The purpose of the MWC
The purpose of the MWC is to guarantee the consistency of the mirrored logical volumes in case of a crash.
The consistency of the file systems is guaranteed by the JFS logs.
The purpose of the passive method
Passive MWC reduces the problem of having to update the MWC log on the disk.
This method logs that the logical volume has been opened but does not log writes.
If the system crashes, then LVM starts a forced synchronization of the entire logical volume when the system restarts.
Data consistency exists for reads that occur during the synchronization so that applications can start using the data as soon as the volume group is varied on.
Support for the passive option
The passive method is only available on volume groups with the big volume group format since they have space to store a flag for each logical volume.
Big volume groups allow up to 512 logical volumes and 128 physical volumes per volume group.
MWC settings
The following syntax is used with either the mklv or chlv command to set MWC
options:
mklv -w y|a|p|n
chlv -w y|a|p|n
Following is a description of the MWC arguments: