Unfortunately, while the concept was technically correct, not everyone agreed that RAID was indeed inexpensive. Only recently, with the rapidly declining price of drives, and the advent of intuitive, cost-effective RAID hardware and software solutions like the ATA NitroCannon and RAID Toolbox respectively, has the market agreed that RAID truly can be inexpensive, yet provide users with the speed advantages talked about from the beginning.

RAID Benefits
The obvious initial benefit of RAID is speed, but, depending upon the level of RAID, there can also be a fault tolerance benefit. The Mean Time Between Failure (MTBF) of the array will be equal to the MTBF of an individual drive, divided by the number of drives in the array. Because of this, the MTBF of an array of drives would be too low for some application requirements. However, disk arrays can be made fault-tolerant by redundantly storing information in various ways.

Flavors of RAID
Five types of array architectures, RAID-1 through RAID-5, were defined by the Berkeley paper, each providing disk fault-tolerance and each offering different trade-offs in features and performance. In addition to these five redundant array architectures, it has become popular to refer to a non-redundant array of disk drives as a RAID-0 array. The benefit of RAID-0, aka "Striping" is pure speed. RAID Toolbox provides you with an easy-to-use interface for striping drives found in a JBOD (box, or enclosure full of drives, "Just a Bunch Of Drives") or striping drives through a RAID controller.

What is Striping?
Fundamental to RAID is "striping" (RAID level 0), a method of connecting multiple drives into one logical storage unit. Striping involves partitioning each drive's storage space into "stripes" or areas on the disk, which may be as small as one sector (512 bytes) or as large as multiple gigabytes. These stripes are then interleaved, so that the combined space is composed alternately of stripes from each drive. In effect, the storage space of the drives is shuffled like a deck of cards. The type of application environment, I/O or data intensive, determines whether large or small stripes should be used.

Most multi-user operating systems today, like NT and Unix, support overlapped disk I/O operations across multiple drives. However, in order to maximize throughput for the disk subsystem, the I/O load must be balanced across all the drives so that each drive can be kept busy as much as possible. In a multiple drive system without striping, the disk I/O load is never perfectly balanced. Some drives will contain data files that are frequently accessed – while other drives will only rarely be accessed. In I/O intensive environments, performance is optimized by striping the drives in the array with stripes large enough so that each record potentially falls entirely within one stripe. This ensures that the data and I/O will be evenly distributed across the array, allowing each drive to work on a different I/O operation, and thus maximize the number of simultaneous I/O operations that can be performed by the array.

In environments that are data intensive and single-user systems that access large records, small stripes can be used so that each record will span across all the drives in the array, each drive storing part of the data from the record. This speeds access of long record, since the data transfer occurs in parallel on multiple drives. Applications such as on demand video/audio, medical imaging and data acquisition, which utilize long record accesses, will achieve optimum performance with small stripe arrays.

Need for Speed?
Striped arrays deliver the best performance and data storage efficiency of any array type. The only draw back however is that striped, or RAID-0 does not provide redundancy, if one drive in the array crashes, the entire array crashes.

RAID Level -0 is typically defined as a non-redundant group of striped disk drives. RAID-0 arrays are usually configured with large stripes for I/O intensive applications, but may be sector-striped with synchronized spindle drives for single-user and data intensive environments that access long sequential records.

Mirror, Mirror
RAID-1 is better known as "disk mirroring". "Disk mirroring" is simply a pair of disk drives that store duplicate data, but appears to the computer as a single drive. Writes must go to both drives in a mirrored pair so that the information on the drives is kept identical. Each individual drive, however, can perform simultaneous read operations. Mirroring thus doubles the read performance of an individual drive and leaves the write performance unchanged. RAID-1 delivers the best performance of any redundant array, especially in multi-user environments.

What’s the difference between software and hardware RAID?
Software-based RAID is the most inexpensive way of entering the RAID market. RAID software simulates a dedicated RAID controller by running on top of the operating system and allowing RAID arrays to be created and assigned to the system without the requirement for any other hardware. For more information on CEI's software-based RAID solution, visit the RAID Toolbox datasheet.

Hardware RAID has all the benefits of software RAID with the exception that it has its own onboard processor to handle IO related tasks. For more information on CEI's hardware-based RAID solution, visit the ATA NitroCannon datasheet.

What Should I Use?
This depends on the type of application you are running and how sensitive your data is.

RAID 0 vs. RAID 1
RAID-0 (Striping) is the fastest and most efficient array type but offers no fault-tolerance. Striping is commonly used by people seeking top disk drive performance: Digital audio and video, large graphics and pre-press users and users looking to Stripe hardware RAID controllers together for even greater speed gains.

RAID-1 (Mirroring) is the array of choice for performance-critical, fault-tolerant environments. People who require fault tolerance commonly use mirroring. Banking and financial institutions, enterprise-level applications, medical imaging or basically anyone looking for a real-time backup of their data.

Hardware RAID vs. Software RAID:
Hardware RAID: CEI's hardware-based RAID solution, the ATA NitroCannon, is an internal PCI RAID card. The NitroCannon is installed inside of a PC and supports up to four internal IDE drives.

Software RAID: CEI's software-based RAID solution, RAID Toolbox, supports a large amount of disk drive interfaces, including: SCSI, IDE, Fibre Channel, USB and Firewire. These drives can be connected either internally or externally.

Summary
So whether you are looking for unparalleled speed gain (Striping) or fault tolerance (Mirroring) CEI’s ATA NitroCannon or RAID Toolbox offers you an affordable, easy-to-use package.