RAID 1

RAID 1

RAID 1 (Redundant Array of Independent Disks, Level 1) is a storage configuration that provides data redundancy through disk mirroring. All data written to one disk is simultaneously written to another, creating an exact copy (or mirror) in real time.

It requires a minimum of two disks and can tolerate the failure of one (or more, depending on how many mirrors exist).

How It Works

In RAID 1, each disk in the array contains an identical copy of the data. If one disk fails, the system continues to operate using the remaining disk(s) without data loss or downtime.

Disk 1	Disk 2
Data A	Data A
Data B	Data B
Data C	Data C

This setup ensures data availability and integrity in the event of disk failure.

Advantages

• High fault tolerance — can survive disk failure
• Fast read speeds (can read from either disk)
• Simple implementation
• Ideal for critical data protection

Disadvantages

• Inefficient storage (usable space = 50%)
• No performance gain for write operations (writes go to all disks)
• Not suitable for high-capacity storage if disk count is limited

Common Use Cases

• Operating system drives in servers
• Workstations handling critical files
• Home and enterprise backup systems
• Systems where data integrity is prioritized over storage capacity

Example Setup

Using mdadm in Linux:

<syntaxhighlight lang="bash"> sudo mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc </syntaxhighlight>

Comparison with Other RAID Levels

Feature	RAID 1	RAID 0	RAID 5	RAID 6
Redundancy	Yes	No	Yes (1 disk)	Yes (2 disks)	Performance	Fast reads, normal writes	High	Balanced	Slower writes	Minimum disks	2	2	3	4	Storage efficiency	50%	100%	(N - 1)/N	(N - 2)/N	Fault tolerance	1 disk	None	1 disk	2 disks	Use case	Critical data, OS	Speed	Balanced	High fault tolerance

See Also

• RAID
• RAID 0
• RAID 5
• RAID 6
• Data redundancy
• mdadm