The log files directory requires varying amounts of I/O depending on the level of logging that is enabled. The I/O on the logging directory, unlike all of the other high I/O requirements of the Message Store, is asynchronous. For typical deployment scenarios, do not dedicate an entire Logical Unit Number (LUN) for logging. For very large store deployments, or environments where significant logging is required, a dedicated LUN is in order.
In almost all environments, you need to protect the Message Store from loss of data. The level of loss and continuous availability that is necessary varies from simple disk protection such as RAID5, to mirroring, to routine backup, to real time replication of data, to a remote data center. Data protection also varies from the need for Automatic System Recovery (ASR) capable machines, to local HA capabilities, to automated remote site failover. These decisions impact the amount of hardware and support staff required to provide service.