What is RAID?
RAID commonly stands for Redundant Array of Inexpensive Disks. In a RAID two or more separate drives are put together to act like one. The benefits of this are to keep your data safe, to access your data faster, or some combination of the two. A RAID distributes data across volumes (or drives) in several different ways, depending on the level of RAID you choose.

SSDs are typically chosen in situations where speed and performance take a priority to cost considerations. As they have no moving parts, their ability to both write and read data on them is significantly faster than on a HDD (at least 8-10x faster.) And their failure rate is roughly .5% during each year of is operation, which significantly reduces the risk compared to a spinning HDD.

Because of the dramatic difference between the technologies of HDDs and SSDs, it’s important to state that some RAID implementations that are great for HDDs are not for SSDs, and vice versa.

Volume (logical) vs. Disk/Drive (physical)
When discussing data storage, it is important to understand the difference between logical and physical.
When someone says,
“I have a 160GB hard drive in my computer.” They are referring to the physical disk/drive.

When that same person says,
“There are two drives that show up on my computer.” They are referring to the logical disk/drive, which is referred to as a volume.

When a physical drive is split logically into different volumes, this is called partitioning.

When discussing RAID technology, it is important to be aware of the differences between the logical and physical storage references.

Firmware
Firmware is essentially a small piece of software that resides on a piece of hardware to provide core functionality to the device as well as interface it with software and other pieces of hardware.
Firmware provides a basic set of operating instructions for the hardware device such as a hard drive.

It helps to think of firmware as a very basic OS (operating system) for a specific piece of hardware.

For example, your digital camera may require special drivers to be installed on the OS in order for it to transfer photos.

It helps to think of firmware as a very basic OS (operating system) for a specific piece of hardware.

When Should I Use RAID?
RAID is extremely useful if uptime and availability are important to you or your business. Backups will help insure you from a catastrophic data loss. But, restoring large amounts of data, like when you experience a drive failure, can take many hours to perform. Those backups could be hours or days old, costing you all the data stored or changed since the last backup. RAID allows you to weather the failure of one or more drives without data loss and, in many cases, without any downtime.

RAID is also useful if you are having disk IO issues, where applications are waiting on the disk to perform tasks. Going with RAID will provide you additional throughput by allowing you to read and write data from multiple drives instead of a single drive. Additionally, if you go with hardware RAID, the hardware RAID card will include additional memory to be used as cache, reducing the strain put on the physical hardware and increase overall performance.

Note: We generally do not advise using a hardware RAID card for SSD volumes, as the additional cache isn’t necessary because of the speed of the SSDs themselves.

What Type of RAID Should I Use?
No RAID – Good if you are able to endure several hours of downtime and/or data loss due while you restore your site from backups.
RAID 0 – Good if data is unimportant and can be lost, but performance is critical (such as with cache).
RAID 1 – Good if you are looking to inexpensively gain additional data redundancy and/or read speeds. (This is a good base level for those looking to achieve high uptime and increase the performance of backups.)
RAID 5/6 – Good if you you have Web servers, high read environments, or extremely large storage arrays as a single object. This will perform worse than RAID 1 on writes. If your environment is write-heavy, or you don’t need more space than is allowed on a disk with RAID 1, RAID 1 is likely a more effective option.
RAID 10 – A good all-around solution that provides additional read and write speed as well as additional redundancy.

Software RAID vs Hardware RAID?

Software RAID
Software RAID is not always an included option in all of dedicated servers. This means there is NO cost for software RAID 1, and is highly recommended if you’re using local storage on a system. It is highly recommended that drives in a RAID array be of the same type and size.

Software-based RAID will leverage some of the system’s computing power to manage the RAID configuration. If you’re looking to maximize performance of a system, such with a RAID 5 or 6 configuration, it’s best to use a hardware-based RAID card when you’re using standard HDDs.

Hardware RAID
Hardware-based RAID requires a dedicated controller installed in the server. Steadfast engineers will be happy to provide you with recommendations regarding which hardware RAID care is best for you that is based on what RAID configuration you want to have. A hardware based RAID card does all the management of the RAID array(s), providing logical disks to the system with no overheard on the part of the system itself. Additionally, hardware RAID can provide many different types of RAID configurations simultaneously to the system. This includes providing a RAID 1 array for the boot and application drive and a RAID-5 array for the large storage array.

What Does RAID Not Do?

RAID does not equate to 100% uptime. Nothing can. RAID is another tool on in the toolbox meant to help minimize downtime and availability issues. There is still a risk of a RAID card failure, though that is significantly lower than a mechanical HDD drive failure.
RAID does not replace backups. Nothing can replace a well planned and frequently tested backup implementation!
RAID will not protect you against data corruption, human error, or security issues. While it can protect you against a drive failure, there are innumerable reasons for keeping backups. So do not take RAID as a replacement for backups. If you don’t have backups in place, you’re not ready to consider RAID as an option.
RAID does not necessarily allow you to dynamically increase the size of the array. If you need more disk space, you cannot simply add another drive to the array. You are likely going to have to start from scratch, rebuilding/reformatting the array. Luckily, Steadfast engineers are here to help you architect and execute whatever systems you need to keep your business running.
RAID isn’t always the best option for virtualization and high-availability failover. In those circumstances, you will want to look at SAN solutions, which Steadfast also provides.

Source: Steadfast , macsales , Wikipedia

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