admin-guide/device-mapper/switch.rst

2 dm-switch
5 The device-mapper switch target creates a device that supports an
6 arbitrary mapping of fixed-size regions of I/O across a fixed set of
11 number of fixed-sized address regions but there is no simple pattern
13 dm-stripe.
16 ----------
19 frameless architecture.  In this architecture, the storage group
24 The storage group exposes a single target discovery portal, no matter
34 the storage group and initiators.  In a multipathing configuration, it
42 A device-mapper table already lets you map different regions of a
48 Using this device-mapper switch target we can now build a two-layer
51     Upper Tier - Determine which array member the I/O should be sent to.
52     Lower Tier - Load balance amongst paths to a particular member.
56 the array member in one priority group, and leverages existing path
58 non-preferred priority group containing paths to other array members for
61 The upper tier consists of a single dm-switch device.  This device uses
64 use 4 bits for each address range in a 16 member group (which is very
66 b-tree can achieve.
76 	    The number of 512-byte sectors in a region. Each region can be redirected
88 	    of 512-byte sectors). This number is added to the sector number when
94 set_region_mappings <index>:<path_nr> [<index>]:<path_nr> [<index>]:<path_nr>...
99 <index>
101     If index is omitted, the next region (previous index + 1) is used.
105     The path number in the range 0 ... (<num_paths> - 1).
126     dmsetup create switch --table "0 `blockdev --getsz /dev/vg1/switch0`