In addition to the standard RAID levels of 0-6, there are also nested or hybrid levels. Nested levels combine two or more standard RAIDs to improve performance or offer better protection against data loss. These levels are multiple arrays of a particular type that are grouped together in the form of a different type of array.
In this article, we'll take a look at some of the more common nested RAID levels and some of the features they offer.
RAID 0+1
RAID 0+1 is a combination of standard levels 0 and 1. This level requires a minimum of 3 drives with 4 drives being the most common setup. It allows you to create a mirror image of the data as with RAID 1 and share the data between drives as with RAID 0. The best way to describe it is as a combination of two separate 0 arrays that are combined together to form a level 1 array.
The 0+1 configuration is somewhat less fault tolerant than some other levels and two simultaneous disk failures would crash the system. For this reason, businesses and people with critical data tend to opt for different setups.
RAID 10
The configuration of a RAID 10 is the reverse of a RAID 0+1 in that it can be conceptualized as two separate level 1 arrays that are combined to form a single RAID 0 array. It requires a minimum of four hard drives to implement.
This type of configuration allows for very fast performance when reading data since it minimizes the amount of seeking required to locate any given data element. The downside is that if a failed drive in the array is not replaced, it can create a single point of failure which can crash the entire system. One way to get around this is to add a "hot spare" drive, that is, a hard disk drive that is not used in the array until one of the working drives crashes. When one drive fails, the hot spare drive automatically takes its place in the array.
RAID 30
RAID 30 is a combination of RAID 3 and RAID 0. It makes use of striping, which allocates separate data segments to different disks in the system, and a dedicated parity disk to store information that allows data to be reconstructed in the event of a drive failure.
RAID 50
RAID 50 arrays combine block level striping from RAID 0 and distributed parity from RAID 5. This requires at least 6 drives for implementation and is essentially 3 level 5 sets combined as a RAID 0 array. This type of array can tolerate a failure from any one of the drives in the level 5 arrays without losing any data. Once a drive has failed, though, it must be replaced as soon as possible as it creates a single failure point for the rest of the array.
RAID 51
RAID 51 consists of two RAID 5 arrays combined as a single RAID 1. This configuration has a high level of fault tolerance, all the disks in one of the level 5 arrays and one in the other can fail before there is any loss of data.
RAID 60
RAID 60 requires at least 8 hard drives and is essentially two separate RAID 6 arrays combined as a RAID 0. Up to two disks on each set could fail before you would lose any data. This setup increases both storage capacity and performance compared to a RAID 6 array. These arrays tend to be slightly slower than RAID 50 but they offer better data security.
RAID 100
This configuration is essentially two RAID 10s combined as a RAID 0 array. IN many cases the top level 0 array is implemented as a logical drive using software rather than a physical disk drive. This is usually the best choice for very large databases, giving you better read performance while lessening the load on individual controllers.
There are many other less common forms of nested RAID arrays, but these are the most usual setups. Each if these configurations comes with their own advantages and disadvantages. The RAID level that is best for you or your business depends on your own particular requirements. Some levels provide better protection against data loss, while others offer superior performance in either reading or writing data, or both. The decision comes down to how critical your data is for you or your business and whether performance or data security is the most important criteria for you.
In this article, we'll take a look at some of the more common nested RAID levels and some of the features they offer.
RAID 0+1
RAID 0+1 is a combination of standard levels 0 and 1. This level requires a minimum of 3 drives with 4 drives being the most common setup. It allows you to create a mirror image of the data as with RAID 1 and share the data between drives as with RAID 0. The best way to describe it is as a combination of two separate 0 arrays that are combined together to form a level 1 array.
The 0+1 configuration is somewhat less fault tolerant than some other levels and two simultaneous disk failures would crash the system. For this reason, businesses and people with critical data tend to opt for different setups.
RAID 10
The configuration of a RAID 10 is the reverse of a RAID 0+1 in that it can be conceptualized as two separate level 1 arrays that are combined to form a single RAID 0 array. It requires a minimum of four hard drives to implement.
This type of configuration allows for very fast performance when reading data since it minimizes the amount of seeking required to locate any given data element. The downside is that if a failed drive in the array is not replaced, it can create a single point of failure which can crash the entire system. One way to get around this is to add a "hot spare" drive, that is, a hard disk drive that is not used in the array until one of the working drives crashes. When one drive fails, the hot spare drive automatically takes its place in the array.
RAID 30
RAID 30 is a combination of RAID 3 and RAID 0. It makes use of striping, which allocates separate data segments to different disks in the system, and a dedicated parity disk to store information that allows data to be reconstructed in the event of a drive failure.
RAID 50
RAID 50 arrays combine block level striping from RAID 0 and distributed parity from RAID 5. This requires at least 6 drives for implementation and is essentially 3 level 5 sets combined as a RAID 0 array. This type of array can tolerate a failure from any one of the drives in the level 5 arrays without losing any data. Once a drive has failed, though, it must be replaced as soon as possible as it creates a single failure point for the rest of the array.
RAID 51
RAID 51 consists of two RAID 5 arrays combined as a single RAID 1. This configuration has a high level of fault tolerance, all the disks in one of the level 5 arrays and one in the other can fail before there is any loss of data.
RAID 60
RAID 60 requires at least 8 hard drives and is essentially two separate RAID 6 arrays combined as a RAID 0. Up to two disks on each set could fail before you would lose any data. This setup increases both storage capacity and performance compared to a RAID 6 array. These arrays tend to be slightly slower than RAID 50 but they offer better data security.
RAID 100
This configuration is essentially two RAID 10s combined as a RAID 0 array. IN many cases the top level 0 array is implemented as a logical drive using software rather than a physical disk drive. This is usually the best choice for very large databases, giving you better read performance while lessening the load on individual controllers.
There are many other less common forms of nested RAID arrays, but these are the most usual setups. Each if these configurations comes with their own advantages and disadvantages. The RAID level that is best for you or your business depends on your own particular requirements. Some levels provide better protection against data loss, while others offer superior performance in either reading or writing data, or both. The decision comes down to how critical your data is for you or your business and whether performance or data security is the most important criteria for you.