Hardware Raid Server Vs. Software Raid Server

Several hard drives can be grouped into arrays for speed or data safety.

RAID (Redundant Array of Inexpensive Disk) is a system that uses several hard drives to improve speed, data security or both. Two types of RAID system can be used. Software RAID uses the hard drives connected to the motherboard or add-on card and relies on software to manage the array. Hardware RAID uses a dedicated card with its own processor and RAM to do the same.

RAID Types

Software and hardware RAID both support the main RAID type 0, 1, 5, 10 and 50. RAID 0 or stripping is designed for speed, stripping the data between two of more drives, allowing the system to combine the bandwidth of both drives. If one drive fails, all the data is lost. RAID 1 uses two drives, one being maintained as a mirror to the other. If one drive fails, the data is still available on the other one. RAID 5 uses parity information. Parity is a set of data used to be able to rebuild data in case one drive fails. RAID 5 uses a minimum of three drives, but keeping the equivalent of one drive for parity information. If one drive fails the data can be rebuilt using that information. RAID 10 and 50 uses two RAID 1 or RAID 5 array in a RAID 0 configurations to add speed to data safety.

Read/Write Speed

The hardware RAID system will be faster than a software RAID system on average. How big that difference is will depend on what type of RAID is used and what operation is being performed. For reading data, the difference will be minimal. For writing data, the difference will be more important as the system needs to calculate parity information in RAID 5, divide the data between two discs in RAID 0 or write the same data on two discs in RAID 1. When rebuilding an array after a drive failure, the rebuilding speed of a hardware RAID system is significantly faster than a software RAID, as the RAID card has its own specialized processor that handles the rebuild instead of relying on the central processor.

Reliability

Data reliability when the system is working properly is equal between software and hardware RAID. However, in higher-end systems, hardware RAID can include a small battery that allows the data and the parity information to be written to the discs, even if the computer crashes. In software, the RAID function is not available and a crash can produce parity errors and possibly, loss of data.

Cost

Hardware RAID, depending on its level of sophistication cost between $250 and several thousand dollars. Software RAID is either included in the operating system (md under Linux for example) or with software provided with a low end SATA card costing $15 to $50 (prices as of 2010).

System Impact

The impact of a hardware RAID on the system is virtually null. The RAID card has its own processor and memory that manages the data sent by and to the operating system. Software RAID relies on the main processor and the software interface to manage the same functions. While the overhead of a software RAID system for a RAID 0 or 1 is low, the strain on the system will be non-negligible for a RAID 5 system, even if higher end computer with several processors will be less impacted than low end computers.

References

• University of Bridgeport: RAID