Over the years I have been collating what Microsoft and the community as a whole deem to be best practice, over the coming months I will try to put them all together in one place for easy reference.
Disk Configuration
When configuring a dedicated domain controller I have never found an official best practice for the physical disk configurations but from speaking to peers and newsgroup harvests, the most popular configurations are:
6 Disks 3 Mirrored pairs
6 Disks 2 Mirrored C:\ and then 4 Raid 0+1 and two volumes created D:\ & E:\
6 Disks 2 Mirrored C:\ and then 4 Raid 5 and two volumes created D:\ & E:\
5 Disks 2 Mirrored C:\ and then 3 Raid 5 and two volumes created D:\ & E:\
C:\ System
D:\ NTDS.DIT\SYSVOL
E:\ Log Files
When building a Domain Controller to host Active Directory there are four areas of configuration that need to be taken into consideration.
System Files, AD Database, Sysvol and log files.
The recommendation is that in environments that have 1000 or more users accessing a domain controller, The AD database NTDS.DIT and SYSVOL should be separated from the Active Directory logs files (Microsoft recommended to leave the NTDS.DIT and SYSVOL on the same volume).
The volume hosting the NTDS.DIT is sized on the number of objects the DC will host, this is approximately 400MB for every 1000 users.
The SYSVOL should usually have at least 500MB of space allocated.
The log volume size should be the total size of the NTDS.DIT plus 20 percent or 500MB, whichever is greater.
In a healthy Active Directory environment there should not be too many log files as Active Directory logging is circular; once the log file is committed to Active Directory it is deleted.
So unless there are regularly huge number of changes to AD 2-3 gigabytes for the log volume should be ample.
This all being said and done with the size and capacity of the disks available today, even the smallest SCSI disks available should suite most corporates, what every configuration they utilise.
Source of information: http://technet.microsoft.com/en-us/library/cc757974.aspx
Comments please.