RAID controllers.

From the largest data center down to the small office/home office-computing environment, RAID is becoming ubiquitous. No longer is this technology reserved for the deep IT pockets of Fortune 500 corporations. At the same time, new architectures are allowing more modular approaches to data storage giving customers similar performance and functionality of monolithic data center storage.

Sub-Entry Level RAID

Serial ATA technology has accelerated the demand for low-cost yet high performance and highly redundant RAID solutions fur the lowest-end servers and workstation environments. RAID vendors are offering a variety of solutions from integrated RAID on Chip (ROC), host chipset-based and discrete host bus adapter-based software assisted solutions that most frequently offer RAID-0 and -1, and in some instances a combination of both (RAID-10 or 0+1).

More feature-rich offerings are finding their way into solutions where system builders are willing to sacrifice some overall system performance for expanded array manageability and functionality, but require some host CPU overhead for 10 processing.

Vendors that choose software-assisted RAID solutions typically require data redundancy with enhanced features such as bootable arrays and other fault-tolerance capabilities such as robust error recovery, error logging and SMART polling. These solutions also offer the flexibility of supporting multiple operating systems that offer users a common interface for array configuration and management.

Midrange RAID: The Sweet Spot

The largest segment of the RAID marketplace continues to be entry-level and midrange servers (and some workstations) with direct-attached storage (DAS) requiring high-performance hardware-based RAID with parity data generation (RAID-5) support. This market also requires robust array configuration and management utilities as well as powerful array and media diagnostics and other capabilities to ensure the highest levels of data integrity.

Currently dominated by discrete dual-channel RAID host bus adapters, high-density server form factors and higher RAID take rates are driving the increase of lower-cost single-channel adapters and integrated RAID on motherboard solutions. As the requirement for RAID on servers reaches attach rates of 80% or more and the cost of storage space continues to grow, the attractiveness of ROMB as a cost-effective RAID solution will continue to emerge.

In order to meet the demands of a market that is continually changing and evolving, RAID vendors that can offer the most modular and portable software solution with the most extensive and flexible media monitoring and error tracking capabilities will be able to meet the needs of this growing marketplace. User-friendly management utilities that are easy to use and can manage a diverse array of storage scenarios will dramatically impact market acceptance as well.

From DAS to Modular iSCSI

The desire for the flexibility and availability characteristics inherent in modular external storage are starting to drive an increasing number of these customers to investigate low-cost external storage. The trend has also opened doors to new, more cost-sensitive markets that were once excluded by the higher costs involved in external storage systems supporting RAID. This in turn has resulted in the industry driving new and emerging interface technologies to match the market need. The interface landscape is rapidly changing on both the target and host sides of the storage framework to resolve lingering storage I/O bottlenecks, signal integrity and other system-level issues.

The convergence of the two known technologies, IP and SCSI, has led the storage market to comfortably embrace iSCSI--a point-to-point technology where one end is the storage subsystem and the other is connected to the application host through the Ethernet switch. Until now, the lack of a simple, integrated and intelligent iSCSI-RAID target solution has delayed and created a gap in the deployment of IP SANs. Today, vendors are combining RAID technology with the price/performance advantage of iSCSI and Serial ATA to close that gap.

This approach enables storage integrators to deploy target subsystems with proven RAID functionality into the IP SAN market. Now, the low-end to midrange market can expect storage subsystem manufacturers to offer affordable, yet modular, solutions that meet the price/performance expectations of the DAS market model.

Storage Systems

Current economic conditions are clearly driving a trend in the industry towards bringing down the costs of all storage solutions. This has driven players typically providing midrange enterprise solutions to seek ways to place their enterprise-level storage system software stacks onto low-cost PCI host bus adapters like external RAID hardware architectures. The product category created by this type of product could be considered "entry enterprise."

The goal of this new type of marriage is to create very cost-effective storage with many of the same attributes of robust data center storage. These storage systems tend to have performance adequate to support 20-50 drives, depending on application workload, with maximum capacities approaching the maximum nodes a FC loop can support. Using 73GB or larger drives, storage system capacities of 2TBs make these systems a good fit for a growing number of business applications that at one time required companies to purchase more expensive systems to meet application capacity requirements.

Since these entry enterprise systems use the same code load as their big brothers do, they also provide many of the same features, such as LUN masking, hot spares and non-disruptive FW upgrades. Most also have limited forms of replication features such as remote mirroring, snapshot or mirrored volumes, making them a truly enterprise system but at a very reduced price.

Up from the entry enterprise market exists the core of the traditional modular midrange storage system market recently re-labeled mid-enterprise by some. Traditionally, these systems have been attached to open system Unix servers and systems running mission--critical business applications in, many times, very sophisticated corporate storage environments. Increasingly, these systems have also started to be used to service high-end Microsoft environments as corporations have traded-in their Unix storage systems in recent years. This market typically requires that storage systems provide high availability, high data integrity and storage platform resident data management tools.

Mid-enterprise platforms typically have many of the features you would expect in an enterprise platform. They tend to vary based on their larger caches, better processor performance, better cache performance, greater number of back-ends for capacity and throughput, and greater number of front-ends for performance and host connectivity. They may also come standard with some of the features that are optional on entry systems. This makes these platforms more appropriate for high-end servers or fur storage system consolidations supporting multiple servers.

As previously discussed, modular enterprise platforms have now stepped up to provide many of the monolithic enterprise value propositions. Monolithic architectures still seem to stand out in a couple of important areas such as larger cache capacities, support for OS/390 and the ability to provide a large number of concurrent data transfers out of their front-end host connections.

While modular enterprise systems have made many advances in recent years, their primary weakness is in using them for storage consolidation and very large-scale storage environments. This weakness comes from the fact that these systems tend to be deployed in a distributed fashion for these applications, thus creating logical barriers to data access between and across arrays.

Recently, the high-end storage segment of the storage business seems to have turned its attention towards addressing this limitation--not with the monolithic products of old, but by creating hybrid technologies. Their goal is to leverage the costs and capabilities that now exist in the form of modular storage products, while at the same time providing the single entity, ease of administration provided by the high-cost, buy-your-frame-all-at-once, monolithic architectures of today.

What Lies Ahead for Storage Systems?

Just like the rest of the storage market, enterprise storage systems are evolving at a quick pace. Today, most support Fibre Channel drives on their back ends. It is too early to tell the size of the impact SAS drives will have, but it is not too early to predict that some vendors will attempt to create systems using them. Whether future arrays use SAS or FC drives, expect many suppliers to improve diagnostics and increase performance by the use of switches and a mesh to connect their drives. For some enterprise applications SATA drives will be offered, bringing to market yet a third drive option for customers to consider. And lastly, expect that all enterprise suppliers will quickly move to supply faster host connections. Some will supply the newly defined 4Gbit FC connection while others will skip directly to 10Gbit; most suppliers will probably be forced to support both. With so many advances still left to be implemented in storage offerings, the storage landscape will be changing and shifting significantly in the years to come.

www.lsilogic.com

Jim Evans is product marketing manager and Dennis Hahn is product planning manager at LSI Logic Corporation (Milpitas, CA)