Effects of Temperature on SSD Endurance

Overview

Solid State Drive (SSD) endurance is defined as the amount of data that can be written to a flash-based drive before it becomes unreliable. The temperature the drive is stored at can have extreme effects on the reliability of the drive.

SSD Endurance and Temperature

SSD endurance is defined by the amount of data that can be written to a flash-based drive before it becomes unreliable, where reliability is dictated by being able to read data back from an unpowered drive after a set duration of unpowered storage.  For most drive endurance specifications reliability is defined as 12 months of storage at 40°C at the end of usable drive life.

The SSD endurance specification can change dramatically when used at extreme temperatures such as those commonly seen in industrial and embedded applications.  While operating temperature (particularly at cold temperatures) can have a negative impact on drive endurance, it is storage at hot temperatures that is the focus of this technical document.

Flash data retention is dependent on the ability to determine the level of charge stored in each flash cell.  Over time this charge deteriorates and must be refreshed else the data stored in the flash cell will be lost.  When the flash is powered, cells are periodically refreshed to “top off” and restore lost charge.  However when the flash is not powered (e.g. in storage) cells are not refreshed and charge degrades with time.  The rate of charge loss (detrapping) is related to the storage temperature, accelerated with higher temperatures, and slowing with lower.

The acceleration factor for storage at various temperatures can be calculated using the Arrhenius equation:

Where
Ea = Activation energy (1.1 eV for SSD flash)
k = Boltzmann’s constant (8.623 x 10-5 eV/°K)
T1 = Baseline temperature (°K), typically 313°K
T2 = Application storage temperature (°K)

Which gives us the following acceleration factors for various storage temperatures:

 Storage Temperature Acceleration Factor Max storage duration at end of drive life (°C) (°K) 85 358 168 2 days 80 353 101 4 days 75 348 60 6 days 70 343 35 10 days 65 338 20 18 days 60 333 11.5 32 days 55 328 6.5 56 days 50 323 3.5 104 days 45 318 1.9 192 days 40 313 1 365 days 35 308 0.52 1.9 years 30 303 0.26 3.8 years 25 298 0.13 7.8 years 20 293 0.062 16 years 15 288 0.029 34 years 10 293 0.013 75 years

One observation from this equation is that the rate of charge loss is greatly accelerated as storage temperatures go above 40°C.  For instance, at storage temperatures of 85°C the loss is 2 orders of magnitude faster than at 40°C.  This effectively shortens the storage duration from 1 year to 2 days at the end of drive life.

For more information on how to determine drive endurance and impact of storage temperature and duration to SSD life see Understanding SSD Life Expectancy