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The evolution of midrange storage can make it confusing when deciding whether you need midrange or high-end systems, particularly if you just focus on specs. For example, several HDS 9500 V midrange systems with 4GB/s throughput could be placed in the data center to handle the I/O workload of 16 discrete applications, or a single high-end EMC DMX800 could handle the same workload. There's little difference in performance throughput, but the high-end system has at least two advantages--and you pay for this.
A quick look at the relative cost for 1TB of storage illustrates how much is being paid for the high-end advanced features and availability. For 1TB of midtier storage, the average cost across the vendors discussed here is approximately $50,000, while the entry point for high-end storage is a little less than $200,000. For this additional money, you gain added availability and functionality.
For example, at the midtier, you can still perform replication within the subsystem. But at the midtier level, you'll experience degraded performance and potential unavailability of applications. High-end storage subsystems with shared applications don't have these problems.
One disadvantage is resources consumed by each of the 16 applications ebb and flow as applications change and evolve. When one of these applications isn't running a cache-friendly access pattern, other applications use the latent resources.
Another difference is performance has more to do with sustained performance. For example, when ShadowImage software is running on a Sun high-end StorEdge 9980V, there's no noticeable decrease in performance on the subsystem. As a general rule of thumb, a high-end storage subsystem has from six to eight times the performance of a midtier solution on a terabyte-for-terabyte basis.
Another common misconception is that you can buy midtier storage and use host-based software products to deliver the functionality in a high-end array. Application program interfaces (APIs) for the midtier storage platforms aren't as feature-rich as those for high-end systems, thus storage managers aren't able to manage a lower-end solution as well as the high with the storage resource management platforms available today. There's been progress made in the common information model (CIM) standard, but more time is needed.
While there may be financial benefits to an n-tier environment, management and ease of deployment outweigh this consideration for most users.
Even at Inovant, manageability is a significant challenge in the service tier environment. "Our ideal solution would be some type of enterprise-level switched network-attached storage," says Cancilla, which he termed SNAS. This allows Inovant the ease of NAS management and the performance of a switched Fibre topology.
Both high-end and midrange storage are moving targets and continue to evolve. Some of what is expected on future products will change the debate about tiered storage.
Vendors and end users agree that the following is high up on their must-do and wish lists:
- Manageability: increasing the number of gigabytes managed per person.
- Visualization: the ability to have a single view of the SAN and associated components
- File sharing: virtualization at the file level and user view
- Service: providing storage as a service
Manageability continues to expand in breadth and depth through various software offerings and some management features are being built directly into the storage subsystems. The same management functions of high-end systems can be duplicated at the midtier, but at the cost of performance and availability. When determining the performance requirements of a storage system, take into consideration the subsystem operating at peak workload with advanced functions all running.
SAN visualization from a common set of tools is also emerging from both hardware and software vendors. In addition to visualizing the storage network from a hardware view, it's also important to increase usability of the end-user storage experience. This is becoming more important, since the amount of information a user is accessing daily is increasing. Hiding the complexity of the underlying information infrastructure will continue to simplify storage operations. One implementation of the virtualization concept is the development of a common file system that allows easier file duplication and sharing across mixed high-end and midtier environments independent of the attached host systems.
Storage as a service is a business trend that continues to formalize as storage becomes more of a commodity and business units push back on complex storage acquisition models. Both the midtier and high-end continue to evolve on fast and distinct paths in the storage community. Look for these tiers to coexist for quite some time with added manageability, visualization, virtualization and service utilization models.
This was first published in April 2003