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
Compatibility of disk groups between platforms
For disk groups that support the Cross-platform Data Sharing (CDS) feature, the upper limit on the minor number range is restricted on AIX, HP-UX, Linux (with a 2.6 or later kernel) and Solaris to 65,535 to ensure portability between these operating systems.
On a Linux platform with a pre-2.6 kernel, the number of minor numbers per major number is limited to 256 with a base of 0. This has the effect of limiting the number of volumes and disks that can be supported system-wide to a smaller value than is allowed on other operating system platforms. The number of disks that are supported by a pre-2.6 Linux kernel is typically limited to a few hundred. With the extended major numbering scheme that was implemented in VxVM 4.0 on Linux, a maximum of 4079 volumes could be configured, provided that a contiguous block of 15 extended major numbers was available.
VxVM 4.1 and later releases run on a 2.6 version Linux kernel, which increases the number of minor devices that are configurable from 256 to 65,536 per major device number. This allows a large number of volumes and disk devices to be configured on a system. The theoretical limit on the number of DMP and volume devices that can be configured on such a system are 65,536 and 1,048,576 respectively. However, in practice, the number of VxVM devices that can be configured in a single disk group is limited by the size of the private region.
When a CDS-compatible disk group is imported on a Linux system with a pre-2.6 kernel, VxVM attempts to reassign the minor numbers of the volumes, and fails if this is not possible.
To help ensure that a CDS-compatible disk group is portable between operating systems, including Linux with a pre-2.6 kernel, use the following command to set the maxdev attribute on the disk group:
# vxdg -g diskgroup set maxdev=4079
Note:
Such a disk group may still not be importable by VxVM 4.0 on Linux with a pre-2.6 kernel if it would increase the number of minor numbers on the system that are assigned to volumes to more than 4079, or if the number of available extended major numbers is smaller than 15.
You can use the following command to discover the maximum number of volumes that are supported by VxVM on a Linux host:
# cat /proc/sys/vxvm/vxio/vol_max_volumes 4079
See the vxdg(1M) manual page.