VERITAS Volume Manager 5.0 Migration Guide (September 2006)

18 Converting LVM to VxVM
Converting LVM volume groups to VxVM disk groups
Volume group conversion limitations
There are certain LVM volume configurations that cannot be converted to VxVM. Some
of the reasons a conversion could fail are:
■ A volume group with insufficient space for metadata.
In the conversion of LVM to VxVM, the areas of the disks used to store LVM
metadata are overwritten with VxVM metadata. If the VxVM metadata that needs to
be written will not fit the space occupied by the LVM metadata, the group containing
the disk cannot be converted. If you have just enough space for the conversion, you
probably would want to have more space for future configuration changes.
Note: The most likely scenario in which a Volume Group cannot be converted,
because of insufficient private space, is when a large HP-UX system using “Extent
based Striping” is being used
■ A volume group containing the root volume.
vxvmconvert does not convert any volume group that contains a rootable volume,
identified by the presence of the LIF area as created by
mkboot(1M). Not only is the
current root volume off limits, but any volume that might be used as an alternate root
volume is rejected as well.
Note: You can use the vxcp_lvmroot(1M) command to create a VxVM root disk on a
spare physical disk from the contents of the existing LVM root disk. Similarly, you can
use the
vxres_lvmroot(1M) command to recreate an LVM root disk on a spare disk
from the contents of the VxVM root disk. For more information, see the section
“Rootability” in the “Administering Disks” chapter of the Veritas Volume Manager
Administrator’s Guide.
■ A volume group containing mirrors using the Mirror Write Cache feature for volume
consistency recovery.
Users should be aware that when converting mirrored LVM volumes to VxVM, some
of these volumes will likely have the Mirror Write Cache consistency recovery
method in force on the volume. The
vxvmconvert utility can convert these volumes,
but must use the Dirty Region Logging (DRL) feature to obtain the same level of
functionality. However, since Dirty Region Logging requires some user space to be
available for the log, a conversion could fail due to an MWC volume being full,
leaving no space for the DRL log. However it is very unlikely that this situation
would occur. Note that the MWC and DRL are used only when the system crashes or
is improperly shut down, to quickly bring all mirrors in the volume back into a
consistent state.
■ A volume group containing the /usr file system.