VERITAS Volume Manager 3.5 Migration Guide (August 2002)

Chapter 2, Converting LVM to VxVM
Final 24 July 2002 General Information Regarding Conversion Speed
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Volume Manager: Initializing c5t4d0 as a converted LVM disk.
Volume Manager: Reconfiguration will be done without rebooting.
The Volume Manager is now reconfiguring (initialization phase)...
Volume Manager: Adding disk01 (c5t3d0) as a converted LVM disk.
Volume Manager: Adding disk02 (c5t4d0) as a converted LVM disk.
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 largerthe volumegroups,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 moremetadata to deal with. Theconverter has to readevery 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.