RAID, Redundant Array of Independent Disks or Redundant Array of Inexpensive Disks, is a tool generally used to improve storage complicity, provide security and improve performance. Generally what happens is a disks are grouped together, mainly the same size disks, to increase storage capacity. Depending on the array type, you can gain a few advantages. A few of those advantages being protection against disk failures, downtime and data integrity.
Among the many arrays, there are a few that are commonly used for various reasons. Reasons being cost and integrity. RAID 0 for example, uses the capacity of two drives and combines them into single virtual drive. So, 2x 1TB drives will you have a 2TBs of space. The data is then striped across the two drives, meaning that half the data is stored on one drive and the other half is stored on another drive.
The idea behind this was to create an array that was only meant for performance, nothing else. Some companies will use this RAID type but not on critical servers. Since there is no fault tolerance.
RAID 1 on the other hand, is all about redundancy. Thus making sure your data is always copied and backed up on another drive. You see, Raid 1 employs a method called mirroring. Where one drive copies all the data from another. So, while you have two drives it appears as one. This is because one drive is active and one drive is passive. With this array, you receive fault tolerance and that’s where if one or two drives fail in an array ( depending on the array) it can continue working.
The two main drawbacks are performance and capacity. Performance is not the greatest because all that information that is being written to the primary drive also needs to be written to the passive drive. On top of the performance issue, there is capacity. Even though you have a total of 2TB (2x1TB = 2TB) only 1TB will be accessible because the other 1TB is passively being used to mirror the primary drive.
Working in a datacenter, I witnessed countless companies use RAID 1 for the main OS drives… while all of the other drives were in RAID5, 6, or 10. Again, we’ll get to those RAID types later on.