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Issue of August 2004 

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Down the SAN memory lane

In some cases, especially when it's time to prove the ROI you might wonder why did you or would you invest in consolidated storage, like a SAN or NAS. Joe Hernick reminds us of why the centralized storage system is so crucial to any comtemporary business.

The best way to manage your data storage is to centralize it. Moving from a distributed model to a centralized one can increase application reliability, decrease staffing needs and enable "just in time" storage allocation.

Most important is centralized storage's zero downtime. The problems that plague distributed data storage are unlikely to occur in a centralized environment. Fewer overall storage devices, more robust management systems and centralized backup can translate into 99.999 percent uptime.

With DASD (direct-access storage device) arrays, redundant fabric switches, robust backup devices and storage-management software, your distributed-platform site can attain mainframe-level storage integrity and reliability. These technologies have been delivering in the big iron world for years-and you'll find storage vendors are more than happy to offer the goods for your Windows or Unix platforms.

Where your storage dollars go

Zero downtime is probably the most compelling reason to centralize storage, but there are less obvious cost benefits. Decreased storage reserves can generate substantial savings. All shops keep an available stockpile on each of their storage environments. A site may have 500 servers, with each one connected directly to a 50GB RAID. The usual modus operandi is to maintain an average 20% reserve in each environment to handle short-term growth. It's a smart strategy, but it means a lot of unused storage on each box.

Moving from distributed storage to a single environment greatly reduces the need for a surplus. Instead of a separate pool on each box, you'll have a smaller, centralized store for any of the connected environments. Administrators can then set standard threshold alarms for capacity limits and allocate storage from the centralized pool as needed.

Automation tools reduce the significant labor costs associated with storage-provisioning tasks, according to a Yankee Group report. What's more, centralized storage is easier to manage than distributed storage once it's up and running, thanks primarily to fewer moving parts. With fewer devices and more robust management tools and flexibility, your IT staff can concentrate on more pressing issues.

McKinsey & Co. says SAN and NAS solutions yield economies of scale that can reduce staffing costs by up to 80%. Shops with large-scale SANs manage storage four to eight times more efficiently than those using conventional methods. So if your site has four people managing the storage farm, it may take only one person to deliver the same level of support post-centralization.

At a minimum, a happily humming SAN or NAS implementation will free staff from the drudgery of storage management. No more never-ending tape swapping, RAID-drive replacement or dry eyes from reading capacity monitors. By consolidating your data-center storage, you move all your RAID stacks and tape loaders into one area. When it's time to swap a drive or load your DLT, everything is right at hand, rather than in a locked cabinet halfway across your production floor.

There are plenty of real-life success stories.

Recently, a capacity-management type told us his storage centralization tale. His company, a Fortune 500 financial services firm, was looking at a large server refresh (more than 1,400 boxes) in its primary data center.

The company's prior operating model had left it with old, out-of support DAT or DLT autoloaders on every creaky Wintel server in the shop. The firm's final design gave it a roughly three-to-one server consolidation, with all data storage moved to a Fiber Channel SAN with centralized backup. Instead of buying 400 autoloaders for the new boxes, the company built up its existing SAN (which until then served only the mainframes and a small subset of midrange environments) and improved its reliability and performance. The savings realized from not buying hundreds of new autoloaders paid for the lion's share of the company's new DASD. Other savings resulted from reduced physical-plant requirements.

Moving the SAN out to all the systems not only freed up floor and rack space, but also reduced power and HVAC demands. As a bonus, the smaller footprint meant the crowded data center didn't need to be expanded.

Rather than laying off people, you can temper staffing plans to reflect the efficiencies of centralized storage. The same number of folks you have managing 2TB in your direct-connect world may be able to manage 4, 8 or 13TB down the road as you grow in a centralized environment. Break down your staffs' duties to the task level to determine where they'll save time and you'll have the metrics you need to project future savings.

Recognizing that one person can manage only a fixed quantity of servers and direct-attached storage, calculate the threshold points at which you'll need additional staff to support growth. Your staffing-cost curve becomes a step model, with a big jump each time someone is hired; as you move into the future, staffing costs will likely increase faster than hardware costs.

Direct-attached storage makes sense in a small shop: If you're plotting 100% growth over five years, your dozen servers and 2 TB might still be manageable when they blossom into 24 servers and 4 TB. But if you're running 400 servers with the same projected growth, how many more folks will you need to stay on top of 800 servers and their routine maintenance, break-fix and upgrades? Growth is good for the company, but it can be rough on the operations staff.

That's where the benefits of centralized storage come in. All "care and feeding tasks" are greatly reduced, thanks in large part to a reduction in the number of moving pieces. Instead of monitoring RAID controllers in each server, you need only sit on top of your SAN console. Data purge and archive, disk maintenance and other routine activities can be managed as a whole rather than server by server.

Centralized storage can also enable more nimble responses to storage requests, improving user and management perceptions of your performance. In a direct-attached environment, each server and application requires solid capacity planning for future growth.

One way to mitigate these risks is to set triggers and alarms. You also can minimize them by influencing user behaviors and maintaining sufficient buffers of excess capacity on each server. A well-designed NAS or SAN will let operations staff dynamically allocate additional storage in response to any of these issues. Instead of scrambling to stay one step ahead of the storage ceiling on each of your DAS boxes, a centralized solution will let your staff work more fluidly with business and applications teams to manage spikes and surges.


Compared to direct-attached storage, network attached storage gives you a leg up in terms of management tools, integration, cost-effectiveness and reliability, NAS systems are packaged as easy-to-install "appliances."

Connecting to your LAN and using remote console management, these solutions are typically seen as a standard file share on the network. NAS enables a file system to be handled remotely (usually via CIFS or HTTP), with redirector software sending a file request over the network to the centralized storage device to serve up data. More robust solutions scale as requirements grow via modular construction, and they can provide NFS (Network File System) and SMB (Server Message Block) connections. Depending on your performance requirements and budget, you can outfit your NAS with dual NICs, Gigabit Ethernet and ATA/IDE, SCSI or Fiber Channel drives.

You can improve reliability by going in for multiple power supplies and redundant cooling fans. Backup solutions can be directly connected or network-based.


A storage area network is dedicated solely to data storage and retrieval. Its main components are storage devices and an independent network. The storage components include fast disk drives and large-scale tape backup devices, with storage-management software tying it all together. Network hardware may include switches (Fiber Channel in FC SANs, Ethernet in iSCSI) that let components talk to one another, as well as connectivity bits such as HBAs (host bus adapters), which connect external devices to the SAN.

Ideally, the switching fabric makes it possible for storage devices from multiple vendors to interconnect and function with multiple operating environments-letting, say, IBM AIX, MVS, Sun Solaris and Windows 2000-hosted applications access common physical storage environments. SANs rely on either Fiber Channel technology, which provides high bandwidth (2Gbps) linking storage components, switches and HBAs, or iSCSI technology based on standard IP topologies. SANs were initially proprietary Fiber Channel architectures; but iSCSI is the new kid on the block, generally offering a lower-cost, if somewhat slower (1Gbps) alternative. Either option can incorporate legacy SCSI devices. There may be some performance degradation with legacy drives, but the ability to maximize existing capital investments can strengthen the business case.

A solid design should rely on dual (redundant) switches with ISL (interswitch links) and dual HBAs to provide maximum uptime for connections between storage subsystems. There's a lot of dispute between proprietary versus open standards for SAN architectures and the FC SAN industry has yet to sort it out. Right now, CIM/OM (overlapping with Bluefin) and SMI-S are the leading FC standards.

The bottom line

SANs are expensive and not easy to implement. Few shops have any in-house FC experience, and few training centers or schools offer FC curricula. Thanks to basic economics, you can bet that any FC consulting you bring in-house will be dear. Because iSCSI relies on conventional IP, this type of SAN will be more familiar to your staff.

NAS provides an excellent, relatively inexpensive solution for smaller enterprises. FC SANs deliver performance for those who can justify the high cost of implementation. iSCSI SANs fall somewhere in between, leaning more toward the FC model than the NAS one in terms of cost and performance. If you need the reliability of a SAN, want to utilize your existing IP know-how and are satisfied with the Ethernet switching speeds, iSCSI may be the best solution for you-and may likely yield the best business case after you run the numbers.

The benefits of centralized storage management really come out as the size and demands of the enterprise grow. The bigger your shop, the more demanding your customers and clients, and the more convoluted your existing storage schemes. Therefore, the more you can benefit from centralized storage. The technology is cool, but money matters more. Emphasize revenue gains, increased service levels, happy customers and reduced expenses. After all, these are the benefits of storage centralization, regardless of which method your company chooses.

Courtsey: CMP Business Media

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