Nested RAID levels

[3] The usable capacity of a RAID 01 array is the same as in a RAID 1 array made of the same drives, in which one half of the drives is used to mirror the other half.

[4] At least four disks are required in a standard RAID 01 configuration, but larger arrays are also used.

Implementations supporting two disks such as Linux RAID 10 offer a choice of layouts.

[10] 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.

Because the reliability of the system depends on quick replacement of the bad drive so the array can rebuild, it is common to include hot spares that can immediately start rebuilding the array upon failure.

However, this does not address the issue that the array is put under maximum strain reading every bit to rebuild the array at the time when it is most vulnerable.

This level is recommended for applications that require high fault tolerance, capacity and random access performance.

[15] The following table provides an overview of some considerations for nested RAID levels.