VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 1, Understanding VERITAS Volume Manager
Volume Layouts in VxVM
15
Concatenation and Spanning
Concatenation maps data in a linear manner onto one or more subdisks in a plex. To access
all of the data in a concatenated plex sequentially, data is first accessed in the first subdisk
from beginning to end. Data is then accessed in the remaining subdisks sequentially from
beginning to end, until the end of the last subdisk.
The subdisks in a concatenated plex do not have to be physically contiguous and can
belong to more than one VM disk. Concatenation using subdisks that reside on more than
one VM disk is called spanning.
The figure, “Example of Concatenation”, shows concatenation with one subdisk.
Example of Concatenation
You can use concatenation with multiple subdisks when there is insufficient contiguous
space for the plex on any one disk. This form of concatenation can be used for load
balancing between disks, and for head movement optimization on a particular disk. See
the figure, “Example of a Volume in a Concatenated Configuration.”
Example of a Volume in a Concatenated Configuration
VM Disk
Physical Disk
Plex
B = Block of data
disk01
disk01-01
disk01-01
B1
B2
B3
B4
devname
VM Disk
Physical Disk
Subdisks
disk01-01
disk01-03
disk01-02
Concatenated
devname
disk01
disk01-03
Volume
vol01-01
vol01
Plex
disk01-01
disk01-02
vol01-01
disk01-03
disk01-01
disk01-02
disk01-02
disk01-01
disk01-03