dmraid - device-mapper RAID tool

Device-mapper, the new Linux 2.6 kernel generic device-mapping facility, is capable of mapping block devices in various ways (e.g. linear, striped, mirrored). The mappings are implemented in runtime loadable plugins called mapping targets.

These mappings can be used to support arbitrary software RAID solutions on Linux 2.6, such as ATARAID, without the need to have a special low-level driver as it used to be with Linux 2.4. This avoids code-redundancy and reduces error rates.

Device-mapper runtime mappings (e.g. map sector N of a mapped device onto sector M of another device) are defined in mapping tables.

The dmraid application is capable of creating these for a variety of ATARAID solutions (e.g. Highpoint, NVidia, Promise, VIA). It uses an abstracted representation of RAID devices and RAID sets internally to keep properties such as paths, sizes, offsets into devices and layout types (e.g. RAID0). RAID sets can be of arbitrary hierarchical depth in order to reflect more complex RAID configurations such as RAID10.

Because the various vendor specific metadata formats stored onto ATA devices by the ATARAID BIOS are all different, metadata format handlers are used to translate between the ondisk representation and the internal abstracted format.

The mapping tables which need to be loaded into device-mapper managed devices are derived from the internal abstracted format.

My talk will give a device-mapper architecture/feature overview and elaborate on the dmraid architecture and how it uses the device-mapper features to enable access to ATARAID devices.


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