RAID 1E calculator

Striped mirroring — RAID 10-style protection across an odd drive count. 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

Striped mirroring across an odd disk count. Survives ≥1; more if losses are not adjacent.

2 · Configure drives

Number of drives (min 3)

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 1E · 5 × 4 TB

8 TB usable

of 20 TB raw · 40% efficiency

Fault tolerance1 guaranteed (more if failures are not adjacent)

Write penalty×2

IOPS estR ≈375K · W ≈188K · mix ≈288K

Throughput estR ≈5K · W ≈2K MB/s

Rebuild / drive est≈ 2.2 h

URE on rebuild risk0.35%

During a single-drive rebuild there is no remaining redundancy — a URE on a surviving drive means data loss for the affected stripe. Real controllers mitigate via patrol reads/scrubs, so field results are often better.

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 1E is

RAID 1E (striped mirroring) spreads mirrored copies across all drives, so it works with an odd number of drives where RAID 10 needs an even count. Usable capacity is about half the raw (⌊n/2⌋ × drive size), and it guarantees surviving one drive failure.

Like RAID 10 it has a light ×2 write penalty and rebuilds from a surviving copy. It can survive more than one failure if the lost drives do not hold copies of the same data, but the guaranteed figure is one — which is what the calculator reports.

At a glance

Usable capacity⌊n/2⌋ × drive size (~50%)

Minimum drives3

Fault tolerance1 guaranteed

Write penalty×2

Worked example

5 × 4 TB SAS SSD → 8 TB usable, survives 1

Five 4 TB drives in RAID 1E give 8 TB usable with mirror-style protection on an odd drive count — handy when a five-bay server wants RAID 10-like resilience without leaving a bay empty.

Advantages

Works with odd drive counts (3, 5, 7…)
Low ×2 write penalty
Fast mirror-style rebuilds
Good random read performance

Trade-offs

~50% capacity efficiency
Only one failure guaranteed
Less common — controller support varies
Not as widely understood as RAID 10

Best for

Three- or five-drive servers needing mirror-style protection
Read-heavy workloads on odd drive counts
Where RAID 10 is wanted but the bay count is odd

Consider another level when

Even drive counts (use RAID 10)
Capacity-led bulk storage
Maximum resilience needs (use dual parity)

Compare other levels

RAID 10 →RAID 1 →RAID 5 →All levels →

RAID 1E — common questions

How is RAID 1E capacity calculated?

Usable capacity is the number of drives divided by two, rounded down, times the drive size — about 50% efficiency. Five 4 TB drives give ⌊5/2⌋ × 4 = 8 TB usable.

RAID 1E vs RAID 10?

Both give ~50% efficiency, a ×2 write penalty and mirror-style rebuilds. RAID 10 needs an even number of drives (mirror pairs); RAID 1E spreads copies across any count, including odd numbers, which is its main reason to exist.

How many drives can RAID 1E lose?

One is guaranteed. It may survive more if the failed drives do not both hold copies of the same stripe, but you should plan around the guaranteed figure of one.