Storage Management Strategies for the CIO
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TCP/IP accelerators - NAS takes a performance hit when it's attached to the Internet and uses the TCP/IP. Basically, these network protocols ensure the delivery of data by segmenting and reassembling the transmitted packets, as well as checking the packets for errors. The software to accomplish these tasks is implemented on the requesting server and in the NAS controller. These transmission and error checking tasks eat up many processor cycles and degrade performance. Recently, vendors have started to move some of the TCP and IP processing software out of the server and onto a host bus adapter - called a NIC, for Ethernet networking, which lets the processor do other useful work and provided a significant performance boost. Of course, the old NICs and drivers must be replaced, but the performance gains are well worth the effort and expense.
DAFS - DAFS is a new technology (see "
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How DAFS will change networked storage," April 2002) that speeds up access to storage over a network by using the virtual interface (VI) architecture rather than TCP/IP. It uses the remote direct memory access (RDMA) implementation of VI to transfer data directly between a NAS device and the application memory space or a layer of software to handle the VI if the application isn't VI-aware. By setting up a direct VI, the overhead of the operating system and the TCP and IP protocols is eliminated. To utilize DAFS, the NAS appliance must support DAFS and have a VI-capable NIC or HBA card installed along with the appropriate driver.
NAS with metadata serving - When NAS is combined with a metadata server, it provides the simplicity of file-level access with the performance of a SAN. Here's how it works: A metadata server is accessed with normal remote file system semantics such as NFS or CIFS, but that access is used to identify the location of the data on the SAN-attached storage and that information is returned to redirector software on the requesting server. The redirector software does the high-speed block I/O over the SAN. This is also termed a SAN-NAS convergence and from the user standpoint, it becomes transparent as to whether the data is being accessed with block I/O or file I/O. The administration would be different because the redirector software must be installed and the metadata server administered as a special purpose server, usually in a clustered environment or with an internal failover capability. Examples of this product include IBM's TotalStorage 300G with SANergy enabled, EMC's Celerra HighRoad or ADIC's CentraVision.
LDAP (lightweight directory access protocol) - To improve security, some vendors are implementing the LDAP, which provides authentication for access to files on a NAS appliance. In addition, some vendors are tying the security controls for CIFS access into the Active Directory. This technology is in its early stages for NAS usage.
This was first published in July 2002
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