DWPD (Drive Writes Per Day) is a key SSD endurance metric that shows how many times the full capacity of an SSD can be written to per day over its warranty period without causing untimely failure. When a proposal specifies 3xDWPD, it requires SSDs that can be entirely overwritten three times each day throughout their warranted lifespan—this is considered a “mixed-use” endurance class for typical data center or high-write environments.
Understanding DWPD
DWPD measures how many full-capacity daily overwrites an SSD can handle, making it particularly relevant for intensive workloads like databases or transaction processing systems. For example, a 1TB SSD rated at 3 DWPD with a 5-year warranty can reliably be written with 3TB of data per day for five years without exceeding its endurance rating. This metric is especially useful for enterprise workloads and helps specify the right drive for expected write activity.
Relationship to TBW and Bathtub Curves
DWPD and TBW (Terabytes Written) are related measures of endurance. TBW provides the total write capacity over a drive’s life, while DWPD describes how this is spread per day across the warranty period. The calculation is
DWPD (Drive Writes Per Day) Calculation
Formula:
DWPD =
(TBW × 1000) ÷ (365 × Years of Warranty × Drive Capacity in GB)
Where:
- DWPD: Drive Writes Per Day
- TBW: Terabytes Written (the total amount of data the SSD can write in its lifetime)
- Years of Warranty: Number of years the SSD is covered under warranty
- Drive Capacity in GB: The total storage capacity of the SSD in gigabytes
Example: For a 1TB SSD (1000GB), 5-year warranty, 5500 TBW:
DWPD = (5500 × 1000) ÷ (365 × 5 × 1000)
DWPD = 5,500,000 ÷ 1,825,000 = 3.01
Choosing a drive with an adequate DWPD ensures that it remains in the flat “steady state” region of the bathtub curve, avoiding early wear-out and maintaining reliable performance through the usable lifecycle.
Endurance Tiers
- Write-intensive: ~10 DWPD (highest endurance, expensive)
- Mixed-use: ~3 DWPD (suitable for workloads with balanced reads/writes)
- Read-intensive: ~1 DWPD (lowest endurance, lower cost)
A requirement for 3xDWPD indicates a need for mixed-use SSDs, balancing cost and durability for medium to heavy write environments.
Practical Implications
Selecting SSDs by DWPD rather than just TBW provides a more granular way to evaluate real-world suitability, especially in mission-critical systems with predictable write patterns. Drives with a higher DWPD rating generally cost more but are essential where data integrity and consistent performance over time are critical.