RAID and Fault Tolerance

Referred to as a ‘mirrored volume’, in this configuration data is mirrored between 2 physical hard disks for the purpose of redundancy. In this configuration (which is very popular for the system or boot partitions) everything written to the first volume in the mirror set is also written to the second by the fault tolerant driver ftdisk.sys. In the event that the first volume in the mirror should fail, the data will still be accessible via the second disk. As with RAID 0 in Windows 2000, new implementations can only be done on dynamic disks. However, mirror sets from NT 4.0 can exist and function (and be repaired) if you performed an upgrade to Windows 2000. RAID 1 implementations do have a cost associated with them, using up twice as much disk space as would normally be necessary.


Referred to as a RAID 5 volume in Windows 2000, it is also commonly known as a stripe set with parity. In this configuration, which can utilize between 3 and 32 physical disks, not only data but also associated parity information is striped across the disks. Data and its associated parity information are always stored on different disks, which ensures that data can be rebuilt (and thus still accessed) in the event of a single disk failure. Again, new RAID 5 volumes can only be created on dynamic disks, although NT 4 stripe sets with parity can continue to exist if you performed an upgrade. As with stripe sets, the system and boot partitions cannot reside on a RAID 5 volume. Also note that there is an overhead associated with RAID 5 volumes – 1/X of the disk space will be used by parity information, where X is the number of disks in the set.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.