Managing RAID on Linux

Name

Create and Build modes

Synopsis

mdadm --create mddevice [options] memberdevicesmdadm --build mddevice [options] memberdevices

The Create and Build modes are similar in that they are both used to create new arrays. However, Build mode is used only for backward compatibility, to create legacy arrays without a RAID superblock. Never use Build mode to create a new array.

Options

-C, --create

Creates a new array.

-B, --build

Creates an old-style array without a RAID superblock.

-c, --chunk=

Sets the array chunk-size in kilobytes. The chunk-size is a power of two between 4 and 4096. For example, -c128 or --chunk=128 sets a chunk-size of 128 KB. The default is 64 KB.

--rounding=

Sets the rounding factor, which linear mode uses to align I/O operations. The rounding factor is similar to chunk-size, with the exception that it does not distribute operations across multiple disks. The default value of 64 KB should be fine for most users. The same rules that apply to chunk-size apply to rounding (for example, --rounding=8 for 8 KB rounding).

-l, --level=

Specifies the RAID level: linear, RAID-0, RAID-1, RAID-4, or RAID-5. For Build mode, only linear and RAID-0 are supported. For example, type -l5 or --level=5 for RAID-5.

-p, --parity=, --layout=

Sets the parity algorithm for RAID-5. The parity algorithm options are left-asymmetric, right-asymmetric, left-symmetric, or right-symmetric. The best choice is left-symmetric (which is also the default). Choices may also be abbreviated as la, ra, ls, and rs. Examples ...