RAID 0 (also known as Striping)
RAID 0 will use any number of disks and will merge them, creating one large logical volume. They are usually used to achieve high speeds. Such is possible because reading and writing happen from multiple disks at the same time.
However, this has a cost. RAID 0 does not offer redundancy at all. Loosing an individual hard drive will result in complete data loss.
To be honest, This RAID level is less reliable when compared on having a single hard drive, for example.
RAID 0 can be useful, for example for cache purposes, where speed is vital while losing data would not matter. In the short RAID 0 should only be used for SPEED scenarios.
RAID 1 ( Or mirroring)
In short, almost every use case of RAID 1 is where you have two identical hard drives, and they will have the data mirrored/copied.
The use of RAID 1 is mostly for redundancy. Imagine that you lose a hard drive. With RAID 1 you will remain with the system up, relying on the remaining hard drive.
The broken hard drive can be swapped most likely with no downtime (but exceptions may occur).
There is also some benefit on what matter increased read performance with this level of RAID; once data can actually be read off any of the existing hard drives in the array.
In parallel, there will be a slightly higher write latency due to the fact the data will be written to both hard drives.
RAID 5 and 6
RAID 5 requires at least 3 hard drives. RAID 6 requires at least 4.
RAID 5 and 6 use the concept of RAID 0 when it comes striping the data across multiple drives to increase performance. However, it introduces redundancy. For that, the parity of information is distributed across the hard drives.
I will not bore you with detailed technical aspects in this article. Instead, let’s focus on what you should know about RAID 5 and RAID 6 regarding losing hard drives.
With RAID 5 you can lose only one har drive. If you have more than one hard drive failing, your array is no longer healthy, and there is the loss of data.
RAID 6 allows you to have up to two failed hard drives before your array is compromised.
Both RAID 5 and RAID 6 will improve your read performance dramatically. Regarding writing to the hard drives, performance depends grandly on the RAID controller you chose for using and its computing capacities.
The fact that the RAID controller should be an independent component in your system is justified by the need to calculate the data parity and write it across all hard drives.
RAID 5 and RAID 6 are often good choices for file servers, standard web servers, archive solutions ( near and deep) and other systems where most of the I/O transactions are meant to be reading.
If you are planning to run heavy writing to the hard drive systems, these RAID levels of RAID are not the right choice. As an example, a database server would not perform well on a system with storage based on RAID 5 or 6
A Note on performance and hard drive loss and size of drives
A RAID 5 or 6 system is going to have a considerable impact in performance in the eventuality of losing a hard drive. The performance will have to be sacrificed to assure that the environment stays operational. When replacing the failed drive, the rebuilt process will have to start. Such a process will use a significant amount of the total performance of the array. The rebuild times are getting longer and longer, in line with the hard drives getting bigger and bigger.
RAID 10 can run with a minimum of 4 drives.
It combines RAID 1 and RAID 0. Usually, this is the type of RAID you would look for if you’re looking for speed and still having redundancy.
Let’s take the example of a four hard drives configuration. Two hard drives will be mirrored holding half of the striped data and on the other two, also mirrored, the other half of the data.
Practically such RAID level assures you that you can lose any single drive, and then perhaps a second drive, without losing data.
Bear in mind that like RAID 1, there will be only the capacity of half the drives, but read and write performance are improved.
Nested RAID levels
Also known as hybrid RAID. They combine two or more of the standard RAID levels. I promise I will write an article alone on these RAID Levels in the short future.