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Serial SAN The Bright future of Serials
S.R. Prasana Kumhar
Monday, May 1, 2006
Serial Technology is here to stay! The staying power of this technology is amply demonstrated by the success of SATA drives and their deployment becoming ubiquitous with implementations ranging from desktops or servers to storage subsystems. Today organizations are deploying mission critical storage subsystems powered by SATA drives in their data centers to ensure performance and availability.

As most of us are aware Serial Attached SCSI (SAS) is a new enterprise disk interface. It was developed as a replacement to parallel SCSI to improve storage system performance, scalability, and availability while maintaining compatibility with the SCSI command set commonly used in today’s enterprise operating systems and applications.

Current Trends:
As far as the markets are concerned SAS technology is yet to gain its momentum as compared to that of the SATA, one could attribute this solely to the availability of commercial SAS based products from major storage vendors. Keeping in mind the popularity of SATA at the cost of ATA and SCSI technologies one could safely bet on the future successes of Serial Technologies be it ATA or SCSI. Both of them offer huge potential in a market that is conservative and tech savvy at the same time when it comes to implementing IT infrastructure.

In terms of connectivity technologies, the acceptance of SCSI based deployments of SAN for block level storage resource and management indicates a significant possibility for solutions based on Serial technology for deploying cost effective and user friendly SANs, in environments that ride on the SAS switches popularly know as Expanders.

Serial Technology at its best
With the advent of newer technologies both for processing data as well as those that enhance computing capabilities, a virtual ecosystem is being built that has given way for relentless explosion of data as well as persistent need for more and more space to store the same.

Each of the technology innovation has invariably led to more data. With businesses becoming more and more dependent on IT for its survival and growth, data has been the key asset that has to be stored efficiently and retrieved or used as effectively. This in turn has lead to formulating long term storage strategies that must take into account simplicity, cost effectiveness, scalability and performance as essential components.

One of the technologies that have been designed to address these components is SAS which was specifically intended to maximize the ease with which drives can be added to boost both capacity and throughput.

SAS Switches: Does it hold promise?
As most of us know SAS offers many benefits for enterprise IT infrastructures- thanks to its design and operation speeds. SAS, a point-to-point protocol, is a high performance, scalable, flexible and economical solution for deploying storage systems. SAS is a replacement for parallel SCSI, maximizing the ease with which data storage capacity and throughput is created. Its target application is direct attached storage (DAS) systems where one server is connected to multiple disks. One outcome of technology innovation is the SAS switches popularly known as SAS expanders, this holds a lot of promise to enhance the organization’s ability to deploy cost effective storage area network solutions.

Riding on the capability of design of SAS technology that provides a powerful switching capability the expanders act as switches to end devices, enabling quick aggregation of many drives in a single SAS domain (up to 16,384 devices). These switches are fully capable of connecting multiple hosts to multiple targets. This has lead to SAS switches beginning to attract interest as a medium for connecting large groups of targets in small storage area networks (SANs), in cluster or in blade server environments, allowing these servers to share resources across their targets.

SAS Zoning: Towards cost effective access control:
In larger environments, it is very important to provide for more management and control services. Furthermore the data traffic needs to be segregated for efficiency and performance issues. Because of the shared storage resource, server resources need to be controlled by putting limitations on which resources each server can control preventing unauthorized access. This is because not all servers need to access all data. The data access and retrieval is specific to the requirement of the application and the server and hence access control is a must, this will ensure efficiency in data movement and management as well as security. Access controls, such as those provided for by the SAS zoning specification; prevent unauthorized access, malicious attacks or corruption of data by operator error on the server. Access controls ensure that if a server is compromised; only data that is accessible by the compromised server is at risk of being lost and not the entire network.

SAS Switches with the access control functionality are used to control access to data since it is difficult to know if a host is authorized or not. This ensures that the hosts do not intervene or change their behavior. This further ensures that legacy SAS and SATA devices, which do not understand zoning, can operate within the SAS domain.

How does it benefit organizations?
Let us see what this means to the ever shrinking IT budget for organizations. Just imagine by latter part of 2006, servers available with SAS interfaces, or even low cost SAS interfaces available replacing the current U320 interfaces providing 3.0 Gbps throughput pipelines for your data from storage to the computing environments. The external SAS Interfaces are connected to a SAS switch that is capable of providing zoning; voila we have a SAS SAN that provides for cost effective SAS-SAN.

In terms of expansion the switches allows for keeping in view the point-to-point architecture of SAS design allows for a single SAS domain to contain up to 16,384 devices (128 maximum SAS devices per edge expander x 128 maximum edge expanders per fan-out expander) without performance degradation. And multiple SCSI domains can easily be interconnected to achieve remarkable levels of data availability. The best part is that the SAS switches accept both SAS drives as well as SATA as end devices.

Flexibility for IT Managers:
Since SAS controllers support both, dual-port, high-performance Serial Attached SCSI drives and high-capacity, lower-cost Serial ATA drives. The IT managers have the flexibility to purchase servers and storage systems that can be configured with either Serial ATA or Serial Attached SCSI disk drives or both, enabling the use of high-performance and low-cost disks in the same storage system.

This flexibility enables IT managers to use the same system for both, mission critical and business critical applications. This versatility reduces data center complexity by standardizing on one storage system for all applications. It also provides investment protection by letting IT managers redeploy storage systems to meet new requirements simply by reconfiguring existing systems with the drives best suited to meet a new application’s requirements.

SAS Switches/Expanders offer a lot of promise as the basic building block of cost effective Storage Area Networks for SMB segment in the near future as well as those upcoming companies that look for a value for money implementation when it comes to their IT infrastructure. With the advantages of the performance as well as cost of deployment well entrenched behind it, thanks to the 3 Gbps throughputs and promise of 6 Gbps and downward compatibility with SATA II devices, gives the SAS based switches one of the best possible chances to change the playing field in the storage infrastructure market place. A lot remains to be seen of how effective will the vendors be in a position to take advantage of the technology benefits that SAS has to offer.

S R Prasana Kumhar, is a member of SNIA India Technical Committee and Head -Products at XSERVE India Pvt Ltd., Bangalore, India.
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