- W2K OS: use two physical disks mirrored (get OS pagefile on separate drive)
- AD database store NTDS.dit : use RAID5 of appropriate size for your enterprise
- AD log files : use two physical disks mirrored
The ESE engine can use the transaction records in the log files to recreate the database. The transaction logs are also used by ESE to verify that a restored datastore is consistent with the tranaction records. The log files for AD can be either sequential or circular logs. Circular logs overwrite transactions at specific intervals wheras sequential logs never overwrite transactions. Depending on log size and activity, circular logs may or may not have enough data should the datastore need recovery. I hear you now, if the sequential logs are never overwritten, what keeps the logs from consuming all available DASD? The Active Directory's garbage collection process: log files whose transaction records have been committed to the datastore are deleted. The garbage collection process deletes obsolete log files every 12 hours by default.
The default is sequential logs. They are safer. I know circular log files are more predictable in maximum space consumed, but when the sh*t hits the fan, critical records may no longer be in the sequential log files. Hard drive space is cheap. Get a couple of large disks and mirror them and leave the logs files as the default sequential format.