Most IT managers know about the explosion in storage requirements that's been driven by e-commerce and other applications, and most have heard vendors extolling the virtues of storage-area networks (SAN) as a way of consolidating and better managing storage resources. But what's not so clear is the balance between costs and benefits.
Everyone offers the basic components - high-speed Fibre Channel hubs or switches that provide the high-speed 1G byte/sec. SAN backbone to which vendors attach disk arrays, tape libraries, optical disks and other resources. Servers access the SAN either through Ethernet bridges or by direct connection using a Fibre Channel host adapter.
Around this infrastructure, vendors add value by wrapping their own performance-tuning and management tools and by adding features ranging from the ability to dynamically reallocate storage among servers to fault-tolerance schemes. Each function you choose, however, adds to the total cost.
SANs are expensive, and prices vary widely. So what do you get for your money? What features do you really need? And what can you really afford? The three companies profiled below each had different storage requirements. And each chose a different vendor, spending from less than $200,000 to more than $1 million. Here's what they got in return.
Mission-Critical
WorldStor Inc. in Fairfax, Va., is a storage service provider, offering storage as a utility to companies that have elected to outsource their storage operations.
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Says Steve Bishop, the company's chief technology officer, "We stepped back and looked at exactly what we were trying to provide: an enterprise-class storage utility service that customers could bet their data on."
Bishop eliminated some vendors almost immediately. "The reason that we did not look too closely at some [vendors], including Compaq [and] Xiotech . . . is that we knew these companies were not far enough along in their development cycle to provide us with an architecture that was as stable and as well-tested as one from one of the big players," he says.
Bishop ultimately chose four EMC Corp. Symmetrix SANs, for two reasons: EMC's proven architecture and its extensive portfolio of management software. "Supplying raw capacity is the easy part [of our business]; it's managing the availability and the performance of the data that resides on that storage that poses the challenge. And those challenges are the very things that EMC develops its software to address," Bishop says.
He has worked with the SANs for a year and says they're "rock solid. We haven't had any issues." The four SANs hold between 5 and 10 terabytes (TB) of data each and use EMC's Symmetrix 8730 and 8430 storage array controllers, its Celerra File Server to make SAN volumes appear to remote clients as network-attached storage and its Connectrix Fibre Channel switches.
WorldStor makes extensive use of EMC's Control Center management software, plus Symmetrix Remote Data Facility for storage mirroring, TimeFinder for replication, Volume Logix for storage virtualization and Symmetrix Data Recovery software.
WorldStor's Symmetrix SAN didn't come cheap - Bishop says that the multimillion-dollar price tag that his company paid for its four EMC SANs is high, but he adds that WorldStor has saved thousands of dollars in software development costs because it was able to purchase software tools from Hopkinton, Mass.-based EMC instead of developing them in-house.
"So, in the long run, our total cost to offer the service to our customers, we don't believe, is any more expensive than some of the [storage service providers] in this space that are attempting to use more commodity-based products," Bishop says.
The Middle Road
When senior managers at Hannaford Bros. Co., a 112-store grocery chain based in Scarborough, Maine, first asked Doug Roberts, manager of network services, to look into a new SAN in 1998, they asked him to come up with a design that would tie into heterogeneous environments, including Unix, Windows NT and OS/390.
EMC was the only company that offered this capability, but it was unwilling to take systems responsibility for all SAN components. So Roberts focused on building a homogeneous system to support his seven Compaq ProLiant 8500 Windows NT servers, which provide e-mail, file and Web services. The applications weren't as mission-critical as the core business systems, but high availability was a requirement, particularly for file sharing and messaging, Roberts says.
He evaluated offerings from EMC and Compaq Computer Corp. But he chose Compaq's StorageWorks last December because not only would it provide all of the equipment, from the switches to servers and the disk arrays, but it would also support it.
"That's the big difference between the way EMC works and the way Compaq works," Roberts says. "EMC would point to Bus Logic or Brocade or Compaq and say, 'Those guys have the problem.' "
But EMC, whose Symmetrix SAN continues to run in Hannaford's mainframe environment, "is getting better," he says.
At the time, Compaq was also cheaper. "[EMC's] Connectrix switch . . . compared to the cost per connection in the Compaq system, was tremendously expensive," Roberts says.
Hannaford's StorageWorks SAN, deployed in April, consists of 2.6TB of storage, three StorageWorks RA8000 disk arrays, two eight-port Fibre Channel switches, a 16-port Fibre Channel switch and two RAID controllers. Roberts says the total price of the SAN, including the disk storage array, switches, host bus adapters and software (but not including the servers or installation), was approximately $250,000.
Roberts says the SAN improves the performance of his Notes servers dramatically. "We use RAID 5 in StorageWorks, and that's a six-channel connection to the disk. So it's very, very fast, and that really helps our Lotus Notes environment," he says. Similarly, the SAN delivers excellent file-serving performance because it provides access to a large amount of disk space.
For higher availability, Roberts uses SecurePath, Compaq's multipathing utility that reroutes disk data to an alternate path when it detects a failure on the host bus adapter, cable or controller and provides dynamic load-balancing to improve I/O efficiency. "If any component fails, the SecurePath software switches the route to a different SAN path without a glitch," he says. Roberts says he can easily change paths manually with a drag-and-drop procedure.
Roberts concedes that "Compaq's variety of systems they can connect to is immature. Compaq doesn't have the wide range of offerings that EMC does." That wasn't a factor for the project, but it's one reason an EMC SAN still runs on Hannaford's mainframes, Roberts says.
Roberts saved money by doing the setup in-house, but it wasn't easy. "The installation really requires a typical propeller-head," Roberts says. "But once the SAN is installed, running and documented, it works very well, and the tools do exactly what Compaq says they will do."
The Value Approach
David Hill, a network administrator at Andersen Corp., a manufacturer of
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| David Hill, Network administrator, Andersen Corp. |
Hill looked seriously at EMC, Santa Clara, Calif.-based Hitachi Data Systems Corp. and Hewlett-Packard Co. before choosing Eden Prairie, Minn.-based Xiotech Corp.'s Magnitude SAN. Andersen's technical committee reviewed proposals from all the vendors and cut the field down to finalists EMC and Xiotech before making its final choice.
The committee's criteria included interoperability, scalability, ease of use, the ability to operate in a heterogeneous environment (Unix and Windows NT) and price. It chose Xiotech because, for Andersen's needs, it stacked up well against the competition in all of those categories and cost less, Hill says. The total price tag came to less than $200,000.
Andersen uses two Xiotech SANs - one for development and a second for production.
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So far, Hill says he is impressed with the Magnitude SANs. "Availability comes down to more than just hardware redundancy," he says. "There are lower-cost solutions that adequately provide the hardware platform. Xiotech does that very well." Hill says the storage management software has been easy to use, and setup also went smoothly thanks to the plug-and-play nature of the product.
Final Decision
Choosing the best SAN for a company's needs and budget can be daunting, but some choices are clear. For high availability in mission-critical data centers, established SAN vendors such as EMC and Hitachi offer a mature architecture, sophisticated management and support capabilities, and an established track record (although companies like Compaq and Xiotech also offer high-end configurations and are closing that gap).
For less-critical needs, offerings from Compaq, Xiotech and others may offer what you need for less. But users suggest comparison shopping, since EMC and other high-end vendors also offer lower-end configurations and all vendors tend to discount substantially below initial sticker prices. A seemingly expensive SAN may actually end up being the more economical choice.
As it turns out, you can't buy a SAN on a shoestring budget. But with some smart planning, you can get the most cost-effective SAN for your company's needs - and perhaps save hundreds of thousands of dollars in the process.
SAN Features Shopping List
In addition to the basic hardware, SANs include a mix of features that can add considerably to overall cost. The key is to determine which features you need up front. Here's a quick rundown of common features - from the basic to high-end functions - and why you might need them.
Zoning
This basic function allows the grouping of SAN ports (and associated devices) by function or location so that many servers can share the same storage devices. While devices may be included in more than one zone, only devices in the same zone can "see" one another.
LUN masking
This basic feature keeps one server from overwriting a volume used by another server. Assigning logical unit numbers (LUN) is a way for a RAID storage system to present a hard-disk drive to a server. A basic SAN function, LUN masking makes specific LUNs (and hence devices) visible only to specified servers within the same zone.
LUN mapping
This is the ability to take one LUN and map it as different LUNs to multiple servers. It allows the SAN to work with some finicky server host bus adapters (HBA) that expect LUN numbers to appear in a specific order. This is less of a problem with newer HBAs.
Dynamic storage allocation
This allows available physical SAN storage resources to be reallocated among servers as needed.
Storage virtualization
This is the ability to carve up SAN storage from the physical drive pool into virtual drive volumes that can be shared to heterogeneous server environments. This level of abstraction makes volume management easier.
Nondisruptive backups
Software that manages SAN backup and restoration processes with minimal disruption to SAN performance. Tools are available from both SAN vendors and third-party suppliers.
Snapshot copy
To avoid performance hits from backups, users often create off-line copies of their data. But copying all blocks in a disk volume takes time. A snapshot copy takes a picture of the target volume's current state, creating a table of tracks, sectors and volumes that can be used to start backups sooner so they can be completed earlier - an important consideration when backup times are long.
Remote data mirroring
This enables the creation of remote mirrored data sets for rapid disaster recovery.
Remote data replication
Also called remote copy; it creates off-line mirror images of active production volumes that can be used to run data integrity checks and other tasks in parallel and without affecting response time performance of live data.
Multipathing
A fault-tolerance feature that reroutes data to an alternate path when an HBA, cable or controller fails. It may also provide dynamic load-balancing by rerouting data in the SAN to improve efficiency.
Serverless backups
This feature allows backups to take place across the SAN without server involvement. The device or software uses the Network Data Management Protocol to respond to a server agent's backup request to move data directly between SAN-attached disk arrays and SAN-attached tape storage. This feature requires special software from a tape backup vendor such as Pathlight Technology Inc. in Ithaca, N.Y. The relatively new, high-end feature can be expensive to implement.
Application fail-over
This feature supports clustered servers that have access to one another's data volumes but don't have to be running the same applications. When Server A fails, Server B accesses Server A's volume, launches the failed server's applications, accesses the data and takes over the function. This approach results in some downtime because the application must launch on Server B and users may need to reconnect.
Clustered application support
This is the ability of an application operating in a server cluster to pool multiple server resources together. When one server fails, the other keeps the application running against the same data volume. For users, the fail-over is seamless. Some SAN vendors offer features that enable this process to work more smoothly.
Clark is a freelance writer in Haverhill, Mass.