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Raid Options

If you wish, you may choose to have this Quiet PC set up with RAID.

What is RAID?

RAID (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, I/O (input/output) operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failures (MTBF), storing data redundantly also increases fault tolerance.

RAID 0 (Striping)

This technique has striping but no redundancy of data. It offers the best performance but no fault-tolerance.

RAID 1 (Mirroring)

This type is also known as disk mirroring and consists of at least two drives that duplicate the storage of data. There is no striping. Read performance is improved since either disk can be read at the same time. Write performance is the same as for single disk storage. RAID-1 provides the best performance and the best fault-tolerance in a multi-user system.

RAID 5

This type includes a rotating parity array, thus, all read and write operations can be overlapped. RAID-5 stores parity information but not redundant data (but parity information can be used to reconstruct data). RAID-5 requires at least three and usually five disks for the array. It's best for multi-user systems in which performance is not critical or which do few write operations

RAID 10

Combining RAID-0 and RAID-1 is often referred to as RAID-10, which offers higher performance than RAID-1 but at much higher cost. There are two subtypes: In RAID-0+1, data is organized as stripes across multiple disks, and then the striped disk sets are mirrored. In RAID-1+0, the data is mirrored and the mirrors are striped.

RAID Level 0 (Striping)

RAID Level 0 is the simplest RAID level, RAID 0 should really be called "AID", since it involves no redundancy. Files are broken into stripes of a size dictated by the user-defined stripe size of the array, and stripes are sent to each disk in the array. Giving up redundancy allows this RAID level the best overall performance characteristics of the single RAID levels, especially for its cost. For this reason, it is becoming increasingly popular by performance-seekers, especially in the lower end of the marketplace.

Hard Disk Requirements: Minimum of two hard disks (some may support one drive, the point of which escapes me); maximum set by controller. Any type may be used, but they should be of identical type and size for best performance and to eliminate "waste".
Array Capacity: (Size of Smallest Drive * Number of Drives).
Storage Efficiency: 100% if identical drives are used.
Fault Tolerance: None. Failure of any drive results in loss of all data, short of specialized data recovery.
Availability: Lowest of any RAID level. Lack of fault tolerance means no rapid recovery from failures. Failure of any drive results in array being lost and immediate downtime until array can be rebuilt and data restored from backup.
Degradation and Rebuilding: Not applicable.
Random Read Performance: Very good; better if using larger stripe sizes if the controller supports independent reads to different disks in the array.
Random Write Performance: Very good; again, best if using a larger stripe size and a controller supporting independent writes.
Sequential Read Performance: Very good to excellent.
Sequential Write Performance: Very good.
Cost: Lowest of all RAID levels.
Special Considerations: Using a RAID 0 array without backing up any changes made to its data at least daily is a loud statement that that data is not important to you.
Recommended Uses: Non-critical data (or data that changes infrequently and is backed up regularly) requiring high speed, particularly write speed, and low cost of implementation. Audio and video streaming and editing; web servers; graphic design; high-end gaming or hobbyist systems; temporary or "scratch" disks on larger machines.

RAID Level 1 (Mirroring)

RAID Level 1 is the pure implementation of data mirroring. In a nutshell RAID Level 1 gives you fault tolerance but it cuts your usable capacity in half and it offers excellent throughput and I/O performance. This RAID level is often used in servers for the system partition for enhanced reliability but PC enthusiasts can also get a nice performance boost from RAID Level 1. 50% of your purchased space will be used for duplication. Description: RAID 1 is usually implemented as mirroring; a drive has its data duplicated on two different drives using either a hardware RAID controller or software (generally via the operating system). If either drive fails, the other continues to function as a single drive until the failed drive is replaced. Conceptually simple, RAID 1 is popular for those who require fault tolerance and don't need top-notch read performance. A variant of RAID 1 is duplexing, which duplicates the controller card as well as the drive, providing tolerance against failures of either a drive or a controller. It is much less commonly seen than straight mirroring.

Hard Disk Requirements: Exactly two hard disks. Any type may be used but they should ideally be identical.
Array Capacity: Size of Smaller Drive.
Storage Efficiency: 50% if drives of the same size are used, otherwise (Size of Smaller Drive / (Size of Smaller Drive + Size of Larger Drive) )
Fault Tolerance: Very good; duplexing even better.
Availability: Very good. Most RAID controllers, even low-end ones, will support hot sparing and automatic rebuilding of RAID 1 arrays.
Degradation and Rebuilding: Slight degradation of read performance; write performance will actually improve. Rebuilding is relatively fast.
Random Read Performance: Good. Better than a single drive but worse than many other RAID levels.
Random Write Performance: Good. Worse than a single drive, but better than many other RAID levels.
Sequential Read Performance: Fair; about the same as a single drive.
Sequential Write Performance: Good; again, better than many other RAID levels.
Cost: Relatively high due to redundant drives; lowest storage efficiency of the single RAID levels. Duplexing is still more expensive due to redundant controllers. On the other hand, no expensive controller is required, and large consumer-grade drives are rather inexpensive these days, making RAID 1 a viable choice for an individual system.
Special Considerations: RAID 1 arrays are limited to the size of the drives used in the array. Multiple RAID 1 arrays can be set up if additional storage is required, but RAID 1+0 begins to look more attractive in that circumstance. Performance may be reduced if implemented using software instead of a hardware controller; duplexing may require software RAID and thus may show lower performance than mirroring.
Recommended Uses: Applications requiring high fault tolerance at a low cost, without heavy emphasis on large amounts of storage capacity or top performance. Especially useful in situations where the perception is that having a duplicated set of data is more secure than using parity. For this reason, RAID 1 is popular for accounting and other financial data. It is also commonly used for small database systems, enterprise servers, and for individual users requiring fault tolerance with a minimum of hassle and cost (since redundancy using parity generally requires more expensive hardware.)

RAID Level 5

RAID Level 5 is a cluster-level implementation of data striping with DISTRIBUTED parity for enhanced performance. Clusters can vary in size and are user-definable but they are typically blocks of 64 thousand bytes. The clusters and parity are evenly distributed across multiple hard drives and this provides better performance than using a single drive for parity. Out of an array with "N" number of drives, the total capacity is equal to the sum of "N-1? hard drives. For example, an array with 4 equal sized hard drives will have the combined capacity of 3 hard drives. This is the most common implementation of data striping with parity. In this example 25% of the storage purchased is used for duplication.

Hard Disk Requirements: Minimum of three standard hard disks; maximum set by controller. Should be of identical size and type.
Array Capacity: (Size of Smallest Drive) * (Number of Drives - 1).
Storage Efficiency: If all drives are the same size, ( (Number of Drives - 1) / Number of Drives).
Fault Tolerance: Good. Can tolerate loss of one drive.
Availability: Good to very good. Hot sparing and automatic rebuild are usually featured on hardware RAID controllers supporting RAID 5 (software RAID 5 will require down-time).
Degradation and Rebuilding: Due to distributed parity, degradation can be substantial after a failure and during rebuilding.
Random Read Performance: Very good to excellent; generally better for larger stripe sizes. Can be better than RAID 0 since the data is distributed over one additional drive, and the parity information is not required during normal reads.
Random Write Performance: Only fair, due to parity overhead; this is improved over RAID 3 and RAID 4 due to eliminating the dedicated parity drive, but the overhead is still substantial.
Sequential Read Performance: Good to very good; generally better for smaller stripe sizes.
Sequential Write Performance: Fair to good.
Cost: Moderate, but often less than that of RAID 3 or RAID 4 due to its greater popularity, and especially if software RAID is used.
Special Considerations: Due to the amount of parity calculating required, software RAID 5 can seriously slow down a system. Performance will depend to some extent upon the stripe size chosen.
Recommended Uses: RAID 5 is seen by many as the ideal combination of good performance, good fault tolerance and high capacity and storage efficiency. It is best suited for transaction processing and is often used for "general purpose" service, as well as for relational database applications, enterprise resource planning and other business systems. For write-intensive applications, RAID 1 or RAID 10 are probably better choices (albeit higher in terms of hardware cost), as the performance of RAID 5 will begin to substantially decrease in a write-heavy environment.

RAID Level 10 (Stripe of Mirrors)

RAID Level 10 uses mirroring and striping without parity. It is the most popular of the multiple RAID levels and combines the best features of striping and mirroring to yield large arrays with high performance in most uses and superior fault tolerance. RAID 10 is a stripe across a number of mirrored sets. RAID 10 has been increasing dramatically in popularity as hard disks become cheaper and the four drive minimum is legitimately seen as much less of an obstacle. RAID 10 provides better fault tolerance and rebuild performance than RAID 01. This array type provides very good to excellent overall performance by combining the speed of RAID 0 with the redundancy of RAID 1 without requiring parity calculations. RAID 10 provides better fault resilience and "rebuild" performance than RAID 01. Both array types provide very good to excellent overall performance by combining the speed of RAID 0 with the redundancy of RAID 1 without requiring parity calculations.

Minimum number of drives: 4
Strengths: Highest performance, highest data protection (can tolerate multiple drive failures).
Weaknesses: High redundancy cost overhead; Because all data is duplicated, twice the storage capacity is required; Requires minimum of four drives.
Hard Disk Requirements: An even number of hard disks with a minimum of four; maximum dependent on controller. All drives should be identical.
Array Capacity: (Size of Smallest Drive) * (Number of Drives ) / 2.
Storage Efficiency: If all drives are the same size, 50%.
Fault Tolerance: excellent
Availability: excellent
Degradation and Rebuilding: Relatively little
Random Read Performance: Very good to excellent.
Random Write Performance: Good to very good.
Sequential Read Performance: Very good to excellent.
Sequential Write Performance: Good to very good.
Cost: Relatively high due to large number of drives required and low storage efficiency (50%).
Special Considerations: Low storage efficiency limits potential array capacity.
Recommended Uses: Applications requiring both high performance and reliability and willing to sacrifice capacity to get them. This includes enterprise servers, moderate sized database systems and the like at the high end, but also individuals using larger IDE/ATA hard disks on the low end. Often used in place of RAID 1 or RAID 5 by those requiring higher performance; may be used instead of RAID 1 for applications requiring more capacity.

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