Note that the table assumes all drives are operating at their maximum throughput simultaneously, and this does not always occur. It is also important to note that IOPs is often more critical than throughput in many applications today, depending on the circumstances. For these reasons, each configuration is normally able to support many more disks than indicated.
TRP: So how can SAS third generation improve performance for businesses?
TP: Being able to move at 12Gb/s means that measurements of over one million IOPS can be achieved. 12Gb/s SAS is an evolutionary change and a big step forward for the market. For the first time IT managers will be able to exploit the full potential of PCIe 3.0. This in turn will benefit businesses that rely on mission-critical data in a variety of environments, including transactional databases, data mining, video streaming and editing.
TRP: What are the issues in migrating to SAS third generation?
TP: The primary issue in the migration to third generation SAS is a familiar one: investment protection. Most organisations have made a significant investment in SAS disks, and want to preserve that investment when migrating to 12Gb/s SAS technology. The problem is: The third generation SAS standard maintains backwards compatibility by throttling down to the slowest SAS data rate in the system.
In small-scale point-to-point configurations, this is not always an issue because the migration would require upgrading both an Initiator and its Target. But in most organisations, such point-to-point configurations are rare.
The system-level "slowest data rate" performance limitation, therefore, means that in organisations without point-to-point configurations would not be able achieve the 12Gb/s performance boost until all disks support this new standard.
TRP: How can this issue be overcome?
TP: Fortunately there is a way to overcome this limitation, and that requires understanding a little about how SAS expanders function. A SAS expander makes it possible for a single (or multiple) Initiator(s) to communicate with multiple Targets concurrently. Expanders help make SAS remarkably scalable, and because each is capable of supporting multiple disks, expanders also makes it possible to aggregate the throughput of those disks.