Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

234 Creating volumes

Discovering the maximum size of a volume

To find out how large a volume you can create within a disk group, use the following form

of the

vxassist command:

# vxassist [-g diskgroup] maxsize layout=layout [attributes]

For example, to discover the maximum size RAID-5 volume with 5 columns and 2 logs

that you can create within the disk group, dgrp, enter the following command:

# vxassist -g dgrp maxsize layout=raid5 nlog=2

You can use storage attributes if you want to restrict the disks that vxassist uses when

creating volumes. See “Creating a volume on specific disks” on page 235 for more

information.

Note: The maximum size of a VxVM volume that you can create is 256TB.

Disk group alignment constraints on volumes

Certain constraints apply to the length of volumes and to the numeric values of size

attributes that apply to volumes. If a volume is created in a disk group that is compatible

with the Cross-platform Data Sharing (CDS) feature, the volume’s length and the values

of volume attributes that define the sizes of objects such as logs or stripe units, must be an

integer multiple of the alignment value of 8 blocks (8 kilobytes). If the disk group is not

compatible with the CDS feature, the volume’s length and attribute size values must be

multiples of 1 block (1kilobyte).

To discover the value in blocks of the alignment that is set on a disk group, use this

command:

# vxprint -g diskgroup -G -F %align

By default, vxassist automatically rounds up the volume size and attribute size values to

a multiple of the alignment value. (This is equivalent to specifying the attribute

dgalign_checking=round as an additional argument to the

vxassist command.)

If you specify the attribute dgalign_checking=strict to

vxassist, the command

fails with an error if you specify a volume length or attribute size value that is not a

multiple of the alignment value for the disk group.

Creating a volume on any disk

By default, the vxassist make command creates a concatenated volume that uses one or

more sections of disk space. On a fragmented disk, this allows you to put together a

volume larger than any individual section of free disk space available.