Author: Rachelle Trent, SAS Product Manager,
PMC-Sierra
SAS Provides Scalability
- Capacity: maximum 16K devices
- Expanders enable capacity scalability
- Bandwidth: in multiples of 3Gb/s
- Wide links provide bandwidth aggregation
- Increased storage capacity via cascaded JBODs
As enterprise storage requirements rapidly increase, expanding data throughput and providing scalable storage capacity is crucial. One of the benefits of Serial Attached SCSI (SAS) is overcoming the scalability limitations of parallel SCSI and significantly increasing the scalability to 16K devices. Scalability is provided by a device element called an expander, which interconnects hosts to storage through a network of multiple expander devices. In addition to scalability, SAS expanders enable fault-tolerant systems and facilitate the compatibility between SAS hosts and SATA disk drives.
The scalability of SAS was demonstrated at the recent SAS Solutions Open House event on May 9 in San Jose, as shown in Figure 1. A SAS server is connected to a SAS switch which, in turn, is connected to several JBODs. The switch uses a SAS expander inside to interconnect the SAS Server with the JBODs. Inside each JBOD resides an expander that provides fan-out to all of the HDDs and provides an extra connection for additional storage. This connection of JBODs in a series is called “cascading” and provides a simple method to greatly expand storage capacity.
