RAID arrays are necessary to improve the reliability of data storage and increase the speed of working with disks by combining multiple disks into one large one. RAID arrays can be either hardware, firmware or software.
I will describe several types:
RAID 0 (stripe) – The mode is only for improving performance when reading/writing does not increase reliability. The user has access to the whole volume of disks, if one of the disks fails, the array is usually destroyed and data recovery is almost impossible.
RAID 1 (mirror) – On all disks the recording is performed synchronously, they completely duplicate each other. Half of the disk space is available to the user. Increases performance only when reading, but this is a very reliable way to protect information. The minimum number of disks is 2.
RAID 10 (RAID 1+0) – This is an array of RAID0 from RAID1 arrays. Fast as RAID0 and reliable as RAID1. The minimum number of disks is four and their number should be even. Half of the disk space is available to the user.
RAID 0 + 1 – RAID1 array from RAID0 arrays. Not popular, since the advantages are worse than RAID 10.
RAID 1E – Similar to RAID10 using an odd number of disks and a minimum of 3.
RAID 5 – User-accessible space is reduced by one disk, reliability is lower than RAID 1, performance is increased when reading and writing as in RAID 0. If one of the disks fails, the data can be restored. The minimum number of disks is 3.
RAID 6 – Similar to RAID 5, including speed, but a little more reliable. The space available to the user is reduced by two disks, the information is not lost when two disks fail. The minimum number of disks is 4.
I personally prefer to use RAID 1 and RAID 6.