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IP-SAN, the networked storage wave-of-the-future?

This article deals with a subject possessing definite lines of demarcation, strong favoritism and intense opinion: Networked Storage. Whether SAN, NAS or IP-SAN, no one networked storage technology is better than the other for every client and for all purposes, as each possesses its own unique attributes and advantages.

This article focuses on the newest networked storage technology, IP-SAN, which is gaining considerable momentum within organizations of all sizes. In many cases IP-SAN is the perfect fit as a total storage solution. In others, it is proving an excellent tool when used as an integral part of a more global, mixed-architecture infrastructure solution for improved backup/restore, disk staging and efficient/economical data replication.

Networked Storage Architecture--A Primer

Networked storage architecture has enabled organizations to effectively share, consolidate and manage data resources, more so than with DAS (Direct Attached Storage). The shift from server-centric to networked storage has been dependent upon technologies designed to transfer data to and from storage repositories as fast as, or faster than, direct attached technologies, while overcoming the limitations inherent in parallel SCSI, the main interconnect for DAS.

All data is stored on disks in block form (without file-system formatting), whether originating from applications as blocks (as in most database applications) or as files. Parallel SCSI transmits data to storage in block format with limited usefulness for networks because cabling is limited to 25 meters. In addition, it cannot connect more than 16 devices per network.

Fibre Channel is currently the dominant infrastructure for SANs. SAN technology places storage resources on a dedicated high-speed Fibre-Channel network. This protocol technology grew from the need to provide high-performance transfers of block data, as well as the need to overcome the connectivity and distance limitations associated with DAS. Common Fibre Channel installations connect devices up to a distance of about 10 kilometers. More costly solutions extend that distance to several hundred kilometers without imposing practical limits on the number of devices to which is can be attached.

Unlike SANs, NAS transfers data in file format over an IP network. NAS devices use the Server Message Block (SMB) protocol to transmit database block data. However, this is less efficient than using the Fibre-Channel SCSI-based protocol.

Is IP-SAN the Next Paradigm Shift?

IP-SAN represents a new generation of networked storage. It combines the best attributes of Fibre-Channel SANs (functionality and scalability) with the best attributes of NAS (ease-of-deployment and ease-of-use) providing virtually all the capabilities of Fibre-Channel SAN and NAS devices combined (file and block-level storage) but at significantly lower cost. IP-SANs scale to Petabytes in size and can be managed as one realm, locally or remotely. Like NAS, IP-SAN takes advantage of existing GB Ethernet network infrastructures, although for security and performance purposes it is usually implemented as a separate network off the main network infrastructure.

Like their SAN and NAS counterparts, IP-SAN offers useful and cost-saving capabilities, such as: dynamic storage allocation (expanding storage on the fly); RAID striping and mirroring (for increased performance and reliability); snapshots (for fast backups and restores, as well as near-production development); Replication (block-level--only the changes are replicated locally and to the remote site).

Key IP-SAN Components

1. iSCSI Client/Host

The iSCSI client or host (also known as the iSCSI initiator) is a system, such as a server, that attaches to an IP network and initiates requests and receives responses from an iSCSI target. Each iSCSI host is identified by a unique iSCSI qualified name (IQN), analogous to a Fibre-Channel world-wide name (WWN). To transport block (SCSI) commands over the IP network, an iSCSI driver must be installed on the iSCSI host (iSCSI drivers are included with Microsoft's iSCSI initiator). A Gigabit Ethernet adapter (transmitting 1,000 Megabits per second--Mbps) is recommended for connection to the iSCSI target. Like the standard 10/100 adapters, most Gigabit adapters use Category 5 or Category 6E cabling. Each port on the adapter is identified by a unique IP address.

2. iSCSI Target

An iSCSI target is any device that receives iSCSI commands. The device can be an end node, such as a storage device, or it can be an intermediate device, such as a bridge between IP and Fibre-Channel devices. Each iSCSI target is identified by a unique IQN and each port on the storage array controller (or on a bridge) is identified by one or more IP addresses.

Business Cases for IP-SANs

Reduced Buy-In and Scalability Costs

Well-designed IP-SAN solutions preclude clients from buying more infrastructure than is required. By separating controllers (the brains) from the disk shelves (the data repositories), end-users can design solutions that fit their current requirements without having to invest prematurely. As additional performance is required, controllers are added. These controllers scale linearly in performance and load-balance across the entire realm. (Should only storage capacity be required, additional drive shelves are added without the need to purchase additional controllers or chassis and without the need to bring the system down.


Internet SCSI (iSCSI), an industry standard was developed to enable transmission of SCSI block-commands over existing IP networks by using the TCP/IP protocol. iSCSI offers organizations the possibility of delivering both messaging traffic and block-based storage over existing Internet Protocol (IP) networks, without having to install a separate Fibre-Channel network.

iSCSI Advantages

Long-distance connectivity

Fibre-Channel SANs installed in organizations with offices distributed over wide areas could possess unlinked "SAN islands" that cannot be bridged past 10km. Although there are new ways to extend Fibre-Channel connectivity up to several hundred kilometers, these can prove complex and costly. iSCSI over WAN (Wide Area Network) provides cost-effective long-distance connectivity that can be used as a bridge to existing Fibre Channel SANs or between native iSCSI SANs. This utilizes in-place MANs (Metro Area Network) and WANs.

Lower costs

Unlike Fibre-Channel solutions that require a completely new network infrastructure, solutions such as clustering are simpler with iSCSI than with Fibre-Channel. iSCSI SAN solutions capitalize on preexisting LAN infrastructure and utilize the IP expertise already available within most organizations.

Simple use implementation and management.

iSCSI solutions require little more than the use of the Microsoft iSCSI initiator on a host server, a target iSCSI storage device and a Gigabit Ethernet switch to deliver block level storage over IP. Managing iSCSI devices for storage configuration, provisioning and backup can be easily handled by the system administrator similar to how such operations are handled for DAS.

An Analysis of the Costs--DAS (Direct Attached Storage) vs. iSCSI SAN vs. Fibre-Channel SAN

There are two types of costs associated with purchasing new storage. The first, hard/direct costs bears directly on the IT budget and includes capital spending, labor, outsourcing, professional services, support contracts and training. The second, soft costs, are less tangible and are often hidden. They include, loss of productivity or lost business revenue when a system goes offline for upgrades, repairs or to accommodate a large backup window. Both must be considered in order to accurately calculate the total cost of ownership (TCO). Based on deploying a 2 Terabyte SAN with backup using industry average list prices, iSCSI SANs can be less than half the cost of Fibre Channel technology with ongoing management cost savings. iSCSI also provides up to a 60 percent savings in storage administration costs compared to equivalent capacity DAS.


In the end, IT/financial decision makers must decide which solution(s) meets their exact requirements for performance, reliability, scalability and cost. Sometimes, the best solution utilizes multiple vendors' technologies, configured in a complementary fashion in order to solve several separate problems. The advice this author offers to clients who inquire about which networked storage technology is best for them is that they do their homework to learn the details of what each technology offers and then apply the technology that best fits their budget and unique current and future storage growth needs. The last thing anyone wants to have to do is to forklift out a solution they already invested heavily in just because their organization's data requirements continued to grow and what they had implemented could not keep up with the growth.

Ed Ginty is executive vice president of VLSystems (Irvine, CA).
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Article Details
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Title Annotation:Storage Networking
Author:Ginty, Ed
Publication:Computer Technology Review
Date:Jun 1, 2005
Previous Article:Scaling NAS with adaptive resource switches.
Next Article:Improving data availability with RAID 6.

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