Tech Tip
386
Networking Fundamentals
disk mirroring
the act of writing the
same information to
two hard disk drives
at the same time.
duplexing
the technique
of placing each
mirrored hard drive
on a separate hard
disk drive controller.
When implementing a RAID system in a Microsoft Windows operating system, all drives
must be dynamic disk.
See Figure 9-19 for a list of RAID levels and a short description of each. The
following section looks at each RAID level in detail.
RAID 0
RAID 0 uses disk striping across a group of independent hard disk drives,
Figure 9-20. This technique increases data fl ow but provides no fault tolerance. If
one hard disk drive fails, all data is lost and cannot be reconstructed. This RAID
level is most useful when speed is important, not fault tolerance.
RAID 1
RAID 1 uses the technique of disk mirroring. Disk mirroring is the act of
writing the same information to two hard disk drives at the same time, Figure 9-21.
Each of the two hard disk drives contains the same data. If one hard disk drive
fails, a copy exists on the other hard disk drive.
Another form of RAID 1 is duplexing. Duplexing is the technique of placing
each mirrored hard drive on a separate hard disk drive controller. Duplexing
adds another level of fault tolerance. If one hard disk drive controller fails, the
other is still operable. Mirroring contains the risk of the hard disk drive controller
failing and causing both hard disk drives to fail. RAID 1 provides data protection
at the cost of speed when compared to RAID 0. When there is a small demand for
disk read/writes, RAID 1 is an appropriate technique.
Figure 9-19.
RAID levels.
RAID Level Description
RAID 0 Striping.
RAID 1 Mirroring or duplexing.
RAID 2 Error checking code (ECC).
RAID 3 Byte-level striping with parity.
RAID 4 Block-level striping with parity.
RAID 5 Block-level striping with distributed parity.
RAID 6 Dual parity.
RAID 0/1 or 10 Disk mirroring with striping.
RAID 0/5 or 50 Block striping with parity and striping.
Figure 9-20.
RAID 0 divides
data and writes it to
multiple drives. It
provides excellent
data transfer rates
but no data loss
protection.
110100100101010101010101001010010101010
110100 100101 010101