Earlier this year, there was some controversy
about heat and SSD data life when left unpowered. We don't think this is a major problem for most users, as a SSD will be powered for essentially its entire operational life -- but it may be an issue going forward, as users collect older technologies for re-use, given the generally long life of Apple hardware. So, in conjunction with our SSD Trim testing, we've started real-life testing of unpowered, depleted SSDs, exposed to high temperatures for extended periods of time to check on both data retention, as well as drive survivability.
We've been given access to a temperature- and humidity-controlled chamber. The temperature has been set to 160F, and 50 percent humidity for the duration of the test. We've been given seven 250GB Samsung 840 EVO SSDs that have all seen 600TB or more of data copies, and been taken off service. Eight others of the same make and model are factory fresh.
We've formatted all the drives, and are using a 200GB subset of the data we've been using for the Trim testing. Six of the depleted drives, and six of the factory-fresh drives, are already headed to the test chamber later today. One pair of depleted and fresh drives are sitting in a cabinet near our home server, and will remain untouched for the full year as a control.
As an additional control, we've taken one of the new drives with the same data, and installed it into a USB 3.0 external forensics case with ventilation, preventing writes by the OS or accidental erasure, and connected it to our home server where it will remain powered but unaltered for the duration of the test. We also have two other copies of the data on archival media in the case of an accident or failure of the SSD.
This is a long-term test. Every two months, we'll pull out one factory-fresh drive, and one older drive. We'll then install them both in forensics drive cases, preventing writing to the drive by the OS, and compare checksums to our control data on archival media as well as the powered SSD.
We'll repeat this process every two months for a year. Additionally, we'll put the drives we pulled out of climate control for testing and comparison back in and pull them all out in two years, for a second year of data -- the first drive we test will have been in the 160F environment for 22 months at that point after reinsertion.
The test won't be completely conclusive. The effect of cosmic rays is somewhat lessened in the climate chamber. Radiation levels inside the test chamber is 7.1 µrem per hour (0.071 µSv), and inside the case connected to the home server is 8.2 µrem per hour. Both of these numbers are slightly less than the background radiation of 10.4 µrem per hour in the location of the test chamber, and 9.8 µrem per hour at the home server's location (variances due to building materials, in all likelihood). We're working with our test partners on drive radiation exposure testing, but we're not ready to start that yet.
Furthermore, the testing is being performed on Samsung's TLC SSD media -- not universal to all manufacturers. However, other manufacturers now have similar processes, and we expect that it will be more widely adopted going forward.
So, come back every few months. We'll see where this takes us.