As part of my set of articles regarding RAID, today I will be writing about different types of controllers. If you remember in the first article I had touched on this subject a bit and now I will elaborate.
As mentioned previously, this technology is divided to several very popular and important RAID levels where each level is dedicated to providing different levels of fault tolerance and performance improvements. Keep in mind that the RAID level is not an indication of a better/worse RAID type (RAID 5 is no better than RAID 1), it is simply a label used to identify how the drives are combined. Each RAID type has its own strengths and weaknesses, the key to picking your RAID level is identifying what you want to achieve from your RAID.
The logical RAID is achieved by either a raid controller piece of hardware or software. Hardware RAID is a dedicated add-on card that’s usually added to the PCIe or PCI slots of the server and it manages the RAID array. It is designed to support different drive interfaces such as SCSI, SAS, SATA (which will be explained in a future nugget) and it’s the controller’s job to identify and work with those drives accordingly. Some controllers are capable of providing more types of RAID levels than the others, some have more cache (explained in a previous nugget) than the others and some have different function than the others. Once again, choosing the proper RAID controller is a dedicated task as well that needs to account for number of drives, total capacity after RAID, performance expectations, total cache and many more. Of course upgrades are always possible but a good practice would be to get it right on the first try.
The other type of RAID is a software RAID. This is a very limited and not usually the recommended option. The software RAID does not have a dedicated RAID controller and uses the resources of the host system. It comes integrated into the system motherboard which is why it must take resources from the host system. This RAID type can support SCSI, SAS and SATA but usually at a degraded level of performance. One of the biggest disadvantages of a software RAID is upon failure; rebuilding the RAID is done by the CPU which can overload the system and completely disable all other activity until the task is complete. Software RAID is usually the chosen option when RAID performance isn’t a primary concern or if the budget constraints are extra strict.