менеджер логических томов для объединения нескольких физических дисковых устройств в логический модуль (LVM RAID)
Описание (Description)
lvm(8) RAID is a way to create a Logical Volume (LV) that uses
multiple physical devices to improve performance or tolerate
device failures. In LVM, the physical devices are Physical
Volumes (PVs) in a single Volume Group (VG).
How LV data blocks are placed onto PVs is determined by the RAID
level. RAID levels are commonly referred to as 'raid' followed
by a number, e.g. raid1, raid5 or raid6. Selecting a RAID level
involves making tradeoffs among: physical device requirements,
fault tolerance, and performance. A description of the RAID
levels can be found at
www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
LVM RAID uses both Device Mapper (DM) and Multiple Device (MD)
drivers from the Linux kernel. DM is used to create and manage
visible LVM devices, and MD is used to place data on physical
devices.
LVM creates hidden LVs (dm devices) layered between the visible
LV and physical devices. LVs in the middle layers are called sub
LVs. For LVM raid, a sub LV pair to store data and metadata
(raid superblock and write intent bitmap) is created per raid
image/leg (see lvs command examples below).
