SSD hard drives ... A blessing or a curse?
My personal idea: A curse!
Of course they are super fast. Anyone who has ever replaced a regular hard disk with an SSD is amazed at the speed.
At least, in the beginning.
When writing data to an SSD, memory must first be cleared before something new can be written. This is in contrast to a normal hard disk where you can immediately overwrite the old data.
That is why a new SSD is super fast. The memory is still completely empty and therefore does not need to be erased. However, once the disk has been in use for a while, new data can only be written if the old data is first erased. This wastes time.
That is why the TRIM command was introduced. This allows you to delete unused memory blocks when the hard disk has time to do so. This avoids having to first perform a delete operation when performing a new write operation.
However, the operating system must be equipped for this.
In the field of data recovery and forensic research, this is an nightmare, because the hard disk itself erases the unused data, without user intervention.
Suppose you accidentally delete a folder with photos, and only notice it a few days later.
On a regular hard disk there is there is still a good chance that we will recover most of it.
On an SSD hard disk with TRIM command it is very likely that we will not be able to retrieve anything anymore.
Why do I think SSDs are a curse?
As a Data Recovery professional, we are often confronted with SSDs that no longer work.
There are all kinds of reasons for this:
- A bug in the program that controls the SSD. These are teething problems that should normally go away after a while. Usually a firmware update is sufficient
- Poor quality of memory chips
- Electronic defect
For some years, when we had to replace memory chips read out to recover the data, we had a few bad sectors per chip.
If we do that with a modern chip, we sometimes find millions of bad sectors.
These 'bad sectors' are removed during the operation of the disc corrected by a so-called ECC code. This allows bit errors to be corrected.
When the quality of a memory chip deteriorates over time, the number of bit errors increases, to the point that the data can no longer be corrected. At best, you will have an unreadable sector, and at worst a defective SSD. Now certain manufacturers (such as Sandforce) think it is a good idea (to protect their algorithms from competitors). ) to encrypt the data on the memory chip.
This means that if the controller that controls the drive breaks down, no one can retrieve the data. The encryption key is baked into the controller.
Replacing the defective controller with a working one has no effect as the encryption key is different.
If the data is not encrypted, you will see we are confronted with a gigantic puzzle.
The data is not stored until one memory chip is full and then on to the next.
No, to limit the number of write operations per chip (a Nand chip can only perform a certain number of writes) the data is broken down, mixed with an XOR table and only then written to the different chips.
Each block of data that is written has its own address and ECC code.
At the Based on those addresses, the data must then be reassembled, the ECC correction applied, and then stored on another medium.
One can now of course think that this is not so difficult. It is sufficient to look up the addresses and put the blocks in the correct order, right?
Then one has not counted on the creativity of the designers.
Such an SSD is also full of so-called mixes (just like a USB stick and a flash card).
What is a mix? Well, to increase speed (and some other reasons) the data is split up and programmed into several chips at the same time.
A simple example: Suppose we have the following data (hexadecimal) 0A 12 45 BC and the SSD contains 4 memory chips.
Then it is not unusual to write 0A to the first chip, 12 to the second, 45 to the third and BC to the last.
Here I of course set it free simple, but there are very complicated mixes.
The advantage of this is that you can achieve a 4 times greater writing and reading speed.
The disadvantage is that the puzzle becomes much more complex, because this all needs to be sorted out.
There are still many factors involved, but that will be for a next article.
Which is a blessing for some (speed ) is a curse (recovery) for the other.