Linear Mode
Linear mode, also called append mode, writes data to a single array disk until it is full. Once the disk is full, data is written to the next disk in the array until all disks are full. This provides an easy way to use disks of different sizes in an array, so that no space is ever wasted. Like striping, linear mode is not technically a RAID, because no redundancy is provided. It was also not present in the original RAID specification. For clarity, I will use the term linear mode, rather than append mode, throughout the rest of the book.
Disk spanning
The term linear mode is unique to the Linux kernel’s implementation of RAID. Most hardware RAID vendors use the term disk spanning, or simply spanning, to refer to this type of end-to-end disk arrangement. The terms disk concatenation or concatenated disks are also used.
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