Managing and scaling IP SAN

Computer Technology Review, Nov, 2004 by Peter Wang

Despite the slower economy, data continues to grow at a fast pace. Fueled by the data intensive new applications such as streaming content production and distribution, surveillance video, compliance archival, remote backup data centers for disaster recovery, etc., the demand for networked data storage and access is accelerating capacity-wise, while the total projected storage market remains essentially flat. The drive by IT organizations toward efficiency in capital equipment and human resource utilization is highlighted by the server and storage consolidations, which is pushing the conversion from direct attached storage (DAS) to network attached storage (NAS) and storage area networks (SAN). The DAS to NAS/SAN conversions, as well as the new data-intensive applications, are underscored by the requirements for inherently scalable and manageable distributed storage infrastructure.

Addressing Network Storage Needs with Native IP SAN

With the availability of the iSCSI (Internet SCSI) standard from the Internet and Engineering Task Force (IETF), a number of iSCSI products have been introduced into the market. The early applications have been the iSCSI-FC (Fibre Channel) gateways and switches, which address the server fan-in economic challenge of the FC SAN and the connectivity among FC SAN islands across the wide area network (WAN). The availability of the software iSCSI drivers across major server operating systems, including Windows, Linux, Solaris, HP-UX and the forthcoming drivers for AIX and Mac OS X, in conjunction with the iSCSI storage arrays offers the IT organization the potential to implement IP SANs to address many of their data storage needs.

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The performance and storage pooling benefits of the SAN, as demonstrated by the FC SANs, are broadly accepted. IP SAN offers similar benefits at much lower total cost of ownership (TCO) by leveraging the commodity Ethernet switches and the abundant IP network administration knowledge base. Many IT organizations that are planning or implementing PC server and storage consolidation projects are now considering or deploying IP SAN, both for the economic benefits and to avoid the need to acquire and manage a second and different network environment, i.e. FC SAN. The most notable applications are Web, e-mail, and CIFS/NFS file services.

Disk-to-disk backup, near-line archive, and remote disaster recovery sites are the other key applications where the native iSCSI storage arrays are being considered and applied. In these cases, IP SAN is used as auxilliary storage to the more expensive FC SAN. IP SAN's cost-performance offers a much better fit and value than even the FC SAN with the serial-ATA (S-ATA) disk arrays. The increasing number of iSCSI disk array offerings, known as "bricks," will accelerate this trend.

Learning From the Evolution of FC SAN

As iSCSI disk arrays and IP SANs proliferate, there are a few lessons to learn from the FC SAN evolution and recent trends.

As the FC disk array grew in size, the high-end, monolithic, FC storage subsystems (e.g., the Symmetrix DMX, the Hitachi Lightning, etc.) were endowed with switched internal fabric for increased performance, virtualization for simplified volume management, and advanced features such as snapshot and remote replication. The same trend also occurred among the mid-range modular FC SAN storage subsystems, albeit in a slightly different form. To address the challenges and overheads of managing zoning, LUN masking, and the large number of host-LUN mapping and routes on the application hosts, the out-of-band (or asymmetric) virtualization appliance and the in-band (or symmetric) SAN volume controllers were introduced. In essence, virtualization has moved beyond the hosts and into the fabric.

The other interesting development has been the introduction of NAS heads to front-end the FC SAN for file sharing. This movement leverages the dynamic scalability of FC SAN storage to address the capacity limitation of the conventional monolithic NAS design.

The complexity of FC SAN management aside, the common themes among these trends are:

* A key benefit of the SAN is its ability to scale, by extending the fabric and attaching more devices

* SAN management becomes unwieldy as the number of "components" within the SAN escalates

* Moving intelligence (i.e., storage resources virtualization and data movement) into the fabric to simplify host and data management

A Scalable, Highly Available, Managed IP SAN

The FC SAN development trends and benefits to the user IT organizations can be realized by a native IP SAN, and without the complexity of the FC SAN management. The native IP SAN is constructed by connecting the iSCSI disks, iSCSI JBODs (Just a Bunch of Disks), or the increasingly available iSCSI RAID arrays (known as "bricks") to one or more storage services controllers (also called SAN volume controllers or virtualization appliances by some vendors), which in turn are connected to the application hosts via iSCSI again.