Veritas Volume Manager 5.0 Migration Guide, HP-UX 11i v3, First Edition, May 2008

44 Converting LVM to VxVM
General information regarding conversion speed
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General information regarding conversion speed
The speed of the process of converting an existing LVM volume group to a
similar VxVM disk group is largely dependent upon the size of the volume group
being converted, as well as on the complexity of the volumes within that volume
group.
Factors affecting conversion speed include:
■ Size of volume groups. The larger the volume groups, the larger the LVM
metadata on each disk. A copy must be made of the LVM metadata for each
physical disk. Some areas are greater than 2MB; therefore, a 50-disk volume
group requires 50 2MB reads and writes (i.e., 100 large I/Os) to complete.
■ Individual size of a logical volume in a volume group, and the complexity of
the logical volume layout. For example, for a system with 50 9GB drives, a
simple 50GB logical volume of the first 5 1/2 disks can be created. But a
50GB striped logical volume that takes the first 1GB of all 50 disks can also
be created. The first and simple logical volume takes less time to convert
than the striped volume. However, for the striped volume, 50 disks need to
be checked. Also, the complexity of reproducing the VxVM commands to set
up the striped volumes requires more VxVM commands to be generated to
represent more smaller sub-disks representing the same amount of space.
Another factor in converting stripes is that stripes create more work for the
converter. In some cases, stripes require 1GB volume, although only the
metadata is being changed. In other cases, where there are more physical
disks in one volume than another, there is more metadata to deal with. The
converter has to read every physical extent map to ensure there are no
holes in the volume; if holes are found, the converter maps around them.
■ Number of volumes. While it takes longer to convert one 64GB volume than
one 2GB volume, it also takes longer to convert 64 1GB volumes than one
64GB volume, providing that the volumes are of similar type.
■ Mirrored volumes. Mirrored volumes typically do not take more time to
convert than simple volumes. Volumes that are mirrored and striped at the
same time would take longer, but LVM currently does not allow this.
Currently, after conversion, mirrored volumes are not automatically
synchronized because a large mirror could take hours to complete.
For example, in tests, a 150GB volume group consisting of 20 simple logical
volumes takes approximately 35-40 minutes to convert. In contrast, the