For logging and master devices - Place logging devices and master device that belong to the same trans metadevice on separate drives and controllers.
For trans metadevices and shared logging devices - Trans metadevices can share metadevice logging devices. But file systems with the heaviest loads should have separate logs.
For small file systems - Small file systems with mostly read operations probably do not need to be logged.
For mirroring logging devices - Mirror all logging devices whenever possible. Losing the data in a log because of device errors can leave a file system in an inconsistent state which fsck(1M) may not be able to repair without user intervention.
Larger logging devices result in greater concurrency.