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

229Creating volumes
Types of volume layouts
Supported volume logs and maps
Veritas Volume Manager supports the use of several types of logs and maps with volumes:
■ FastResync Maps are used to perform quick and efficient resynchronization of
mirrors (see “FastResync” on page 66 for details). These maps are supported either in
memory (Non-Persistent FastResync), or on disk as part of a DCO volume (Persistent
FastResync). Two types of DCO volume are supported:
■ Version 0 DCO volumes only support Persistent FastResync for the traditional
third-mirror break-off type of volume snapshot. See “Version 0 DCO volume
layout” on page 69, and “Creating a volume with a version 0 DCO volume” on
page 241 for more information.
■ Version 20 DCO volumes, introduced in VxVM 4.0, support DRL logging (see
below) and Persistent FastResync for full-sized and space-optimized instant
volume snapshots. See “Version 20 DCO volume layout” on page 69, and
“Creating a volume with a version 20 DCO volume” on page 242 for more
information.
See “Enabling FastResync on a volume” on page 284 for information on how to
enable Persistent or Non-Persistent FastResync on a volume.
■ Dirty region logs allow the fast recovery of mirrored volumes after a system crash
(see “Dirty region logging” on page 60 for details). These logs are supported either as
DRL log plexes, or as part of a version 20 DCO volume. Refer to the following
sections for information on creating a volume on which DRL is enabled:
■ “Creating a volume with dirty region logging enabled” on page 243 for creating
a volume with DRL log plexes.
Layered Volume A volume constructed from other volumes. Non-layered volumes are
constructed by mapping their subdisks to VM disks. Layered volumes are
constructed by mapping their subdisks to underlying volumes (known as
storage volumes), and allow the creation of more complex forms of logical
layout. Examples of layered volumes are striped-mirror and concatenated-
mirror volumes.
See “Layered volumes” on page 51.
A striped-mirror volume is created by configuring several mirrored volumes
as the columns of a striped volume. This layout offers the same benefits as a
non-layered mirrored-stripe volume. In addition it provides faster recovery as
the failure of single disk does not force an entire striped plex offline.
See “Mirroring plus striping (striped-mirror, RAID-1+0 or RAID-10)” on
page 43.
A concatenated-mirror volume is created by concatenating several mirrored
volumes. This provides faster recovery as the failure of a single disk does not
force the entire mirror offline.