SAN Buyers Guide: Part II Page 2


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Determine SAN Costs

The proposed SAN infrastructure has to have completed a logical design that will capture the design parameters and the list of components for the baseline costs in order to develop the proper payback models for the business case. This can be accomplished with a variety of services that can provide rough order magnitude (ROM) designs and costs based on information gathered from workshops or an onsite assessment. A preliminary list of SAN components (h/w, s/w, middleware, cabling, integration labor, etc.) can be summarized and priced, once the design is roughed-out and blueprints are available.

A useful comparative review of design and operational needs is provided by applying ROI models on more than one topology. Some topology design options can be very similar in price, but yield different total cost of ownership (TCO) cost streams or ROI payback terms. A balanced financial approach to the analysis and cost/benefit determination is created by having two or three topology options (network attached storage (NAS), point-to-point (PtP), FC switch or director, etc.). Since storage growth is assumed to continue regardless of the attachment architecture (small computer system interface (SCSI), FC, SAN, Enterprise Systems Connection (ESCON), etc.), some (but not all) of the SAN ROI analysis is completed without considering the detailed cost of storage. Thus, the cost of additional or replacement storage may need to be separated from any new SAN infrastructure costs when selecting and implementing a payback model/option. In other words, most ROI cases are prepared from the perspective of justifying the new SAN infrastructure, not necessarily the attached storage.

The future price of SAN infrastructure can be normalized to NPV cost or the average year costs, if the enterprise needs to migrate to SAN via PtP and small fabric installations (i.e., Fibre Channel Arbitrated Loop (FC-AL) or small switch). Future year, incremental growth will need to factor price erosion of future SAN components. It is often best to show total costs per usable SAN port as a comparison in the phased implementation, if an incremental approach to SAN is planned. Otherwise, for each SAN development phase, a separate ROI calculation would be needed.

Now, let's very briefly look at a few of the business planning cases that enterprises can choose from (who are currently working in a DAS environment), when performing a SAN ROI exercise to determine whether they should consider a move to their first SAN. Not all cases are equal in value and applicability to the target environment. Some cases are more specific to very large or mature enterprise infrastructures. Others are best suited for small sites, any kind of service provider (XSP), decentralized sites, etc. Those considering a move to their first SAN should be familiar with the following options in order to choose those that best apply to the target environment.

SAN ROI Case Selections

In order to build a business plan/justification, most enterprise environments choose between six and nine ROI business planning cases. Depending on the payback methods needed in the analysis, each case has specific characteristics that may vary, such as:
  • Achieving Service Level Agreement (SLA) targets.
  • Growth attainment.
  • Immediate cost reduction.
  • Long-term TCO reduction.
  • Operational efficiencies.

Next, let's look at these cases. In the interest of the length, only the most popular or widely used of the cases will be discussed in detail in this article.

Disk Utilization Increase

Improved storage asset utilization is inherently provided by pooled storage. As shown below, DAS storage can vary by platform:
  • Windows NT--20 to 40 percent average disk utilization.
  • UNIX--30 to 40 percent average disk utilization.
  • S/390--60 to 70 percent average utilization.

Disk Procurement Deference

In procurement, a pooled storage architecture provides better asset utilization and better efficiencies. However, future storage needs will emerge, regardless of how well the first consolidation effort goes. With larger, aggregated storage purchases possible, the future price of any disk bought will be cheaper per GB than storage bought today. Deferring as much capacity need fulfillment to the future as possible, will have a positive impact on near-term cash flow, since storage will be cheaper in the future.

Improvement Of Terabytes (TB)-Per-Administrator

Pooled storage increases the total capacity of data management that can be assigned to a DBA or storage administrator. Implementation of central, pooled, or SAN strategies, can reduce the staff growth requirements in comparison to staff needed to support server-attached distributed storage.

Data Center Rack/Floor Space Reduction

Server and disk consolidation represents real savings in data center floor space and environmental costs to the enterprise. Less space and power is needed to service data storage needs through aggressive consolidation and pooling of resources. These costs are true hard-dollar savings, and can start providing payback almost immediately. Since many enterprises are running out of space, the cost avoidance of building a new data center can be factored into the SAN infrastructure investment.

Tape Library Procurement Deference

Fewer tape devices will be needed to back up the enterprise data if the total disk capacity is smaller and the efficiencies of pooled storage work for the enterprise. For local backups of application data, OS, etc., some local drives that already exist can be used. However, to move off-line data from the central storage pool, larger enterprise tape libraries will be used. Many enterprise have multiple tape stackers, local digital linear tape (DLT), and 8mm drives attached to servers. Many of these can be replaced in favor of a better central library system. General estimates put a 15-to-25 percent tape unit savings through consolidation to larger silos. Depending on the decentralized state of the servers and the quantity of wasted tape space, efficiencies of 50-to-100 percent have also been observed. Since better tape utilization will be evident with pooled resources, fewer tapes will be needed. You can also calculate the effect of less time, handling, and the moving of tapes to off-site locations.

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