Drive writes per day (DWPD) is an endurance rating that manufacturers of NAND flash storage provide their customers. Unlike hard disk storage, solid state storage has a limited number of write/erase cycles before the oxide layer within the storage device's floating-gate transistors begins to break down, a process known as flash wear-out. The DWPD rating tells the customer how many times he can expect to overwrite the entire capacity of the solid state drive before it becomes unreliable.
DWPD will vary, depending upon whether the storage is intended for consumer or enterprise use. Consumer use solid state drives (SSDs) have a fixed endurance rating and capacity. Enterprise SSD manufacturers, on the other hand, may offer SSDs of varying endurance levels and capacities depending upon whether the workload will be read-intensive, write-intensive or mixed. For instance, a vendor might sell an enterprise SSD with a high-capacity option intended for read-intensive application workloads. Such a high-capacity enterprise SSD might offer an endurance of only one full DWPD, meaning the drive can write and rewrite data to full capacity once a day for the warrantied lifespan of the drive. Another enterprise SSD option from the same product family might support 25 DWPD at a lower capacity for use with write-intensive workloads.