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Determining Organizational and Application Requirements
Determining your organization's storage requirements not only involves considering your company's business needs, but also any requirements related to your line of business applications. For example, a client application might need to access data on file servers by using a single UNC path, but your storage plan calls for providing fault tolerance by storing the data on two servers. The requirements of this client application could be met by implementing DFS. The first step in planning for storage, consequently, involves determining both the needs of your organization and the needs of your applications. Collectively, they will define your storage requirements. This process is shown in Figure 1.2.
Figure 1.2: Determining Organizational and Application Requirements
Determining Organizational Requirements
Organizational storage requirements go beyond having sufficient capacity for the data stored on each server and workstation. You must also satisfy redundancy and replication requirements. For example, to provide fault tolerance, you might decide to replicate data between two different file servers at two sites. In this case, you will need to ensure that there are sufficient storage resources at each site to store the replicated data.To determine your organizational requirements, it will be helpful to answer the following questions:What are your current priorities? You should focus on prioritizing which systems to address in what order. For example, mission-critical servers are more important than individual workstations. Prioritizing systems will help to define where you should begin when defining storage requirements, and is also important when budget concerns limit the amount of storage that you can immediately upgrade. When prioritizing, focus on maximizing return on investment and distributing the benefit of improvements to the largest possible number of individuals in your organization.What is the expected growth of data? Do not plan only for your current volume of data. Your plan should also include estimates of the size and expected growth rate of your organization's data.What are your budget constraints? Budget is always a limiting factor. Understanding your budget constraints reduces wasted design efforts and helps focus on improvements that can actually be delivered. You might consider a solution that technically addresses all of your needs, but you will need to find a compromise or an alternative if the necessary funds are not available.Can you consolidate storage? Consolidating storage reduces the cost of managing storage on multiple servers and increases the efficiency of storage allocation and backup tasks. However, consolidation also introduces risk, because more users depend on fewer servers; so an outage affects more users than in a more distributed installation. If you plan to consolidate storage, you should also investigate ways to increase storage availability.Will training be needed? It might be necessary for your administrators to get additional training. For example, administrators might be comfortable with planning simple clusters, but they should not attempt state-of-the-art Fibre Channel solutions without specific training. Make plans to build necessary training into your project and budget if you plan to implement storage solutions with a high degree of complexity, or with complex management interfaces.Will your storage needs change? Your storage needs are probably growing. It is easier to manage a flat growth rate than an explosive one, but in either case it is best to build flexibility into your storage plan at the outset. Implementing flexible Windows storage features now lets you adapt your plan later with little or no disruption to users. For example, DFS allows you to add servers transparently to your environment, and SAN-based storage arrays and network-attached storage appliances let you achieve higher storage utilization than direct-attached storage. Look for any upcoming projects or other business changes that might require additional storage.
How many copies of data are maintained? You need to plan adequate storage not only for primary copies of data, but also for any additional copies of the data that you need. Be sure to plan for the appropriate amount of backup media, and for sufficient online disk storage for shadow copies and replication.What are your performance requirements? Your choice of storage solutions is normally influenced by performance considerations. For example, your local area network (LAN) and wide area network (WAN) network components will likely need to be considered when planning for replication or data recovery between two systems in the same site, or between two or more systems in remote sites. Other considerations regarding performance include the type of server disks used, such as Enhanced Integrated Drive Electronics (EIDE) or Small Computer System Interface (SCSI), storage interfaces, and the speed of backup storage devices, such as tape drives.What are your backup scheduling requirements? You might have a backup window that must be met for nightly backups, or you might be able to run backups over their own network during the day. In addition to impacting the network, even backups made to direct-attached storage devices consume CPU cycles. Your backup plan should ensure that servers are available for clients and applications when they are needed most, and that backup activity does not impact network traffic during peak usage periods.How important is ease of backup and recovery? You might have the resources to manually back up your data nightly, and, in case of a system disaster, you might be able to bring in additional staff on an overtime basis to recover the information. Alternatively, you might require an automated approach that relies on high-end enterprise level backup software. Your plan for backup and recovery of data must balance your need for automation against the increased costs of various automated solutions.How long can data recovery take? Some critical systems must be continuously available. For example, an online banking enterprise might require that its system experience zero downtime. Other organizations might be able to tolerate a one-hour window of downtime. Your plan needs to take into account your organization's specific tolerance for downtime during data recovery.Will you use legacy equipment? Budget considerations sometimes dictate that you not replace existing equipment as you build your new storage environment. This is especially true for expensive storage libraries. The presence of older servers, disk arrays, cabling, and other equipment might save your organization money, but it might also dictate compromises in your storage plan. Also, if your plan calls for keeping existing technology, you might need to budget for any additional hardware needed to allow you to use the technology in your new storage environment.
Determining Application Requirements
When determining storage requirements, start at the application and operating system level, noting the storage and disk requirements for each system. For example, you might decide that your Microsoft Exchange Server requires 500 gigabytes (GB) of total storage, but you also need fault-tolerance. To configure a 500 GB RAID 0+1 disk array to provide fault-tolerance, you would need 1 terabyte (TB) of physical disk storage. You would also need to allocate drives for the Exchange transaction log files.Taking this approach server-by-server and application-by-application, you can determine the number of physical disks that you require, as well as the amount of total storage you need. When you estimate your total storage requirements, do not forget to include backup requirements. For example, you might plan to back up your Exchange server to a magnetic storage array for very fast backup and recovery performance, and then copy the backup data to tape for offsite storage. To keep a single full backup onsite would require that you double your storage estimate for the Exchange server. You will also need to estimate the growth rate of each database so that your storage meets both your immediate and future needs for a period of time as defined by your organization.When considering storage requirements for the operating system, you should note which servers require disk mirroring to protect their boot and system volumes, and note the number of required disks along with the amount of required storage for each.Estimating application storage requirements can be difficult without in-depth knowledge of all the applications that run in an organization. If your organization has designated specialists for your applications, consult with them to arrive at a proper estimate. The documentation for each application can also serve as an excellent source for compiling storage planning information
