Database Reference
In-Depth Information
A large number of storage systems emerge to meet the demands of big data.
Existing storage technologies can be classified as DAS (Direct Attached Storage)
and network storage, while network storage can be further classified into NAS
(Network Attached Storage) and SAN (Storage Area Network).
In DAS, disc drives are directly connected with servers. Storage is a peripheral
equipment, while, data management servers and all kinds of application software are
matched with storage sub-systems (this way, I/O may stress system bandwidths).
DAS applies to a few server environments but, when the storage capacity is
increased, the efficiency of storage supply will be quite low and the upgradeability
and expandability will be greatly limited. In case of server abnormality, data could
not be acquired and stored resources and data could not be shared. DAS is mainly
used in personal computers and small-sized servers, which only support such
applications requiring low storage capacities and does not directly support multi-
computer shared storage. Tap drivers and RAID (redundant array of independent
disks) are classic DAS equipments.
Network storage is to utilize the original network or a specially designed storage
network to provide users with a uniform information access and sharing services of
information systems. Network storage equipment includes special data exchange
equipments, disk array, tap library, and other storage media, as well as special
storage software. It is characterized with mass data storage, limited data sharing, full
utilization of data mining and information, data reliability, data backup and safety,
as well as simplified and unified data management. In addition, network storage
features very strong expandability, so as to provide information transmission rates
suited for large data volume.
NAS is actually an auxiliary storage equipment of a network. It is directly
connected to a network through a hub or switch, communicating with the TCP/IP
protocol. NAS is geared to message passing, and transmits data in the form of files.
NAS has two prominent features. First, on physical connection, it directly connects
the storage equipment to a network and then hangs the storage at the rear end of
a server, thus avoiding the I/O burden at the server. Second, technically, it reduces
the movements of the disk actuator arm and thus reduces R/W delay. However,
the structure of NAS shows that it is still a traditional server storage equipment in
essence.
SAN focuses on data storage with a flexible network topology and high-speed
optical fiber connections. It allows multipath data switching among any internal
nodes. Data storage management is located in a relatively independent storage
local area network, so as to achieve a maximum degree of data sharing and data
management, as well as seamless extension of the system. From the organization of
a data storage system, DAS, NAS, and SAN can all be divided into three parts: (a)
disk array: it is the foundation of a storage system and the fundamental guarantee
for data storage; (b) connection and network sub-systems, which provide connection
among one or more disc arrays and servers; (c) storage management software, which
handles data sharing, disaster recovery, and other storage management tasks of
multiple servers.
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