Storage Area Networks (SANs).
These more basic secondary storage devices are directly connected to a
host computer or server. For instance, disk drives for disk backups,
RAID arrays, and tape libraries for tape
backups are DAS systems, usually connected by standard protocols like small computer system interface (SCSI). The numerous variations of SCSI developed by vendors create numerous
component-driven storage standards. Data retrieval is at the block level.
DAS systems are used for local file sharing.
RAID is an acronym for Redundant Arrays of Inexpensive Disks, coined
in an era of Single Large Expensive Drives (SLED) to basically mean
"Don't put your eggs in one basket." (These days, with change and perhaps
inflation, it typically is known as a Redundant Array of Independent Disks.)
There are several types of RAID, but the concept is the same: an array
of disks composed of various sized stripes of usually redundant data.
This increases speed and fault tolerance.
NAS is composed of both hard disks and management software, and is
completely dedicated to serving files from a company network running a
Gigabit Ethernet. It is based on standard network protocols such as TCP/IP,
FC, and CIFS. NAS systems typically consist of RAID systems and software
for configuring and mapping file locations to a network-attached device.
Storage is shared across multiple servers.
A storage area network, or SAN, is a highly scalable, dedicated,
high-speed storage network of devices for transferring large blocks
of data securely among servers, networking components, and storage
devices. It is separate from the corporate local area network (LAN).
In a SAN infrastructure, storage devices such as NAS, DAS, RAID
arrays, or others are connected to servers using highly reliable
interconnect technology called Fibre Channel or,
in the case of IP SANs, Internet Protocol. Serial ATA and Serial Attached SCSI
interfaces are also making headway with SANs.
DAS, NAS, and SAN all offer benefits, but each is best suited for a
For more information on choosing the right solution for your
company, please read our
Storage First Steps.
Go to Bitpipe Research Guide: Storage.