SMB migration to IP SANs.

According to leading industry analysts, the high-tech industry is finally crawling back to life post-Y2K, the 9/11 disaster and the dot-com bust. IDC predicts worldwide spending in information technology (IT) is expected to grow 5% to $916 billion in 2004. Recent government data indicates worldwide spending on information technology in the U.S. in 2003 is estimated to be $427 billion. Mid-size businesses (100-1000 employees) in the U.S. spend eight times more on IT than big corporations. Microsoft claims there are 8 million small businesses (100 or less employees) in the U.S., of which 19% have PCs attached to servers. Small to mid-size businesses (SMBs) represent 45% of all tech spending. Although direct-attached storage (DAS) continues to dominate, the total number of SMBs in the U.S. with networked storage (SAN/NAS) is expected to grow to 6.8 million by 2006. Government regulatory compliance with SEC Rule 17a-4, HIPAA, 21CFR Part 11, Sarbanes-Oxley, and the Patriot Act compliance are also driving SMB IT spending. The good news is that for the first time in years IT spending is on an upswing and SMBs will play a major role in making strategic (proactive) vs. tactical (reactive) network storage purchase decisions in 2004 and beyond. This article will provide guidance to SMB IT managers on how to implement a cost-effective IP SAN, describe the differences between NIC, TOE, iSCSI HBAs (initiators), and iSCSI storage (targets).

Building an IP SAN

SMB IT managers are expected to do more with less by prioritizing spending in key areas such as data protection, network security, storage capacity and management. Networked storage provides much needed relief, although it may be cost-prohibitive for many SMBs to install and manage a Fibre Channel SAN ($1,000/port). The solution is to build a storage network that can leverage an existing IP-based Ethernet infrastructure and allow the movement of block data between storage resources and computers. Enter the IP SAN. Internet protocol storage area networks (IP SANs) are based on the iSCSI protocol ratified in February 2003 by the Internet Engineering Task Force (IETF). iSCSI is a standard method of encapsulating SCSI commands into TCP/IP packets and transporting them over the ubiquitous Ethernet. Since IT personnel are already familiar with Ethernet technology, the total cost of ownership (TCO) for networked storage is dramatically reduced. IP-based storage can be shared among users and configured using existing network and storage management tools. In addition, iSCSI protocol over Ethernet enables network attached storage (NAS) devices to move block data.

SMB applications that can benefit from an IP SAN include e-mail, database (e.g., SQL, Oracle), streaming media, and remote backup. IT managers should note applications written for directattached storage (SCSI, ATA) may not tolerate the non-deterministic nature of Ethernet (network latency, packets arriving out of order). For example, Microsoft Exchange e-mail is not tailored for NAS (file I/O) over Ethernet. iSCSI can emulate SCSI direct-attached storage (block I/O). The option is to segment the IP SAN from the LAN, or create a virtual LAN (VLAN) in order to reduce congestion. IP SANs can also be blended with FC SANs using available IP-FC bridges and routers.

Figure 1 illustrates a three-tier small to mid-size enterprise (SME) architecture where legacy application servers (and clients) with DAS co-exist with database servers attached via Fibre Channel (SAN). However, SMBs may not be able to afford a FC SAN. An IP SAN can be created by segmenting the LAN for IP storage traffic and attaching Web or application servers with an optional network attached storage (NAS) device.

iSCSI Host Adapters (Initiator)

iSCSI combines storage and network characteristics. Host applications make write requests via iSCSI initiators to storage devices that are iSCSI targets, and targets respond to read requests. Host applications think they are communicating with a direct-attached SCSI device. SCSI command descriptor blocks (CDBs) are packed into a protocol data unit (PDU) by the iSCSI driver and are then passed onto the transmission control protocol (TCP) stack. The internet protocol (IP) provides the routing address of the destination device and the data-link layer sends the packet over the physical network (Ethernet) to the target iSCSI storage device.

[FIGURE 1 OMITTED]

iSCSI host bus adapters (HBAs) provide servers with a gateway to the IP SAN. iSCSI HBAs can provide Gigabit Ethernet network interface card (NIC), TCP/IP offload (TOE), and iSCSI protocol offloading. IT managers should note that not all HBA vendors are alike. However, HBA vendors vary on the portion of the TCP/IP and iSCSI protocols offloaded from the host CPU vs. how much protocol is actually hardware accelerated. Based on the 7-layer Open Systems Interconnect (OSI) model, a standard NIC only provides Ethernet (layer 2) and physical (layer 1) offload. TCP/IP offload engines (TOE) offload transport (layer 4), and network (layer 3). Only iSCSI HBAs that provide full protocol processing and host CPU offload (OSI layers 1-5) should be considered for building IP SANs.

Figure 2 illustrates the difference between a standard NIC, TOE, and an iSCSI HBA that provides full host CPU offload.

As a general rule, it takes 1GHz of host CPU to move TCP/IP traffic at Gigabit speeds. It is not unusual for host CPU utilization to exceed 80% using a standard Ethernet NIC due to TCP/IP processing overhead. The result is very few CPU cycles are left on the server to run mission-critical applications like email, database, or backup. The solution is to replace that aging 10/100 base-T NIC with an iSCSI HBA and immediately begin to reap the benefits of IP SANs. IP SANs enable SMB IT managers to run "enterprise strength" storage applications on existing Ethernet infrastructure at a fraction of the cost of FC SANs. IP SAN device discovery is provided by the Internet storage name services (iSNS), a protocol ratified by the IETF based on proven IP network and FC storage services. Finally, an iSCSI management application program interface (API) is in development by the Storage Networking Industry Association (SNIA) IP Storage Forum that will make iSCSI devices work seamlessly with existing network and storage management applications.

[FIGURE 2 OMITTED]

iSCSI Storage (Targets)

iSCSI storage devices (targets) receive and act on iSCSI commands from an iSCSI HBA (initiator). iSCSI storage devices such as disk and tape are now available from traditional NAS/SAN storage vendors as well as a number of start-ups. In iSCSI target mode the software stack shown in Figure 2 is simply reversed (OSI layers 1-5 are processed). The SCSI CDBs are then presented to an on-board SCSI controller (or another HBA) attached to physical SCSI drives. iSCSI storage controllers can provide Gigabit Ethernet NIC, TOE, and iSCSI protocol offloading. IT managers should note that not all iSCSI storage vendors are alike. iSCSI storage vendors vary on the portion of the TCP/IP and iSCSI protocol offload that is hardware accelerated, storage capacity (GB), and the number of Ethernet ports (aggregate performance). Only iSCSI storage controllers that provide full protocol processing (OSI layers 1-5) should be considered for building IP SANs.

A low-cost alternative to a dedicated iSCSI storage device is to convert a 2U server into an iSCSI storage appliance. Simply plug in an iSCSI HBA (target mode) and fully populate it with disks (SCSI, ATA) or attach just a bunch of disks (JBOD) or redundant array of inexpensive disks (RAID) subsystems through an external SCSI/FC port. Combined with storage virtualization software, storage appliances enable SMBs to consolidate legacy storage, dynamically allocate capacity, volume management, snapshot, remote data backup and mirroring for high availability and reduced total cost of ownership (TCO).

Features to look for in an iSCSI HBA include PCI bus support (PCI-X preferred), the ability to support host (iSCSI initiator) and storage (iSCSI target) modes, GbE NIC (dualport preferred), full TCP/IP offload (TOE), full iSCSI offload, compliance with industry standards (IEEE, IETF, SNIA), plus support for Microsoft Windows and Linux. To address these requirements, Xiran's DirectPath Accelerators (DPA) for IP Storage, powered by the company's patented DirectPath Engine (DPE), provide a flexible architecture featuring scalable performance, programmability, and industry compatibility to meet the needs of IP SANs. Xiran's DirectPath Accelerators fully offload all TCP/IP and iSCSI protocol processing to provide high performance, reliable and secure access to networked storage without burdening the host CPU.

In summary, SMBs in the U.S. represent 45% of all tech spending, which is estimated to be $427 billion in 2003. IP SANs enable SMB IT managers to run enterprise-strength networked storage for applications like email, database and backup over existing Ethernet infrastructure at a fraction of the cost of a Fibre Channel SAN. iSCSI leverages industry-standard IP network and SCSI protocols and services supported by Microsoft Windows and Linux. IP SANs based on the iSCSI protocol provide small to mid-size businesses (SMB) with a cost-effective storage consolidation and management solution where ease of integration, flexibility, and price/performance are paramount.

Mark Woithe is director of IP Storage Marketing at Xiran, a division of SimpleTech (Irvine, CA)

www.xiran.com