Information Technology Reference
In-Depth Information
Interface Technologies
Before storage policies can be developed, the architect must identify exist-
ing interface technologies being used for data storage. Rather than differ-
entiating different types of data storage (such as optical versus magnetic),
the interface format each storage device uses affects which devices may be
physically aggregated and the rate of data transfer possible for each. These
interface solutions may be configured for parallel or serial data transfer,
making use of local or network-capable transfer protocols.
Parallel ATA ( PATA)
Modern parallel ATA (PATA) storage devices evolved from earlier
modified frequency modulation (MFM) and run length limited (RLL)
interfaces and include technologies such as the common integrated devel-
opment environment (IDE) interface. PATA devices are almost always
found in client computer systems rather than in servers, which employ
serial attached storage devices for higher transfer rates and resource aggre-
gation. PATA devices may be connected directly to a controller channel,
or they may be configured to share connectivity, with two or four devices
per channel in some cases. Although PATA devices require no path termi-
nator, they may be configured for dedicated master/slave relationships to
set device preference and boot order. These devices employ parallel data
paths, requiring wide cables that are unsuited to long distances and that
can increase thermal control issues in a data center environment.
Serial Attached Storage (SAS)
Data center server systems often employ serial attached storage solutions
such as small computer system interface (SCSI) and serial ATA (SATA).
These technologies allow for higher signal throughput and greater access
speed. The SCSI interface has multiple versions that are not directly com-
patible, as they vary in signal and voltage standards. Care must be taken
when planning SCSI storage consolidation to ensure that all devices in a
stack follow the same standard.
SCSI devices can be connected in series, typically with up to seven
devices per channel, and require a terminator to identify the end of the
signal path. Because serial signals can be transmitted over long distances,
