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SSD Data Recovery Concepts and Methodologies

by Jeremy Brock President, A+ Perfect Computers - December 1, 2010
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SSD Data Recovery Concepts and Methodologies

W
e're often asked why data recovery of solid state drives is necessary. Many people have the perception that anything solid state from USB flash drives to SSDs are impervious to failure due to the lack of moving parts. While these drives are unlikely to fail from being dropped they have their own unique issues which impact their long term endurance such as wear damage, firmware bugs, or poor fault handling by the drives firmware.

A solid state drive's endurance is limited by thenumber of available spare blocks and the amount of error correcting code implemented to correct bit errors that develop from writing data over the lifetime of the drive. Solid state drives will transparently remap blocks of data to different locations so no one block is written to more frequently than another. The boom in solid state drive solutions has created a plethora of companies, controllers, and firmware versions with different implementations to address this problem. To successfully recover data from solid state drives requires an in-depth knowledge of how data is stored and addressed throughout NAND memory for that vendor's specific implementation.

At the core of a solid state drive is its remapping table, a data structure which translates LBA addresses to NAND block address allowing the controller to locate data. Most controllers tag each block of data with an address or store an array of addresses in a table somewhere in NAND. Addresses can be merged with status bits which obfuscate the actual address making locating these data structures difficult without knowing the encoding scheme beforehand.

In the last year a few companies have come out with canned / prepackaged data recovery solutions for recovering data from solid state drives. These solutions support a limited number of controllers, firmware and NAND memory configurations. To use these solutions data recovery shops remove the NAND memory chips, read their contents, then use a software application to process the NAND contents and generate a final image. Most controller/firmware/NAND combinations are only partially reverse engineered resulting in a poor or corrupt image. SSD bad block routines,damaged remapping tables and wear damage can also negatively affect the final image.

If the drive isn't supported by a 3rd party solution it's up to the data recovery shop to create their own solution. This typically involves locating file system data structures stored in predictable locations or purchasing an identical drive and writing test patterns to figure out how the controller is storing and addressing data. This process can take anywhere from a few weeks to a few months depending on the complexity of the drive.

In either case a full recovery can be complicated by the quality of data stored within the NAND memory chips and how gracefully the drive failed.Firmware bugs, sudden power loss, or the firmware's inability to handle a specific fault can leave the drives internal data structures or user data in an inconsistent state.Generally wear leveling algorithms effectively spread writes over the NAND media however in a few cases we've found one NAND chip has a statistically larger number of uncorrectable errors than its neighboring NAND chips. This can result in a poor final image as data is frequently interleaved between two or more NAND chips.
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Many new solid state drives are proactively using simple ciphers or military grade symmetric key encryption (eg: AES) which obfuscate the data stored in NAND memory. While simple cipher keys can be broken with frequency analysis, symmetric key encryption is nearly impossible to break without the manufacturer's help. Currently drives implementing symmetric key encryption algorithms are considered unrecoverable. In a climate of rush SSDs with buggy firmware this can be a dangerous combination ensuring the end users data is lost if the drive fails.

Data recovery of solid state drives is inherently complex. Due to advances in NAND storage concepts older drives (Pre 2009) tend to be more recoverable than newer (2010 and later) solid state drives. Over time and as the industry consolidates we may see an increase in the number of recoverable drives as more resources can be devoted to fewer drives. Locating a data recovery shop specializing in solid state drives can be tricky because few companies (small or large) have devoted any real time or money into independent research and development of solid state drives.

If you're in the unfortunate position that you need your data recovered from a solid state drive get a referral from the drives controller or SSD manufacture. Otherwise try searching for a data recovery shop that specializes in your specific drive or NAND data recovery as a whole. Avoid data recovery shops that specialize in EVERYTHING and be skeptical of shops that specialize primarily in hard drives as they likely won't have much experience in NAND or solid state drives.

Many data recovery shops won't tell you they don't know how to recover data from your drive so they might fabricate an excuse like the controller is bad, static electricity damaged the drive or the controller overwrote all your data. If a data recovery shop says your drive is unrecoverable try another company.

Most importantly BACKUP YOUR DATA!!!


Editor's footnotes and disclaimer

My editor's introduction had gotten so long and unwieldy - there was a distinct risk that readers wouldn't get to see any of the text by the author of the above article when they landed on this page. So I put it here at the end instead.

Data recovery for magnetic, optical and simple flash memory storage is a well established science and market that has received plenty of coverage here on StorageSearch.com since 1998. But what about SSDs? They're different. Some SSDs are more complicated internally than RAID systems. And there are many different ways of designing SSDs that even SSD architects disagree about.

I started talking to experts in traditional DR companies about the subject of SSD data recovery back in 2007. What I needed - I said - was someone who not only knew some of the theory - but also had enough experience of handling SSD recoveries to write a reliable introductory article on this topic for our readers.

Now when it comes to the subject of SSDs - I am a difficult editor to satisfy - because I've talked to more SSD companies (past, present and future) than anyone else on the planet. And the problem for SSD recovery companies is that because SSD recovery is still a small new market their expertise is limited to subset of what's actually out there - and consequently they may extrapolate a naiive view from the limited stuff they've seen. All that will change in the next few years. In the meantime - I needed an article now - while we're still at the start of the SSD market bubble. But who was going to write it?

And I had to make sure that I filtered out spammy companies - who just want your business - but don't know as much as they should. To be fair - nobody knows all the answers today.

A few months ago Jeremy Brock (the author of the article below) emailed me to say he disagreed with my suggestion that readers should filter out DR companies less than 5 years old who claimed they could do SSD recoveries. His company at the time was 3 years old - and specialized in flash storage.

Over a period of more than 30 very lengthy email exchanges (some of which were article length in themselves) I came around to the view that readers would definitely benefit from seeing an article written by the nearest thing that the market has today to an expert in comsumer SSD recoveries.

So that's how the article on this page was born.

I couldn't find a linkedin page or bio for Jeremy Brock - so I linked to some other articles he had previously written instead.

And now you can see why this couldn't go at the beginning. I'm just not very good at managing my own word counts in editorial.
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