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Spotlight on midrange arrays

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EMC's CX700, packed with sophisticated replication and management software, is built to be the workhorse of the data center.
EMC Clariion CX700
The Clariion CX700 represents the top of EMC Corp.'s modular storage line. When pundits talk about modular storage encroaching on high-end enterprise storage, they're referring to products like the CX700 (starting price is $100,000), which is bundled with sophisticated replication and management software.

"The CX is the most successful product in this market segment," says Randy Kerns, senior partner, the Evaluator Group, Greenwood Village, CO. EMC packs the CX700 and smaller CX500 with a broad set of software, including the Navisphere Management Suite, SnapView, MirrorView, SAN Copy, PowerPath, VisualSAN and VisualSRM. "It has a comprehensive suite of data management software, extensive application and operating systems support, and good performance. It also supports FC and ATA drives within a single system," notes Tony Asaro, senior analyst, Enterprise Strategy Group (ESG), Milford, MA.

Kerns is impressed with the CX line's asynchronous and synchronous remote replication,

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particularly its support for consistency groups. This capability ensures write order is maintained when replicating data, a critical feature when replicating databases.

Currently, the CX700 offers both FC and ATA drives. Jay Krone, director of Clariion marketing, says the company is committed to following the ATA technology, which implies it will be moving to SATA. The company's design principle for Clariion dictates using only off-the-shelf components rather than custom-developed ASICs, which leaves the product a step behind the leading edge. The same design principle, however, also allows the company to drive down the price and ensure reliability.

Although EMC doesn't offer iSCSI for the CX700, it recently announced iSCSI for the lower end of the Clariion CX line (CX300 and CX500). Analysts have welcomed the announcement. "EMC supporting iSCSI is important because in many people's eyes, this legitimizes iSCSI," says Asaro.

iSCSI aside, Asaro complains that the company may be a little slow in moving to new technology. "The Clariion is a great product for the last generation of storage systems," he says. "ESG recommends that EMC add more advanced software, such as thin provisioning, snapshot copies and n-way scalability." Thin provisioning provides dynamic capacity allocation during write operations. N-way scalability requires the array to support more than two controllers. At this point, few modular arrays provide n-way scalability or thin provisioning, although that's coming, adds Kerns.

For small businesses, the PS100E is simple to set up and operate.
EqualLogic PS100E
When EqualLogic Inc. introduced its PeerStorage arrays, the so-called PS line was recognized as a fast, simple way to implement a SAN. Based on iSCSI, the company boasted that users needed no special skills and the box could be set up without training in 20 minutes.

The PS100E, with dual controllers and 3.5TB of SATA drive capacity, costs approximately $40,000. Although typically equipped with 7,200 rpm SATA drives, a firmware enhancement now allows the PS line to support 10,000 rpm drives.

In addition to the hardware, the PS100E includes an extensive set of browser-based management capabilities, including point-in-time copies, volume cloning, self-healing disk technology that identifies failing disks and activates spares residing in the cabinet, multipath I/O and security (CHAP support). Built-in load balancing automatically distributes the workload across all disks as new capacity is added, even splitting previously existing volumes across the new disks. As a result, the PS line can scale simply by plugging in more arrays. The PS100E's management console, however, is proprietary and doesn't support CIM, which poses some challenges if you want to manage the storage environment with a different management tool.

"EqualLogic is a young company, but it's starting to get traction," says Dianne McAdam, senior analyst and partner at Data Mobility Group LLC, Nashua, NH. The product's appeal to this point has been to the small- and medium-sized business (SMB) market, based on its low cost and easy installation.

However, it's the scalability of the PS line that has attracted attention of late. "EqualLogic storage systems have a network clustered architecture that allows customers to add nodes to scale. By adding nodes, customers get additional processors, bandwidth, cache memory and capacity in a near linear fashion," says Tony Asaro, senior analyst at Enterprise Strategy Group (ESG), Milford, MA.

In a 2004 study, ESG found that a single PS array can support 50,000 IOPS out of cache. A 25-array system produced 1.2 million IOPS out of cache. Theoretically, a 32-array PS system should achieve 1.6 million IOPS out of cache, ESG calculated.

PS array pricing is competitive for its class: "iSCSI inherently reduces cost and complexity since expensive Fibre Channel gear is no longer required," says Asaro.

With its remote replication capabilities, and the ability to allocate capacity in small 1GB increments, HP continues to improve the EVA.
Hewlett-Packard EVA
Hewlett-Packard (HP) Co.'s StorageWorks Enterprise Virtual Array (EVA) is in many ways a pioneering example of modular arrays. Originally introduced in 2001 by Compaq as VersaStor, the EVA is arguably still the only "virtual array" available from a major storage vendor. A virtual array, in HP parlance, goes beyond simply binding physical disks into a RAID group. Instead, the EVA presents all its capacity as a virtual pool of blocks from which users can carve up pools with different availability and performance requirements, while the EVA manages the underlying physical disk resources.

The two current EVA offerings are the EVA3000 and the EVA5000. The EVA3000 scales to 56 disk drives or a maximum of 16.8TB of raw capacity using 300GB FC disk drives. The EVA5000 supports up to 240 disk drives for a maximum of 70TB raw. EVA features include dynamic capacity expansion--which allows an administrator to allocate capacity in 1GB increments--virtual disk data load leveling as a non-disruptive background activity and distributed sparing of disk capacity.

Last year, HP added support for Fibre-Attached Technology Adapted (FATA) drives. The 250GB drives are based on low-cost desktop disks, but connect using FC and can plug into any existing EVA drive shelf without modification or bridging. Initially, about 10% of new EVA customers chose FATA disks; over time, HP expects FATA to account for about 25% of EVA drives.

Last month, HP announced a major enhancement to the EVA's controller-based replication software, HP StorageWorks Continuous Access EVA. Part of HP StorageWorks Business Continuance Software Solutions family, Continuous Access EVA now works with new Metrocluster and Continentalcluster software, which allows users to failover storage and servers across geographically dispersed locations.

The EVA line will be refreshed by midyear, according to Kyle Fitze, director of marketing for HP's online storage division, with a focus on scalability, performance, interconnect technology and additional disaster recovery capabilities, such as automatic failover across clusters of servers and storage. HP's long-term challenge will be defining what part EVA plays in its vision for grid-based storage. Certainly, the plan would allow using an existing EVA as part of the StorageWorks grid, Fitze says.

This was first published in March 2005

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