protection measure, it becomes a major obstacle when one needs to wipe a SSD.

Removing [ Security Freeze Lock ] requires very complex procedures and right procedures widely vary depending on hardware implementations.

How DiskDeleter wipe SSD

To overcome these difficulties, DiskDeleter has implemented a method to treat a SSD as an external drive whereby Security Freeze  Locks are bypassed and secure erasure / enhanced secure erasure can be executed effectively.

DiskDeleter Kit includes a dedicated converter cable. By connecting this converter cable, internal SSD can be treated as an external drive and secure erase / enhanced secure erasure commands can be executed efficiently with ease.