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237Creating 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 250 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 252 for more information.
See “Enabling FastResync on a volume” on page 292 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.
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.