PowerEdge: Data Retention Occur with SSD or Nvme Drives Due to Prolonged Power off

Enterprise SSD and NVMe drives retain data within their NAND structure by using voltage levels which represent the stored data. This enables the drives to have many beneficial features such as high read and write speeds and low-latency. However, it also requires that these voltages are maintained for as long as the data is required to be stored. Drive firmware performs background tasks to maintain data consistency as part of its "data retention" feature-set.

SSD and NVMe devices which are powered-up carried out data retention tasks to refresh the static voltages within the NAND cells. Also, NAND wear-leveling is optimized and is performed whether the drives are idle or undergoing host I/O operations. 

In contrast, drives which are powered off for extended durations cannot carry out these data retention operations. Under certain circumstances, drives may be prone to reduced NAND cell voltages within the retained data which may lead to media or drive faults on resumption of operation.

The JEDEC SSD Standards JESD218 & JESD219 provide industry-wide requirements around data retention for SSD media. 

The standard requires SSD/NVMe drives to retain their data during a power-off period for a minimum duration of three months at the maximum level of rated endurance (that is in a fully consumed state in terms of write-endurance). 

It should be noted that data retention is negatively impacted by the following factors:

• The P/E cycles and TBW state (remaining endurance) of the drive
  • A drive which has had more P/E cycles or TBW have less retention capability than a new drive with few P/E cycles or TBW.
• Active temperature over the lifetime of the drive
  • The temperature of the NAND cells over the lifetime of the drive impacts the retention capability.
• Power-off temperature over the duration of the power-off event 
  • Drives which are in a powered-off state should be stored at an ambient temperature not exceeding 40 degrees C / 104 degrees F.

To prevent data retention concerns, Dell Technologies recommends that based on current technology, SSD/NVMe drives which contain user data are powered-up once every 2.5 months for a minimum duration of 3 weeks to allow background tasks to complete. As drive capacities increase, the duration they must be powered on is also extended. Alternatively a read operation on all used NAND cells triggers the data retention tasks and would be recommended on larger capacity drives. Servers that are powered off and in storage for longer than 3 months should be decommissioned and have data backed up until they can be returned to production use.

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