Converting a Non-CDS Disk Group to a CDS Disk Group

Use the CDS conversion utility (vxcdsconvert) to make a VxVM non-CDS disk group (DG) portable between different operating systems that are running versions of VxVM with the CDS feature. This allows existing data to be made shareable in a CDS environment.

CDS provides the alignment and group keywords for disk group conversion:

• Use the alignment keyword to specify alignment conversion. In this case, disks are not converted, and an object relayout is performed on the disk group. A successful completion results in an 8K-aligned disk group. You might consider this option, rather than converting the entire disk group, if you want to reduce the amount of work to be done for a later full conversion to CDS disk group.
• Use the group keyword to specify group conversion. This implies alldisk, and will perform that function prior to object relayout. All the non-CDS disks in the disk group are converted.

In addition, you can use the -o novolstop option to perform the conversion on-line (that is, while use of the disk group continues). However, for a group conversion, this may greatly increase the amount of time (and work) required for conversion.

Alternatively, stop the application, and perform the conversion off-line. This requires minimal offline time.

Note the following:

• The disk group must be in pristine condition. That is:
• It has no dissociated or disabled objects.
• No sparse plexes are present.
• There are no volumes requiring recovery or having pending snapshot operations.
• There are no objects in an error state.
• Stopped (but startable) volumes will be started, for the duration of the conversion only.
• Conversion has the following side effects:
• Any objects created with layout=diskalign can no longer be disk aligned.
• Encapsulated disks may lose the ability to be unencapsulated.
• Fine performance tuning may be lost as data may have migrated (and even migrated to different disks).

Please refer to the vxcdsconvert(1M) manual page for information on options, attributes, and keywords.

Notes

• A non-CDS disk group will be upgraded (using the vxdg upgrade command). Also, if the disk group was originally created by the conversion of an LVM Volume Group (VG), then rolling back to the original LVM VG is not an option. If you decide to go through with the conversion, the rollback records for the disk group will be removed, so that an accidental rollback to an LVM VG cannot be done.
• If the non-CDS disk group has one or more disks that are not CDS disks, these disks are converted to CDS disks. If you do not want one or more of these disks to be converted, you need to move them out of the disk group (for example, using vxdg move or split) prior to invoking the vxcdsconvert group command.
• If the non-CDS disk group does not have a CDS-compatible disk group alignment, the objects need to go through relayout, so they have a CDS-compatible alignment.
• Unless the novolstop option is specified, applications using disks which require format conversion must be terminated for the duration of the disk conversion process.
• Use of the novolstop option for the disk conversion piece may add a large amount of work, as objects may need to be evacuated and then unrelocated back.

Examples

• Check if the disk group mydg and all its disks can be made portable, using the command:

# vxcdsconvert -g mydg -A group
• Make the disk group mydg and all its disks portable while its volumes are still online. You can avoid using the novolstop option during disk conversion by using the following sequence of commands:
• Stop all applications that are using volumes on the disks requiring format conversion.
• Enter the command:

   # vxcdsconvert -g mydg alldisks
• Restart applications.
• Enter the command:

   # vxcdsconvert -g mydg group
• Make the disk group, anodg, and all its disks, portable while its volumes are still online, and allow subdisks to be evacuated to disks anodg11 through anodg14 if required:

# vxcdsconvert -g anodg -o novolstop group \
move_subdisks_ok=yes evac_subdisks_ok=yes \
evac_disk_list=anodg11,anodg12,anodg13,anodg14