1 · Choose a RAID level
RAID 5 with an integrated hot spare (one drive of capacity reserved).
2 · Configure drives
3 · Drive class
3.5" nearline SAS/SATA capacity HDD — indicative figures.
Advanced — read/write mix, URE rate
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.
What RAID 5E is
RAID 5E is RAID 5 with a hot spare distributed into the array rather than sitting idle. Usable capacity is (n−2) × drive size — one drive for parity, one for the integrated spare — and it survives a single drive failure, after which the spare capacity absorbs the rebuild immediately.
Spreading the spare across all drives keeps every spindle working (slightly better performance than an idle dedicated spare) and starts the rebuild without waiting. The cost is a drive of usable capacity, the same ×4 write penalty as RAID 5, and the same single-parity rebuild exposure.
Six 8 TB drives in RAID 5E give 32 TB usable: four for data, one for parity, one for an integrated hot spare. A drive failure self-heals immediately into the spare capacity — at the cost of one usable drive versus plain RAID 5.
Advantages
- Integrated hot spare — immediate rebuild
- All spindles active (vs idle dedicated spare)
- Survives one failure then self-heals
- Familiar RAID 5 economics
Trade-offs
- (n−2) usable — a drive for parity + a drive for spare
- ×4 write penalty
- Single parity — rebuild has no safety net
- Less common than RAID 6 + global spare
Best for
- Arrays that want a built-in spare and fast failover
- Read-heavy workloads on modest drives
- Where idle dedicated spares are undesirable
Consider another level when
- Large drives (prefer RAID 6 for rebuild safety)
- Maximum usable capacity needs
- Write-heavy databases
RAID 5E — common questions
How is RAID 5E capacity calculated?
Usable capacity is (number of drives − 2) × drive size: one drive of distributed parity plus one drive of integrated hot-spare capacity. Six 8 TB drives give 32 TB usable.
RAID 5E vs RAID 5 with a hot spare?
Both reserve a drive of spare capacity. RAID 5E distributes the spare across all drives so every spindle works and the rebuild starts instantly; a separate hot spare sits idle until needed. Capacity is effectively the same.
Is RAID 5E safe on large drives?
It has the same single-parity rebuild exposure as RAID 5 — a URE during rebuild can cause data loss. On large nearline drives, RAID 6 (dual parity) plus a global spare is safer.