Lucent Technologies 585-210-940 manual Mirrors, State databases

Introduction to Disk Mirroring	CentreVu CMS Release 3 Version 8 Disk-Mirrored Systems
Disk mirroring defined	3

	The total capacity of this concatenated metadevice is the combined
	capacities of the three drives. If each drive is 4 gigabytes, for example,
	the metadevice has an overall capacity of 12 gigabytes.
State databases	The Solstice DiskSuite software tracks which disk partitions belong to
	which metadevices with a state database. A state database stores
	information on disk about the state of your Solstice DiskSuite
	configuration.
	The state database consists of multiple copies of the basic database. The
	copies, referred to as state database replicas, ensure that the data in
	the database is always valid. Having multiple copies protects against
	data loss from single points-of-failure. The state database tracks the
	location and status of all state database replicas. Solstice DiskSuite
	cannot operate until you have created the state database and its replicas:
	the software must have an operating state database.

Mirrors	A mirror is a metadevice that can copy data from one metadevice to
	another. The metadevices containing the data are called submirrors.
	The process of copying the data between submirrors is called mirroring.
	Mirroring provides redundant copies of data. To a software application, a
	mirror looks just like a physical disk. The mirror accepts I/O requests and
	converts them into I/O requests for the submirrors. The submirrors in
	turn—being metadevices themselves—convert I/O requests from the
	mirror into I/O requests for the underlying physical disks.
	A mirror can be two-wayor three-way.A two-way mirror is a mirror with
	two submirrors; a three-way mirror has three submirrors. CMS supports
	only two-way mirrors. The illustration below shows a typical two-way
	mirror, d21, consisting of the submirrors d19 and d20.