When planning a mailbox migration to Exchange Server 2007 you should consider the amount of transaction logging that will be generated by the move.  In low risk environments circular logging can be used to avoid disk space problems caused by the volume of transaction logs generated during bulk mailbox moves.

You can query the current state of circular logging on your storage groups with the Get-StorageGroup cmdlet.

[PS] C:\>Get-StorageGroup | fl name, circularloggingenabled

Name                   : SG1 Staff A-L
CircularLoggingEnabled : False

Name                   : SG2 Staff M-Z
CircularLoggingEnabled : False

Name                   : SG4 Public Folders
CircularLoggingEnabled : False

Name                   : SG3 Service Accounts
CircularLoggingEnabled : False

To enable circular logging use the Set-StorageGroup cmdlet.  You can enable circular logging on all storage groups together by piping a Get-StorageGroup command to Set-StorageGroup.

Get-StorageGroup | Set-StorageGroup -CircularLoggingEnabled $true

Get-StorageGroup will now reflect the change.

[PS] C:\>Get-StorageGroup | fl name, circularloggingenabled

Name                   : SG1 Staff A-L
CircularLoggingEnabled : True

Name                   : SG2 Staff M-Z
CircularLoggingEnabled : True

Name                   : SG4 Public Folders
CircularLoggingEnabled : True

Name                   : SG3 Service Accounts
CircularLoggingEnabled : True

Use Set-StorageGroup again to disable circular logging after your migration is complete.

Get-StorageGroup | Set-StorageGroup -CircularLoggingEnabled $false