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iSCSI inspires low-cost storage networks
There's been a stream of iSCSI products since

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the ratification of the iSCSI protocol in early 2003. Managers can now choose viable storage products from multiple vendors. iSCSI brings block-level SAN technology to smaller shops.

iSCSI enables block-level data delivery over any IP network. With an iSCSI initiator on the server, the system can send block-level data over the IP network to a storage device. Because Microsoft provides an iSCSI initiator as part of Windows "you've got SAN enablement being given away with the operating system. You don't even have to buy any [additional] hardware," says David Dale, chairperson of the Storage Networking Industry Association's IP Storage Forum.

The poor performance iSCSI was once criticized for no longer presents a problem in an era of gigabit and multigigabit Ethernet networks and fast processors. Yes, IP adds overhead, but "IP networks today are plenty fast," Dale says, even without the help of TCP/IP offload engines. iSCSI performance problems are more likely to result from disk drive actuators unable to pull data off the spindles fast enough, he says.

With iSCSI, midsize shops and satellite offices of large companies can achieve the benefits of consolidated networked storage. "Fibre Channel was the first phase of consolidation for enterprise mission-critical applications. With iSCSI, we can have a second phase for Wintel servers, which will be used for file consolidation," says Michael Peterson, president, Strategic Research Corp.

Mesirow Financial, a Chicago-based diversified financial firm with 800 employees and 11 offices found itself with a large number of Windows servers and the problem of administering DAS for each. "A SAN was too expensive," recalls Jay Walusek, vice president of server administration at Mesirow. After Microsoft added iSCSI initiators, the company researched an iSCSI SAN, settling on an iSCSI appliance from EqualLogic with 14 SATA disk drives. The appliance "virtualizes the storage for us and provides data replication at no additional cost," he adds.

Mesirow's next step is to add a second iSCSI appliance in a suburban office and run a gigabit Ethernet connection between them. "That will allow us to replicate data off site," Walusek says. The company also wants more SATA arrays for disk-to-disk or disk-to-disk-to-tape backup. Making this all possible is iSCSI, asynchronous IP connectivity and SATA disk arrays. "We get a fully populated, redundant iSCSI SAN for about $40,000 to $50,000," he says.
By definition, the word "secondary" suggests some degree of inferiority, but in a storage area network (SAN), secondary storage can bring big savings and smoother operations. Toss out the derogatory inferences--lower cost disks with less than breathtaking performance are playing an increasingly important role in the storage architecture.

Lower cost, of course, can be relative. Although ATA and Serial ATA (SATA)--i.e., "cheap disks"--often come to mind when secondary storage is the topic, the term doesn't necessarily define a product category.

Depending on a company's business environment and the currently installed equipment, secondary storage may just as easily be an older network-attached storage (NAS) box or a SAN array, basically any storage device that performs at a lower level than what's required for critical applications. Of course, it's prudent to keep an eye on TCO; maintaining older, lower performing storage may actually cost more than simply replacing it.

For most companies, placing a second class of disk storage between their primary storage and their archival tape library is the first step toward a tiered storage environment. Pair second-tier storage with a second-tier network--iSCSI--and the vision of a storage network architecture that can meet most of the cost/performance scenarios in the enterprise begins to take shape (see "iSCSI inspires low-cost storage networks"). But to effectively deploy secondary storage requires an understanding of the nature of the data, the data's value, how often it's used and how frequently it's accessed.

Add to lower-cost the notion of migrating data from primary storage, and this new layer of disk extends the old idea of hierarchical storage management (HSM). Instead of HSM's nearline layer--usually easily retrievable tape or writable optical--secondary disk storage brings instant online access and the ability to control whether data can be rewritten or not.

Why tier?
There are two motivations for adding secondary storage to an environment: improving data protection and making more cost-effective use of installed storage systems. From an applications perspective, these two criteria break down further, addressing more pecific storage activities:

  • Creating a more effective disaster recovery plan that allows data to be copied and recovered faster
  • Dramatically improving the backup process to gain freedom from backup window constraints
  • Making better use of primary storage by moving less-frequently used or less-critical data from expensive arrays
  • Maintaining older information in an easily accessible form to satisfy business and regulatory requirements
The concept of migrating data isn't new. HSM has been used in the mainframe world for decades, but in open-systems environments, migrating data from one type of array to another has heightened the importance of secondary storage. By using online storage resources, secondary storage extends the HSM concept.

"The majority of people up until recently have always treated all their storage the same," says Nancy Hurley, a senior analyst at the Enterprise Strategy Group (ESG), a Milford, MA-based analyst firm. But by moving data from one class of disk to another based on business criteria, companies have taken a significant step toward an information lifecycle management (ILM) system. Most companies first consider a secondary storage scheme to improve their data protection, adds Hurley.

Jim Geis, director of storage solutions at Forsythe Technology, a Skokie, IL, consulting firm, says that for many organizations, secondary storage provides a way to create multivendor shops. Multiple vendors typically meant multiple tools to manage storage, but Geis says that the maturation of management tools has made mixing vendor products much easier. Regulatory compliance has also forced storage shops to consider secondary storage, according to Geis. He says that because some regulations require almost immediate access to and a quick recovery of data "tape is not really an option."

SATA/ATA spurs interest
Clearly, more than a few planets had to align to put secondary storage in the orbit of storage managers, but the emergence of low-cost disks may be the prime mover. ATA and SATA disks are clear-cut alternatives to higher performing, more reliable--but much more costly--Fibre Channel (FC) storage.

At last spring's Storage Networking World conference, International Data Corp. (IDC) predicted that by 2007, 22% of all enterprise drive purchases will be SATA, accounting for 41% of the total terabytes purchased that year. This indicates growing interest in SATA, which is expected to account for less than 10% of 2004 drive purchases. IDC's prediction underscores the attraction of SATA/ATA disk, which today offers higher capacity than FC disks for 30% to 50% less cost.

The reliability issue is knottier. Regardless of the performance level required, any corporate data that's retained has intrinsic value and must be protected. One reason SATA disk prices can be kept so low is that the drive manufacturers do less testing on them than on typical enterprise-class drives. Reliability uncertainties may be the greatest impediment to SATA's acceptance. Forsythe's Geis says his clients' attitude about SATA can best be summed up as, "SATA is still wait and see."

Large storage vendors, such as Hitachi Data Systems (HDS) and Sun Microsystems Inc., are taking steps to help improve the reliability of SATA disks, or at least to take some of the unpredictability out of their failure. HDS' recent announcement of its Serial ATA Intermix Option allows the mixing of SATA disks with FC disks in the same array. HDS is taking a number of steps to improve the reliability of its SATA disks, including doing a read verify of every byte written to disk and continuously monitoring the disk with head sweeps.

Chris Wood, a director of technical sales and marketing at Sun, says SATA reliability is a "very significant issue." Wood says that when a disk fails, it usually occurs during its first 30 days of use, and that failure rate is higher when the disk manufacturers perform a shorter burn-in cycle, as is often the case with SATA disks. So, Sun adds a longer burn-in cycle and provides monitoring tools for SATA disks in service. For the future, the company is also looking at installing extra hot spares in every array that can be turned on when needed.

Most SATA arrays will be RAID protected, which will mitigate many of the reliability concerns, providing ample insurance if a drive fails. A second drive failure while the first is rebuilding could be a problem, but vendors are already addressing this somewhat unlikely occurrence. Network Appliance Inc. introduced double parity RAID (RAID-DP) with version 6.5 of its Data Ontap operating system. RAID-DP adds a second diagonal parity stripe and another parity disk to a RAID set to further safeguard the disks.

Another approach to improve reliability involves adding dual-port capability to single-ported SATA drives to provide redundant data paths. This technique is used by Engenio Information Technologies Inc. (formerly LSI Logic) in its SATA storage systems. Hewlett-Packard Co. (HP) is taking a similar tack with Fibre-Attached Technology Adapted (FATA), which it developed with Seagate Technology. FATA provides a dual-port FC interface for SATA drives, which improves reliability and allows mixing low-cost and FC drives in a single HP EVA array. These enhancements may kick up the cost of SATA disk systems a bit, but they will still offer substantial cost savings over their FC counterparts.

This was first published in August 2004

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