Network+
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Networking Fundamentals
network attached
storage (NAS)
a device or collec-
tion of devices that
provide storage for
network data.
storage area
network (SAN)
a separate, high-
speed network that
provides a storage
facility for one or
more networks.
RAID 0/1
RAID 0/1, or RAID 10, uses multiple RAID 1 (mirroring) disk systems. It also
incorporates disk striping across each of the mirrored disk sets. When compared
to RAID 1, this system provides better fault tolerance because data is duplicated
on multiple mirrored disk sets. It also provides relatively fast data-transfer speeds
by striping data across the mirrored disk sets.
RAID 0/5
RAID 0/5, or RAID 50, uses several RAID 5 (block striping with parity)
sets and combines them with RAID 0 (disk striping). It provides increased fault
tolerance when compared to a RAID 5 system.
RAID 6
RAID 6 is similar to RAID 5 in that it distributes parity across all drives, except
RAID 6 uses a second set of parity. This technique is referred to as dual parity. The
additional parity set allows for protection from simultaneous two-disk failure. Since
two simultaneous disk failures are rarely encountered, RAID 6 is not commonly used.
Network+ Note
Pay particular attention to RAID 0, 1, and 5. These systems are the
most commonly used and are the ones most likely to be covered on the
Network+ Certifi cation exam.
External Storage Systems
Data is often stored separately from a server. There are network devices that
serve specifi cally as storage containers for network data. These devices are typically
called network attached storage (NAS). There are also facilities external to the local
area network that provide data storage. These devices are typically called storage
area network (SAN). This section discusses both types of storage systems.
Network-Attached Storage (NAS)
Network attached storage (NAS) is a device or collection of devices that
provide storage for network data. Network attached storage units are typically
composed of disk arrays or tape arrays. The fi le systems used on the disk array
and fi le array do not typically match the fi le system used by network clients or
servers. The fi le systems are proprietary and are made to facilitate access speed
and data integrity.
This is how data on a NAS device is accessed. A client requesting data makes
a request to the fi le server. The fi le server in turn makes a request to the NAS
device. The NAS device retrieves the data and sends it to the fi le server. The fi le
server, in turn, sends the data to the client. See Figure 9-24.
Storage Area Network (SAN)
A storage area network (SAN) is a separate, high-speed network that
provides a storage facility for one or more networks. Typically, a SAN uses a
high-speed access media such as Fibre Channel. See Figure 9-25. Fibre Channel is
discussed in the next section of the chapter.