Creating volumes

 

237

 

 

 

Types of volume layouts

 

 

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.

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.