1 · Choose a RAID level
Mirror. An n-way mirror survives n−1 failures.
2 · Configure drives
3 · Drive class
12G SAS SSD — 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 1 is
RAID 1 writes an identical copy of your data to every drive in the mirror. A two-way mirror gives you one drive of usable capacity and survives a single failure; an n-way mirror survives n−1 failures at the cost of more drives.
Reads can be served from any copy, so read performance scales with the mirror width, while writes go to every member (write penalty ×2). RAID 1 is the standard for boot/OS drives and small, critical datasets where simplicity and fast rebuild matter more than capacity efficiency.
A two-way mirror of 8 TB SSDs gives 8 TB usable and keeps running if one drive dies — rebuild is a fast straight copy from the survivor. The trade-off is 50% efficiency: you bought 16 TB raw to use 8 TB.
Advantages
- Simple, fast rebuild — just copy from a surviving mirror
- Read performance scales with mirror width
- Low write penalty (×2)
- No parity-calculation overhead
Trade-offs
- Only 50% capacity efficiency (2-way)
- Capacity does not scale — adding drives adds copies, not space
- Write throughput limited to one drive
- Expensive per usable TB
Best for
- Boot / OS volumes
- Small business-critical datasets
- Two-drive NAS units
- Workloads needing predictable rebuilds
Consider another level when
- Large-capacity requirements
- Bulk file, backup or archive storage
- Where capacity efficiency is the priority
RAID 1 — common questions
How much usable space does RAID 1 give?
A two-way mirror gives you the capacity of one drive — two 8 TB drives give 8 TB usable (50% efficiency). Adding more drives to the mirror does not add space; it adds redundancy (an n-way mirror still gives one drive of capacity but survives n−1 failures).
Is RAID 1 faster than a single drive?
For reads, yes — requests can be balanced across copies. Writes are no faster (and slightly slower) because every copy must be written, giving a ×2 write penalty.
RAID 1 vs RAID 10 — what is the difference?
RAID 1 is a single mirror set. RAID 10 stripes across multiple mirror pairs, so it adds capacity and throughput while keeping mirror-style redundancy. Use RAID 1 for two drives; RAID 10 for four or more.