RAID1又称为Mirror或Mirroring，它的宗旨是最大限度的保证用户数据的可用性和可修复性。 RAID1的操作方式是把用户写入硬盘的数据百分之百地自动复制到另外一个硬盘上。由于对存储的数据进行百分之百的备份，在所有RAID级别中，RAID1提供最高的数据安全保障。同样，由于数据的百分之百备份，备份数据占了总存储空间的一半，因而，Mirror的磁盘空间利用率低，存储成本高。
Mirror虽不能提高存储性能，但由于其具有的高数据安全性，使其尤其适用于存放重要数据，如服务器和数据库存储等领域。
RAID1: Mirroring and Duplexing
Characteristics/Advantages
1. One Write or two Reads possible per mirrored pair
2. Twice the Read transaction rate of single disks, same Write transaction rate as single disks
3. 100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk
4. Transfer rate per block is equal to that of a single disk
5. Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures
6. Simplest RAID storage subsystem design
Disadvantages
1. Highest disk overhead of all RAID types (100%) - inefficient
2. Typically the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended
3. May not support hot swap of failed disk when implemented in “software”
Recommended Applications
1. Accounting
2. Payroll
3. Financial
4. Any application requiring very high availability
For Highest performance, the controller must be able to perform two concurrent separate Reads per mirrored pair or two duplicate Writes per mirrored pair.
RAID Level 1 requires a minimum of 2 drives to implement
