This article can also be found in the Premium Editorial Download "Storage magazine: Best storage products of the year 2002."
Download it now to read this article plus other related content.
I don't recommend the daisy-chain approach in general. Spend the money, buy more switches and design an architecture that will allow the availability, performance and flexibility necessary when SANs become larger and need to scale. For us that meant trunking ISLs when possible as well as building out core-edge topologies that scaled. This also let us take advantage of storage resources by merging fabrics when necessary, without having to schedule downtime. This approach also allowed us to build on our earlier investment in smaller switches - we introduce newer, faster, larger switches at the core and push the older, smaller ones to the edge or to development environments in some cases.
While it is possible to build out a core-edge topology using smaller switches, it's more cost-effective to use bladed directors with a large port count if high availability and increased flexibility are the goal. However, whether using smaller switches or large director switches to build your core-edge topology, the key is to pick an architecture that will scale for your environment.
While architecture is crucial, you can also avoid future costs by building out the right SAN infrastructure and how you connect servers to storage resources.
Start out small, and run fiber under the floor for a few hosts. But as you grow and have to move, add, or retire servers, switches, tape libraries and storage arrays, maintaining the fiber under the floor can be cost prohibitive. Troubleshooting a connection problem can be difficult with so many strands running on top of each other in a spaghetti fashion. Labels can become inaccurate or removed altogether from handling and moving the cables so many times.
If you don't have an infrastructure in place, you could end up with a lot of wasted fiber under the floor that could involve downtime to pull. Build the storage network like any other network and include patch panels with bundled fiber running between and distributed throughout the data center(s) in a design where the anticipated length from any server, storage array, switch and tape library can be calculated and preordered.
Understand the soft costs
One of the biggest soft costs when implementing and administrating a SAN are the people. This is probably because companies such as Intuit are telling vendors that such a tool is needed, a number of vendors are working on ways to easily administer the SAN from a centralized location and eliminate the manual bookkeeping tasks.
As our SAN grew from 20TB to 50TB to 200TB and over 900 switch ports - the old ways of managing were no longer practical. The spreadsheets we started with that detailed how the zones and disks were configured to the hosts wouldn't scale effectively. Again, this worked initially but keeping the documents updated always seemed to take a back seat to keeping the trains running.
Choose a SAN management tool early in your SAN deployment to cope with future growth. Good tools have widespread benefits in the area of interoperability, planning, scaling, and space reclamation (see "The right stuff").
If there's one thing I've learned from our whole experience, it's that basic technologies change rapidly. Absorbing them while running a real environment means you have to have good policies, procedures, design and management tools - so don't wait too long until you do that.
Now that we've arrived at a scalable architecture and infrastructure, we know what we need for management tools, and implementation is our biggest challenge. We're currently focusing on three main pain points. Implementing an enterprise resource management tool, better and more efficient ways for data archiving and remote data facility replication for achieving ensuring higher levels of data integrity and usability in the event of a disaster.
Change is still the order of the day. But I believe that with the current state of the art and the lessons that pioneers such as Intuit have learned, many companies can start at a reasonable level and grow into the many terabyte range while preserving most of their initial investment.
Online resources from SearchStorage.com: "The science of SANs," by M.C. Kinora.
This was first published in January 2003