Storage Topologies: An analysis of DAS,NAS ,SAN

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Previously we discussed about the concepts of Enterprise Storage and what the enterprise has to look for while implementing storage solutions. The technology shifts such as the impact of networking technologies and that of parallel processing along with some inherent bottle necks in the present storage architecture of DAS (Direct Attached Storage), resulted in mutually co-existent methods for connecting storage to computing platforms. We analyse some of the storage topologies of DAS (Direct Attached Storage), NAS (Network Attached Storage ) and SAN (Storage Area Network) and their inherent features.

Direct Attached Storage:

In this topology, most of the storage devices such as disk drives, disk arrays and RAID systems are directly attached to a client computer through various adapters with standardized software protocol (like SCSI, Fibre channel). This type of storage is alternatively called captive storage or Direct Attached Storage.



As said earlier there were some inherent disadvantage in this type of architecture. Explains EMC country manager T Srinivasan, "In DAS architecure, there were inherent bottlenecks such as lack of interoperability between different platforms, operating systems and devices. Direct Attach Storage (DAS) can only scale along with the server that it is attached to, whereas SANs allow flexibility to use and scale the increased information servers".

DAS is an appropriate choice for- very low end PC applications, very high-end high-performance mainframe applications and certain other computer intensive and high performance OLTP database applications.

DAS Topology (Source: Auspex systems white paper)

Network Attached Storage (NAS)

In contrast to DAS, network standards are strong standards that are driven by system considerations. They are used for accessing remote data that have been broadly implemented by virtually all UNIX and Windows NT system vendors. As a result, storage devices that serve data directly over a network are referred to as Network Attached Storage (NAS) and are far easier to connect and manage than DAS. NAS devices also support true file sharing between NFS (Network File System) and CIFS (Common Interest File System) computers, which together account for the vast majority of PCs sold. NAS evolved from the networking industry where there are strong standards for connectivity, data security and load balancing. NAS is a more mature technology and deployed in every other enterprises today.



NAS is the best choice for UNIX and Windows NT data sharing applications Consolidated file serving applications Technical and scientific applications Internet and Intranet applications e-Business and certain types of Decision Support (DSS) applications

Network Attached Storage (NAS) topology(Source: Auspex systems white paper)

Storage Attached Network

SAN evolved from the storage industry where standards are weak, therefore SAN implementations are not standardized. SAN is deployed in 1 of 20 enterprises. Because of its current lack of standards SAN is available only in proprietary configurations and the long-term inter-operability of these schemes is still not apparent. Although the SAN vision involves many benefits now available on NAS, there are certain synergies with existing enterprise operational and management tools that have led early adopters to experiment with test deployments.



Although the long-term SAN vision is for inter-operability among heterogeneous servers and storage products, it is advisable to implement early SAN applications in a homogeneous environment with one of the available proprietary solutions from EMC, HDS or Compaq. SAN is also appropriate for applications that do not require true data sharing, a feature not likely available until SAN standards evolve to the level of those available with NAS today. SAN is also appropriate for applications where the well known Fibre Channel (FC) and Fibre Channel Protocol for SCSI (FCP) security risks can be managed and where performance bottlenecks arising form Fibre Channel node and link congestion can be avoided.

The inherent advantage of SANs are that they also tremendous flexibility in deploying new applications.;The backup and restore mechanisms inherent in storage infrastructure cascade across existing and new applications. Finally, given the fact that storage requirements are likely to double every twelve months, manageability of the information explosion is best done through scaleable implementations of SAN, as part of the Enterprise storage networks.

SAN topology(Source: Auspex systems white paper)

Previously we discussed about the concepts of Enterprise Storage and what the enterprise has to look for while implementing storage solutions. The technology shifts such as the impact of networking technologies and that of parallel processing along with some inherent bottle necks in the present storage architecture of DAS (Direct Attached Storage), resulted in mutually co-existent methods for connecting storage to computing platforms. We analyse some of the storage topologies of DAS (Direct Attached Storage), NAS (Network Attached Storage ) and SAN (Storage Area Network) and their inherent features.

Direct Attached Storage:

In this topology, most of the storage devices such as disk drives, disk arrays and RAID systems are directly attached to a client computer through various adapters with standardized software protocol (like SCSI, Fibre channel). This type of storage is alternatively called captive storage or Direct Attached Storage.



As said earlier there were some inherent disadvantage in this type of architecture. Explains EMC country manager T Srinivasan, "In DAS architecure, there were inherent bottlenecks such as lack of interoperability between different platforms, operating systems and devices. Direct Attach Storage (DAS) can only scale along with the server that it is attached to, whereas SANs allow flexibility to use and scale the increased information servers".

DAS is an appropriate choice for- very low end PC applications, very high-end high-performance mainframe applications and certain other computer intensive and high performance OLTP database applications.

DAS Topology (Source: Auspex systems white paper)

Network Attached Storage (NAS)

In contrast to DAS, network standards are strong standards that are driven by system considerations. They are used for accessing remote data that have been broadly implemented by virtually all UNIX and Windows NT system vendors. As a result, storage devices that serve data directly over a network are referred to as Network Attached Storage (NAS) and are far easier to connect and manage than DAS. NAS devices also support true file sharing between NFS (Network File System) and CIFS (Common Interest File System) computers, which together account for the vast majority of PCs sold. NAS evolved from the networking industry where there are strong standards for connectivity, data security and load balancing. NAS is a more mature technology and deployed in every other enterprises today.



NAS is the best choice for UNIX and Windows NT data sharing applications Consolidated file serving applications Technical and scientific applications Internet and Intranet applications e-Business and certain types of Decision Support (DSS) applications

Network Attached Storage (NAS) topology(Source: Auspex systems white paper)

Storage Attached Network

SAN evolved from the storage industry where standards are weak, therefore SAN implementations are not standardized. SAN is deployed in 1 of 20 enterprises. Because of its current lack of standards SAN is available only in proprietary configurations and the long-term inter-operability of these schemes is still not apparent. Although the SAN vision involves many benefits now available on NAS, there are certain synergies with existing enterprise operational and management tools that have led early adopters to experiment with test deployments.



Although the long-term SAN vision is for inter-operability among heterogeneous servers and storage products, it is advisable to implement early SAN applications in a homogeneous environment with one of the available proprietary solutions from EMC, HDS or Compaq. SAN is also appropriate for applications that do not require true data sharing, a feature not likely available until SAN standards evolve to the level of those available with NAS today. SAN is also appropriate for applications where the well known Fibre Channel (FC) and Fibre Channel Protocol for SCSI (FCP) security risks can be managed and where performance bottlenecks arising form Fibre Channel node and link congestion can be avoided.

The inherent advantage of SANs are that they also tremendous flexibility in deploying new applications.;The backup and restore mechanisms inherent in storage infrastructure cascade across existing and new applications. Finally, given the fact that storage requirements are likely to double every twelve months, manageability of the information explosion is best done through scaleable implementations of SAN, as part of the Enterprise storage networks.

SAN topology(Source: Auspex systems white paper)