VERITAS Volume Manager 3.1 Migration Guide

Converting LVM to VxVM
General Information Regarding Conversion Speed
Chapter 2 59
have their LVM metadata copied. However, for the striped volume, 50
disks need to be checked and the LVM metadata for 50 disks must be
copied. 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 150 GB volume group consisting of 20 simple
logical volumes takes approximately 35-40 minutes to convert. In
contrast, the same volume group (150 Gb) consisting of mirrored
volumes that need to be synchronized can take 30-40 hours to
convert.
NOTE If you convert mirrored volumes, you must synchronize them in a
separate step.