Information Technology Reference
In-Depth Information
Network Volumes
As you've seen so far in this chapter, most computer storage is directly
attached to the individual computer. This is known as local storage, or
direct-attached storage (DAS)
. However, computers can also use a
network to access storage that's not physically nearby.
direct-attached storage (DAS)
Storage
that is directly connected to the computer that
accesses it.
Network storage can enable multiple users to access the same up-to-
the-minute information simultaneously. For example, in a retail business
with multiple checkout areas, all the checkout computers access a com-
mon database containing the item prices so that when the price of an
item changes, all cashiers immediately have that information available. On
a smaller scale, a family could store its movie and music collection on one
computer, which then can share the collection with all the other com-
puters in the household via the family's wireless network. Storage that is
available via a network is called
network-attached storage (NAS)
.
network-attached storage (NAS)
Storage
that is accessed via a network.
Generically speaking, network-attached storage can be a volume on a file
server in a business network or a shared folder on an individual's personal
computer. However, the term is most often applied to a
NAS appliance
,
which is a specialized computing device built specifically for network file
sharing. The appliance connects directly into the network, and can be
remotely configured from any computer, so it doesn't need its own input
or output devices. NAS appliances are available for consumers as well as
businesses; for example, you could connect an inexpensive NAS appliance
to your home network to provide everyone in your family with always-on
access to shared files.
NAS appliance
A specialized device that pro-
vides storage space to network users.
Some large companies employ
storage-area networks (SANs)
to make
central access to large amounts of data simple. A SAN logically combines
the contents of multiple remote storage devices so that each individual com-
puter connected to the SAN sees that storage pool as a single local drive.
storage-area network (SAN)
A distributed
storage system that appears to each individual
computer as a local volume on that computer.
When it is essential that data be kept safe and readily available, some
companies store that data on a
redundant array of inexpensive disks
(RAID)
. There are several types of RAID systems, and each type offers
improvements over a single disk drive in performance, in data safety, or
in both. Usually, when you store data on a disk you write to one disk at a
time. RAID systems have the capability to spread the data across multiple
drives so each physical disk contains part of the data; this is called
striping
.
For example, RAID0 stripes data across multiple physical disks to improve
the speed at which data is accessed, and RAID1 mirrors the contents of a
physical disk on another identical disk so that the data is always available
even if the original disk fails. RAID5 combines the striping from RAID0
with a data storage method that enables the RAID unit to reconstruct lost
data on any of the physical disks in the event of a disk failure.
redundant array of inexpensive disks
(RAID)
A multi-disk storage system that opti-
mizes performance, data safety, or both, depend-
ing on the type.
striping
Spreading the data across multiple
drives to improve performance or protect the data.
Cloud-Based Storage
A
cloud
is a secure computing environment consisting of a set of
remote servers that users access via the Internet. A cloud can include
applications, communication with other users, and storage space (
cloud
storage
).
cloud
A secure computing environment accessed
via the Internet.
cloud storage
Storage that is accessed from a
cloud environment.
