Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

19Understanding Veritas Volume Manager
VxVM and the operating system
VxVM and the operating system
VxVM operates as a subsystem between your operating system and your data
management systems, such as file systems and database management systems. VxVM is
tightly coupled with the operating system. Before a disk can be brought under VxVM
control, the disk must be accessible through the operating system device interface. VxVM
is layered on top of the operating system interface services, and is dependent upon how the
operating system accesses physical disks.
VxVM is dependent upon the operating system for the following functionality:
■ operating system (disk) devices
■ device handles
■ VxVM dynamic multipathing (DMP) metadevice
This guide introduces you to the VxVM commands which are used to carry out the tasks
associated with VxVM objects. These commands are described on the relevant manual
pages and in the chapters of this guide where VxVM tasks are described.
VxVM relies on the following constantly-running daemons and kernel threads for its
operation:
■ vxconfigd—The VxVM configuration daemon maintains disk and group
configurations and communicates configuration changes to the kernel, and modifies
configuration information stored on disks.
■ vxiod—VxVM I/O kernel threads provide extended I/O operations without blocking
calling processes. By default, 16 I/O threads are started at boot time, and at least one
I/O thread must continue to run at all times.
■ vxrelocd—The hot-relocation daemon monitors VxVM for events that affect
redundancy, and performs hot-relocation to restore redundancy.
How data is stored
There are several methods used to store data on physical disks. These methods organize
data on the disk so the data can be stored and retrieved efficiently. The basic method of
disk organization is called formatting. Formatting prepares the hard disk so that files can
be written to and retrieved from the disk by using a prearranged storage pattern.
Hard disks are formatted, and information stored, using two methods: physical-storage
layout and logical-storage layout. VxVM uses the logical-storage layout method. The
types of storage layout supported by VxVM are introduced in this chapter.