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What is RAID?
RAID is an acronym for "Redundant Array of Inexpensive Disks". The RAID standards define a variety of ways to merge multiple (usually inexpensive) drives into a single virtual drive (an array).
What are the different RAID levels?
RAID 0: Striping. RAID 0 increases the chance of data loss but provides the full space of all drives. It also potentially increases performance. At least 2 drives are needed.
RAID 1: Mirroring: RAID 1 substantially decreases the chance of data los but only provides 1/2 the space of all drives. It also potentially increases performance, though less than RAID 0. At least 2 drives are needed.
RAID 0+1: RAID 0+1 substantially decresases the chance of data loss. It only provides 1/2 the space of all drives, like RAID 1. It also provides some of the performance benefits of RAID 0. At least 4 drives are needed.
RAID 5: RAID 5 substantially decreases the chance of data loss. It only provides 2/3 the space of all drives, more than RAID 1 but less than RAID 0. It also provides some of the performance benefits of RAID 0. At least 3 drives are needed.
Why was RAID created?
It used to be that there were two types of hard drives: inexpensive ones that broke frequently, and expensive ones that were more reliable. RAID was created to make use of multiple inexpensive drives (still a cheaper option then a reliable drive at the time) to create a single, reliable drive.
This is the redundancy in RAID. All RAID levels (except for RAID 0) allow for the loss of at least one drive without the loss of any data. If a drive in an (non RAID-0) array fails, it can be replaced without the need to restore a backup and without any data loss.
RAID turns many unreliable drives into a single reliable drive.
But what about RAID 0?
RAID 0 is not truly RAID. The MTBF two-drive RAID 0 array is the square of the MTBF of a single drive. For example, if a single drive fails every ten years on average, the RAID array will fail, on average, every 3.2 years.
Doesn't RAID 0 give performance benefits?
Yes, it does. But you probably won't notice them. Although a two-drive RAID 0 array theoretically delivers twice the read and write performance of a single drive, it does not offer a significant real-world advantage in most applications.
There are two criteria that determine disk performance: latency and transfer. Latency (seek time) is the amount of time that it takes to actually access a piece of information on the disk. A faster spinning drive (such as the WD Raptor) decreases the part of seek time spent waiting for the platter to get to the right position. A faster moving actuator decreases the other part of seek time. Fast drives like the WD Raptor have both a low rotational latency (because of their fast spinning platter) and a low head latency (becuase of a fast moving actuator). The WD Raptor is a drive that minimizes seek times.
The other part of drive performance is transfer rate. This is how much data the drive can read per second once the head is already positioned. This is determined by two factors: how fast the platters are moving (rotational speed - RPM) and how many bits are packed in each inch (platter density). A fast moving drive like the WD Raptor has a high transfer rate because it spins quickly. Similarly, drives like the Maxtor DiamondMax 10 have a high transfer rate because they pack a lot of bits in a small area on the drive.
RAID uses two drives to increase transfer rate. It does not, however, improve seek times. Most applications (and games) read a lot of files in a somewhat random order. The drive spends all of its time doing seeks and does not actually achieve its transfer rate. Thus, a RAID 0 array does not improve performance significantly.
A drive like the WD Raptor, however, is an ideal choice for gaming as it decreases seek times and does significantly lower loading times.
What if I work with large files? Will RAID 0 help me?
Perhaps. RAID 0 can be effective with large sequential reads or writes. Yet, this is rarely the case. If you are dealing with massive quantities of data (e.g. uncompressed HD video), RAID can be a real asset. Most people, however, would be better served with a single faster drive.
What is the downside of RAID 0?
Reliabilty. A RAID 0 system is far more likely to lose data than a single drive.
What about RAID 1? Why would I want that?
RAID 1 is a good solution if you have important data. Although you do not get additional performance when writing, read performance is improved. RAID 1 trades data space for read performance and reliability. A RAID 1 array allows you to continue working even if one of your drives dies. If you use your computer for business (e.g. bookkeeping, customer info, writing, artwork, programming, etc.), RAID can be an important part of an overall disaster recovery strategy. Keep in mind, however, that RAID 1 only gives you the space of one drive in a two-drive array.
What about RAID 0+1?
RAID 0+1 combines RAID 0 and RAID 1 to create an array that is both reliable and fast. RAID1 has the reliability benefits of RAID 1 and the performance benefits of RAID 0. It requires at least 4 drives, however, and it wastes 50% of the total drive space. For these reasons, RAID 5 is a better option if your system supports it.
RAID is an acronym for "Redundant Array of Inexpensive Disks". The RAID standards define a variety of ways to merge multiple (usually inexpensive) drives into a single virtual drive (an array).
What are the different RAID levels?
RAID 0: Striping. RAID 0 increases the chance of data loss but provides the full space of all drives. It also potentially increases performance. At least 2 drives are needed.
RAID 1: Mirroring: RAID 1 substantially decreases the chance of data los but only provides 1/2 the space of all drives. It also potentially increases performance, though less than RAID 0. At least 2 drives are needed.
RAID 0+1: RAID 0+1 substantially decresases the chance of data loss. It only provides 1/2 the space of all drives, like RAID 1. It also provides some of the performance benefits of RAID 0. At least 4 drives are needed.
RAID 5: RAID 5 substantially decreases the chance of data loss. It only provides 2/3 the space of all drives, more than RAID 1 but less than RAID 0. It also provides some of the performance benefits of RAID 0. At least 3 drives are needed.
Why was RAID created?
It used to be that there were two types of hard drives: inexpensive ones that broke frequently, and expensive ones that were more reliable. RAID was created to make use of multiple inexpensive drives (still a cheaper option then a reliable drive at the time) to create a single, reliable drive.
This is the redundancy in RAID. All RAID levels (except for RAID 0) allow for the loss of at least one drive without the loss of any data. If a drive in an (non RAID-0) array fails, it can be replaced without the need to restore a backup and without any data loss.
RAID turns many unreliable drives into a single reliable drive.
But what about RAID 0?
RAID 0 is not truly RAID. The MTBF two-drive RAID 0 array is the square of the MTBF of a single drive. For example, if a single drive fails every ten years on average, the RAID array will fail, on average, every 3.2 years.
Doesn't RAID 0 give performance benefits?
Yes, it does. But you probably won't notice them. Although a two-drive RAID 0 array theoretically delivers twice the read and write performance of a single drive, it does not offer a significant real-world advantage in most applications.
There are two criteria that determine disk performance: latency and transfer. Latency (seek time) is the amount of time that it takes to actually access a piece of information on the disk. A faster spinning drive (such as the WD Raptor) decreases the part of seek time spent waiting for the platter to get to the right position. A faster moving actuator decreases the other part of seek time. Fast drives like the WD Raptor have both a low rotational latency (because of their fast spinning platter) and a low head latency (becuase of a fast moving actuator). The WD Raptor is a drive that minimizes seek times.
The other part of drive performance is transfer rate. This is how much data the drive can read per second once the head is already positioned. This is determined by two factors: how fast the platters are moving (rotational speed - RPM) and how many bits are packed in each inch (platter density). A fast moving drive like the WD Raptor has a high transfer rate because it spins quickly. Similarly, drives like the Maxtor DiamondMax 10 have a high transfer rate because they pack a lot of bits in a small area on the drive.
RAID uses two drives to increase transfer rate. It does not, however, improve seek times. Most applications (and games) read a lot of files in a somewhat random order. The drive spends all of its time doing seeks and does not actually achieve its transfer rate. Thus, a RAID 0 array does not improve performance significantly.
A drive like the WD Raptor, however, is an ideal choice for gaming as it decreases seek times and does significantly lower loading times.
What if I work with large files? Will RAID 0 help me?
Perhaps. RAID 0 can be effective with large sequential reads or writes. Yet, this is rarely the case. If you are dealing with massive quantities of data (e.g. uncompressed HD video), RAID can be a real asset. Most people, however, would be better served with a single faster drive.
What is the downside of RAID 0?
Reliabilty. A RAID 0 system is far more likely to lose data than a single drive.
What about RAID 1? Why would I want that?
RAID 1 is a good solution if you have important data. Although you do not get additional performance when writing, read performance is improved. RAID 1 trades data space for read performance and reliability. A RAID 1 array allows you to continue working even if one of your drives dies. If you use your computer for business (e.g. bookkeeping, customer info, writing, artwork, programming, etc.), RAID can be an important part of an overall disaster recovery strategy. Keep in mind, however, that RAID 1 only gives you the space of one drive in a two-drive array.
What about RAID 0+1?
RAID 0+1 combines RAID 0 and RAID 1 to create an array that is both reliable and fast. RAID1 has the reliability benefits of RAID 1 and the performance benefits of RAID 0. It requires at least 4 drives, however, and it wastes 50% of the total drive space. For these reasons, RAID 5 is a better option if your system supports it.
