• Nested RAID levels, also known as hybrid RAID, combine two or more of the standard RAID levelsto gain performance, additional redundancy or both, as a result of combining properties of different standard RAID layouts.

• Data centers require data redundancy and performance from their RAID arrays. RAID 0+1 and RAID 1+0 combine the performance benefits of RAID 0 with the redundancy benefits of RAID 1. They use striping and mirroring techniques and combine their benefits. These types of RAID require an even number of disks, the minimum being four. RAID 1+0 is also known as RAID 10 (Ten) or RAID 1/0. Similarly, RAID 0+1 is also known as RAID 01 or RAID 0/1. RAID 1+0 performs well for workloads that use small, random, write-intensive I/O.

• When nesting RAID levels, a RAID type that provides redundancy is typically combined with RAID 0 to boost performance. With these configurations it is preferable to have RAID 0 on top and the redundant array at the bottom, because fewer disks need to be regenerated if a disk fails. Thus, RAID 1+0 is preferable to RAID 0+1 but the administrative advantages of "splitting the mirror" of RAID 1 are lost. It should be noted, however, that the on-disk layout of blocks for RAID 1+0 and RAID 0+1 setups are identical so these limitations are purely in the software.

• RAID 0+1

  A RAID 0+1 (also called RAID 01), is a RAID level used for both replicating and sharing data among disks.The minimum number of disks required to implement this level of RAID is 3 but it is more common to use a minimum of 4 disks. The difference between RAID 0+1 and RAID 1+0 is the location of each RAID system — RAID 0+1 is a mirror of stripes although some manufacturers (e.g. Digital/Compaq/HP) use RAID 0+1 to describe striped mirrors, consequently this usage is now deprecated so that RAID 0+1 and RAID1+0 are replaced by RAID10 whose definition correctly describes the correct and safe layout ie striped mirrors. The usable capacity of a RAID 0+1 array is N/2.Smin, where N is the total number of drives (must be even) in the array and Smin is the capacity of the smallest drive in the array.

  

• RAID 1+0

  A RAID 1+0, sometimes called RAID 1&0 or RAID 10, is similar to a RAID 0+1 with exception that the RAID levels used are reversed RAID 10 is a stripe of mirrors. RAID 10, as recognized by the storage industry association and as generally implemented by RAID controllers, is a RAID 0 array of mirrors, which may be two-way or three way-mirrors, and requires a minimum of four drives. More than four disks are possible in RAID 10 and these larger arrays are common in professional applications.

  

Applications that benefit from RAID 1+0 include the following:

• High transaction rate Online Transaction Processing (OLTP)

• Large messaging installations

• Database applications that require high I/O rate, random access, and high availability

• In most cases RAID 1+0 provides better throughput and latency than all other RAID levels except RAID 0 which wins in throughput. Thus, it is the preferable RAID level for I/O-intensive applications such as database, email, and web servers, as well as for any other use requiring high disk performance.