Shrinking a volume using the CLI

You can reduce the size of a compressed or uncompressed volume by using the command-line interface (CLI).

About this task

Volumes can be reduced in size, if it is necessary. You can make a target or auxiliary volume the same size as the source or master volume when you create FlashCopy® mappings, Metro Mirror relationships, or Global Mirror relationships. However, if the volume contains data, do not shrink the size of the disk. If the volume is being formatted, the system cannot shrink the volume. After it is formatted, you can shrink the volume.

Attention:
  1. It is difficult to anticipate how an operating system or file system uses the capacity in a volume. When you shrink a volume, capacity is removed from the end of the disk, whether or not that capacity is in use. Even if a volume has free capacity, do not assume that only unused capacity is removed when you shrink a volume.
  2. If the volume contains data that is being used, do not attempt under any circumstances to shrink a volume without first backing up your data.
  3. For performance reasons, some operating systems or file systems use the outer edge of the disk.
  4. Do not shrink Global Mirror volumes or Global Mirror change volumes or run recovervdisk.

You can use the shrinkvdisksize command to shrink the physical capacity that is allocated to the particular volume by the specified amount. You can also shrink the virtual capacity of a thin-provisioned volume without altering the physical capacity that is assigned to the volume.

You cannot shrink the capacity of any volume in a Global Mirror with change volumes relationship or in a HyperSwap® relationship.

You can shrink the capacity of volumes in Metro Mirror and Global Mirror relationships that are in consistent_synchronized state. You cannot shrink the following types of volumes:
  • Volumes in HyperSwap relationships or in Global Mirror relationships that are operating in cycling mode.
  • Volumes in relationships where a change volume is configured.
  • Mirrored volumes that have at least one fully allocated copy.

You must shrink both volumes in a relationship to maintain full operation of the system. Shrink the primary volume by the required capacity, and then shrink the secondary volume.

Procedure

Complete the following steps to shrink a volume:

  1. Validate that the volume is not mapped to any host objects. If the volume is mapped, data is displayed.
  2. You can determine the exact capacity of the source or master volume. Issue the following command:
    lsvdisk -bytes vdisk_name
  3. Shrink the volume by the required amount. Enter the following command, where size_change indicates the size reduction for the volume in the specified units and vdisk_name is the volume that you are shrinking. 
    shrinkvdisksize -size size_change -unit
b | kb | mb | gb | tb | pb vdisk_name