Description

vxassist mirror command  in Veritas Volume Manager (VxVM) will create DCO log volume on thin lun by default.

In VxVM 6.0 by default, mirror volumes on thin provisioning LUNs are created with an DCO log volume. This is applicable even if any of the other LUNs in the diskgroup that is not used for the volume has thin capable LUNs.

The purpose of adding DCO for thin lun by default is to prevent wasting disk space with mirror full resync (THIN LUNs becoming THICK).  Another important thing is even though DCO is added, there will be no activity unless detached-plex/snapshots are created on volume.  So there should not be any overhead in I/O.  Veritas does not recommend to create mirror without DCO log.

But if still want to create mirror volume without dco, below option can be used: 

#  vxassist -g mirror logtype=none

or

add "logtype=none" in /etc/default/vxassist file to make it as default option.

Applies To

VxVM 6.0 and above with thin LUNs in the diskgroup