Logical DesignWe feel that it is better for an enterprise to develop a storage architecture that all projects comply with, rather than letting every project develop its own strategy. With a well-thought-out plan for storage, teams working on new projects can spend time on designing and building applications without bothering with planning how to store data. Furthermore, the more you centralize your storage, the more you can simplify management and decrease complexity. One of the buzzwords these days is consolidation. Everything should be consolidated: databases, servers, applications, and so on. This is not a bad idea if you look behind the hype. Take storage, for example: Many companies have little control over where all data is located, since a lot of smaller databases are distributed around their networks. If you would have a strategy or a policy that dictates all data be located at the same place, you could utilize your storage space better, as you will see later in this chapter in the section "Centralized Model." SANs and NASs are great for accomplishing this. To illustrate this, we will now show you some examples of how you can develop your logical design for storage purposes.Distributed ModelIn a distributed model solution, such as the one shown in Figure 8-2, all servers have their own data stored on a DAS. An example that fits this model is a SQL Server that has its data files and log files on local RAID syst
Figure 8-2. A distributed storage design Although there are several benefits, such as flexibility, to this design, the disadvantages can outnumber these benefits. If you deploy this kind of solution, all projects need to have expertise in data storage applied during the design phase. The same storage decisions have to be made again and again, and this process is costly. Because data will be scattered in data islands all over the network, manageability will suffer. As you saw earlier, this situation can also lead to underutilization of the total storage capacity in the enterprise. This will inevitably lead to greater TCO than is necessary, making it an expensive solution in the end. Although this might seem like a cost-effective path to follow for a single project, the total cost for your company will be greater as time goes by.Centralized ModelThe opposite of a distributed solution is a completely centralized one, where all data is located on the SAN (see Figure 8-3). In this model, the operating system and application files are the only things placed on local hard disks. By using a powerful SAN, you can supply a solution that can fulfill the business requirements of an enterprise. Figure 8-3. A centralized storage design
The advantages of this solution are numerous. Since you keep all data in a central place you can also manage it easier. This lowers the TCO and makes it less expensive in the long run. You must be aware that the startup costs are high when implementing this design, however, but over time it is worth it. This is why it is important for an enterprise to have a clear view of how data should be stored from the start. If no guidelines exist, many projects will continue to invent their own solution every time. In the end, this will be more expensive than if a clear policy exists, even if the chosen policy might have a high initial implementation cost. Another benefit is that you can provide high security for the enterprise data, since you have it all in one place. This security does not come without manual labor, however, but is easier to set up with a centralized solution. A disadvantage with this solution, besides initial costs, is that you cannot distribute your data store to separate geographic locations. So if you are unlucky, you can lose a lot of data if the geographic placement of the SAN is destroyed. Without a doubt, this is sure to change in the near future; in the meantime you do have opportunities available to back up data to a separate geographic location, so you can overcome this problem.