RAID 1 or Mirroring is an alternate RAID technique that provides protection against loss of data during disk failures. RAID 1 duplicates the stored data on multiple disks. At the time of disk failure, either the data drive or the mirror drive is put into use for recovering the data and thus the operation is not halted. The failed disk can be removed from the system and replaced with a new or good disk. Subsequently, the RAID microcode can be given instructions to copy the data from the old disk to the new one in order to restore the mirror protection. It is mandatory to have at least 2 disks for a RAID 1 array.
For better performance, RAID 1 system is merged with RAID 0, popularly known as RAID 10. It requires minimum of 4 drives to implement. RAID 10 provides advantages of both RAID 1 as well as RAID 0. However, this setup is very expensive to implement and causes more overhead.
Advantages
Provides excellent read speed with a write-speed most comparable with a single disk.
In case a disk fails, there is no need to rebuild the data; it's enough if they are copied on to the replacement disk.
Disadvantages
The effective or usable storage capacity is only half of the total disk capacity available. This is because all data gets written twice i.e. duplicated.
Hot swap of a failed disk is denied by Software RAID 1 solution. Hence replacement is not possible while the server is running. It is suggested that a hardware controller be used.
