RAID 1 is written on the data disk (or set of data disks) as well as a mirror disk (or set of disks). During the 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. It is mandatory to have at least 2 disks for a RAID 1 array. Usually for bettering the performance, RAID 1 system is merged with RAID 0. At times it is referred to by their joint number i.e., a RAID 10 system.
Advantages
Provides excellent read speed with a write-speed most comparable with a single disk.
In case a disk fails, there is no necessity to re-build the data; it's enough if they are copied on to the replacement disk.
RAID 1 is a very straight forward technology.
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.
