RAID-DP calculator

NetApp double parity on WAFL — RAID 6 resilience without the ×6 write penalty. Set your drives below for live usable capacity, fault tolerance, IOPS, rebuild time and URE risk.

1 · Choose a RAID level

Stripe & mirror

Single parity

Dual / triple parity

Nested

ZFS RAID-Z

NetApp double parity on WAFL. Capacity & fault tolerance as RAID 6.

2 · Configure drives

Number of drives (min 4)

Capacity per drive (TB)

3 · Drive class

12G SAS SSD — indicative figures.

Advanced — read/write mix, URE rate

Workload mix: 70% read / 30% writeDrive URE rate

RAID-DP · 14 × 8 TB

96 TB usable

of 112 TB raw · 85.71% efficiency

Fault tolerance2 drives

Write penalty×2

IOPS estR ≈1.1M · W ≈525K · mix ≈808K

Throughput estR ≈12K · W ≈12K MB/s

Rebuild / drive est≈ 4.4 h

URE on rebuild risk8.8%

With redundancy still remaining during a single-drive rebuild, a URE here is reconstructed (recoverable) — not data loss. Data loss requires a concurrent second failure. Figure shown is the chance of encountering a URE.

Calculated for planning. We don't publish prices — a 24-year UK reseller, Servnet confirms the exact drives, array and pricing on quote. IOPS, throughput & rebuild are indicative estimates.

Overview

What RAID-DP is

RAID-DP is NetApp’s double-parity scheme: usable capacity is (n−2) × drive size and it survives any two drive failures — the same capacity and resilience as RAID 6. It is the default protection in NetApp ONTAP systems.

The difference is performance. Because RAID-DP runs on WAFL, which writes data to free space in full stripes rather than overwriting in place, it avoids the read-modify-write cost that gives classic RAID 6 a ×6 write penalty. So RAID-DP delivers dual-parity protection without the usual write tax — a vendor-specific behaviour we model rather than applying a misleading ×6.

At a glance

Usable capacity(n − 2) × drive size

Minimum drives4

Fault tolerance2 drives

Write penaltyWAFL full-stripe (≈ not ×6)

Worked example

14 × 8 TB SAS SSD → 96 TB usable, survives 2

Fourteen 8 TB drives in RAID-DP give 96 TB usable and tolerate any two failures — RAID 6-class protection, but WAFL full-stripe writes mean it sidesteps the ×6 write penalty that classic RAID 6 carries.

Advantages

Survives any two drive failures
WAFL full-stripe writes avoid the RAID-6 ×6 penalty
Default, mature protection in NetApp ONTAP
URE during single-drive rebuild is recoverable

Trade-offs

Two drives of capacity to parity
Vendor-specific (NetApp WAFL)
Performance is system-/workload-dependent
Not a generic controller option

Best for

NetApp ONTAP (AFF / FAS / ASA) systems
Mixed enterprise workloads needing dual parity
Where RAID 6 resilience is wanted without its write tax

Consider another level when

Non-NetApp arrays (use RAID 6)
Where a simple vendor-neutral level is required

Compare other levels

RAID 6 →RAID-TEC →RAIDZ2 →All levels →

RAID-DP — common questions

How is RAID-DP usable capacity calculated?

Usable capacity is (number of drives − 2) × drive size — the same as RAID 6 — because two drives hold dual parity. Fourteen 8 TB drives give 96 TB usable.

Does RAID-DP have the RAID 6 write penalty?

No, not the classic ×6. RAID-DP runs on NetApp WAFL, which coalesces writes and commits full stripes (including parity) to free space, avoiding the read-modify-write cycle. Effective write performance is far better than a naïve ×6 model suggests — it is workload- and system-specific.

RAID-DP vs RAID 6?

Same usable capacity and two-drive fault tolerance. RAID-DP is NetApp-specific and avoids the RAID-6 write penalty via WAFL; RAID 6 is the generic, vendor-neutral equivalent on standard controllers.