HP D2200sb Serial Attached SCSI technology, 3rd edition - Page 3

SAS technology, SAS devices - problems

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SAS technology SAS uses a point-to-point architecture that transfers data to and from SCSI storage devices by using serial communication (one bit at a time). The SAS architecture solves the parallel SCSI problems of bus contention, clock skew, and signal degradation at higher signaling rates. SAS devices use a differential signaling method to achieve reliable, high-speed serial communication. SAS inherits its command set from parallel SCSI and its frame formats and full-duplex communication from Fibre Channel. It uses the SATA interface for compatibility and investment protection. SAS offers an ideal solution for mission-critical enterprise storage applications because the SAS architecture features a proven SCSI command set, advanced command queuing, and advanced verification/error correction. SAS devices There are three types of SAS devices: initiators, targets, and expanders. Initiator devices include a host bus adaptor (HBA) or controller. The initiator attaches to one or more targets forming a SAS domain. Target devices can be SAS disk drives, SATA disk drives, or SAS tape drives. Expanders, low-cost, high-speed switches, let you increase the number of targets attached to an initiator to create a larger SAS domain (Figure 1). Vendors assign each SAS device a unique worldwide name (WWN) to identify it in a domain. Figure 1. Example of SAS and SATA devices in a single domain 3

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SAS technology
SAS uses a point-to-point architecture that transfers data to and from SCSI storage devices by using
serial communication (one bit at a time). The SAS architecture solves the parallel SCSI problems of
bus contention, clock skew, and signal degradation at higher signaling rates. SAS devices use a
differential signaling method to achieve reliable, high-speed serial communication. SAS inherits its
command set from parallel SCSI and its frame formats and full-duplex communication from Fibre
Channel. It uses the SATA interface for compatibility and investment protection.
SAS offers an ideal solution for mission-critical enterprise storage applications because the SAS
architecture features a proven SCSI command set, advanced command queuing, and advanced
verification/error correction.
SAS devices
There are three types of SAS devices: initiators, targets, and expanders. Initiator devices include a
host bus adaptor (HBA) or controller. The initiator attaches to one or more targets forming a SAS
domain. Target devices can be SAS disk drives, SATA disk drives, or SAS tape drives. Expanders,
low-cost, high-speed switches, let you increase the number of targets attached to an initiator to create
a larger SAS domain (Figure 1).
Vendors assign each SAS device a unique worldwide name (WWN) to identify it in a domain.
Figure 1.
Example of SAS and SATA devices in a single domain
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