Veritas™ Volume Manager Administrator's Guide
- Understanding Veritas Volume Manager
- VxVM and the operating system
- How VxVM handles storage management
- Volume layouts in VxVM
- Online relayout
- Volume resynchronization
- Dirty region logging
- Volume snapshots
- FastResync
- Provisioning new usable storage
- Administering disks
- Disk devices
- Discovering and configuring newly added disk devices
- Discovering disks and dynamically adding disk arrays
- How to administer the Device Discovery Layer
- Changing the disk-naming scheme
- Adding a disk to VxVM
- Rootability
- Displaying disk information
- Removing disks
- Removing and replacing disks
- Administering Dynamic Multi-Pathing
- How DMP works
- Administering DMP using vxdmpadm
- Gathering and displaying I/O statistics
- Specifying the I/O policy
- Online dynamic reconfiguration
- Reconfiguring a LUN online that is under DMP control
- Creating and administering disk groups
- About disk groups
- Displaying disk group information
- Creating a disk group
- Importing a disk group
- Moving disk groups between systems
- Handling cloned disks with duplicated identifiers
- Handling conflicting configuration copies
- Reorganizing the contents of disk groups
- Destroying a disk group
- Creating and administering subdisks and plexes
- Displaying plex information
- Reattaching plexes
- Creating volumes
- Types of volume layouts
- Creating a volume
- Using vxassist
- Creating a volume on specific disks
- Creating a mirrored volume
- Creating a striped volume
- Creating a volume using vxmake
- Initializing and starting a volume
- Using rules and persistent attributes to make volume allocation more efficient
- Administering volumes
- Displaying volume information
- Monitoring and controlling tasks
- Reclamation of storage on thin reclamation arrays
- Stopping a volume
- Resizing a volume
- Adding a mirror to a volume
- Preparing a volume for DRL and instant snapshots
- Adding traditional DRL logging to a mirrored volume
- Enabling FastResync on a volume
- Performing online relayout
- Adding a RAID-5 log
- Creating and administering volume sets
- Configuring off-host processing
- Administering hot-relocation
- How hot-relocation works
- Moving relocated subdisks
- Administering cluster functionality (CVM)
- Overview of clustering
- Multiple host failover configurations
- CVM initialization and configuration
- Dirty region logging in cluster environments
- Administering VxVM in cluster environments
- Changing the CVM master manually
- Importing disk groups as shared
- Administering sites and remote mirrors
- About sites and remote mirrors
- Fire drill - testing the configuration
- Changing the site name
- Administering the Remote Mirror configuration
- Failure and recovery scenarios
- Performance monitoring and tuning
- Appendix A. Using Veritas Volume Manager commands
- Appendix B. Configuring Veritas Volume Manager
How online relayout works
Online relayout allows you to change the storage layouts that you have already created in place without disturbing data access. You can change the performance characteristics of a particular layout to suit your changed requirements. You can transform one layout to another by invoking a single command.
For example, if a striped layout with a 128KB stripe unit size is not providing optimal performance, you can use relayout to change the stripe unit size.
File systems mounted on the volumes do not need to be unmounted to achieve this transformation provided that the file system (such as Veritas File System) supports online shrink and grow operations.
Online relayout reuses the existing storage space and has space allocation policies to address the needs of the new layout. The layout transformation process converts a given volume to the destination layout by using minimal temporary space that is available in the disk group.
The transformation is done by moving one portion of data at a time in the source layout to the destination layout. Data is copied from the source volume to the temporary area, and data is removed from the source volume storage area in portions. The source volume storage area is then transformed to the new layout, and the data saved in the temporary area is written back to the new layout. This operation is repeated until all the storage and data in the source volume has been transformed to the new layout.
The default size of the temporary area used during the relayout depends on the size of the volume and the type of relayout. For volumes larger than 50MB, the amount of temporary space that is required is usually 10% of the size of the volume, from a minimum of 50MB up to a maximum of 1GB. For volumes smaller than 50MB, the temporary space required is the same as the size of the volume.
The following error message displays the number of blocks required if there is insufficient free space available in the disk group for the temporary area:
tmpsize too small to perform this relayout (nblks minimum required)
You can override the default size used for the temporary area by using the tmpsize attribute to vxassist.
See the vxassist(1M) manual page.
As well as the temporary area, space is required for a temporary intermediate volume when increasing the column length of a striped volume. The amount of space required is the difference between the column lengths of the target and source volumes. For example, 20GB of temporary additional space is required to relayout a 150GB striped volume with 5 columns of length 30GB as 3 columns of length 50GB. In some cases, the amount of temporary space that is required is relatively large. For example, a relayout of a 150GB striped volume with 5 columns as a concatenated volume (with effectively one column) requires 120GB of space for the intermediate volume.
Additional permanent disk space may be required for the destination volumes, depending on the type of relayout that you are performing. This may happen, for example, if you change the number of columns in a striped volume.
Figure: Example of decreasing the number of columns in a volume shows how decreasing the number of columns can require disks to be added to a volume.
Note that the size of the volume remains the same but an extra disk is needed to extend one of the columns.
The following are examples of operations that you can perform using online relayout:
Remove parity from a RAID-5 volume to change it to a concatenated, striped, or layered volume.
Figure: Example of relayout of a RAID-5 volume to a striped volume shows an example of applying relayout a RAID-5 volume.
Note that removing parity decreases the overall storage space that the volume requires.
Add parity to a volume to change it to a RAID-5 volume.
Figure: Example of relayout of a concatenated volume to a RAID-5 volume shows an example.
Note that adding parity increases the overall storage space that the volume requires.
Change the number of columns in a volume.
Figure: Example of increasing the number of columns in a volume shows an example of changing the number of columns.
Note that the length of the columns is reduced to conserve the size of the volume.
Change the column stripe width in a volume.
Figure: Example of increasing the stripe width for the columns in a volume shows an example of changing the column stripe width.