Digital evidence storage for legal matters is a common practice. As the use of Solid State Drives (SSD) in consumer and enterprise computers has increased, so too has the number of SSDs in storage increased. When most, if not all, of the drives in storage were mechanical, there was little chance of silent data corruption as long as the environment in the storage enclosure maintained reasonable thresholds. The same is not true for SSDs.
A stored SSD, without power, can start to lose data in as little as a single week on the shelf.
SSDs have a shelf life. They need consistent access to a power source in order for them to not lose data over time. There are a number of factors that influence the non-powered retention period that an SSD has before potential data loss. These factors include amount of use the drive has already experienced, the temperature of the storage environment, and the materials that comprise the memory chips in the drive.
The Joint Electron Device Engineering Council (JEDEC) defines standards for the microelectronics industry, including standards for SSDs. One of those standards is an endurance rating. One of the factors for this rating is that an SSD retains data with power off for the required time for its application class.
For client application SSDs, the powered-off retention period standard is one year while enterprise application SSDs have a powered-off retention period of three months. These retention periods can vary greatly depending on the temperature of the storage area that houses SSDs.
In a presentation by Alvin Cox on JEDEC's website titled "JEDEC SSD Specifications Explained" [PDF warning], graphs on slide 27 show that for every 5 degrees C (9 degrees F) rise in temperature where the SSD is stored, the retention period is approximately halved. For example, if a client application SSD is stored at 25 degrees C (77 degrees F) it should last about 2 years on the shelf under optimal conditions. If that temperature goes up 5 degrees C, the storage standard drops to 1 year.
The standards change dramatically when you consider JEDEC's standards for enterprise class drives. The storage standard for this class of drive at the same operating temperature as the consumer class drive drops from 2 years under optimal conditions to 20 weeks. Five degrees of temperature rise in the storage environment drops the data retention period to 10 weeks. Overall, JEDEC lists a 3-month period of data retention as the standard for enterprise class drives.
A check of various drive manufacturers, in this case Samsung, Intel, and Seagate, shows that their ratings for data retention of their consumer class drives are what would be expected for JEDEC's enterprise class drive standards. All three quote a nominal 3-month retention time period. Most likely, the manufacturers are being conservative; however, it demonstrates the potential variability the manufacturers associate with data retention on any SSD in storage.
When you receive a computer system for storage in legal hold, drive operating and ambient storage temperature are probably not the first things on tap to consider. You cannot control the materials that comprise the drive and the prior use of the drive. You can control the ambient temperature of the storage which will potentially aid in data retention. You can also ensure that power is supplied to the drives while in storage. More importantly, you can control how the actual data is retained.
The easiest way to manage the problem is to image the drive in a timely manner. If long term storage is required, image the SSD onto a mechanical drive and place that drive in storage as well as the SSD. If you maintain an online legal hold storage capability, image the SSD to that storage. Either way, you essentially eliminate potential data retention problems. The worst-case scenario is explaining to the court why your data cannot be accessed because the hard drive you placed into storage is throwing out errors.
What started this look into SSDs? An imaging job of a laptop SSD left in storage for well over the 3-month minimum retention period quoted by the manufacturer of the drive before it was turned over to us. This drive had a large number of bad sectors identified during the imaging period. Not knowing the history, I did not consider the possibility of data loss due to the drive being in storage. Later, I learned that the drive was functioning well when it had been placed into storage. When returned to its owner a couple of months after the imaging, the system would not even recognize the drive as a valid boot device. Fortunately, the user data and files were preserved in the drive image that had been taken, thus there was no net loss.
Now imagine a situation in which an SSD was stored in legal hold where the data was no longer available for imaging, much less use in court. Ignorance of the technology is no excuse, and I am sure the opposing counsel would enjoy the opportunity to let the court know of the "negligent" evidence handling in the matter.
Bottom line - image it now … and use a mechanical disk.
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