Make the Most of Your SAN with iSCSI

Executive Summary: Fibre Channel is still the transport of choice for many data centers with high bandwidth and high availability requirements. However, iSCSI is a mature storage technology and is being deployed for small departmental operations as well as data center applications. Combining iSCSI and Fibre Channel Storage Area Network (SAN) technologies helps administrators bring all server assets into a common storage infrastructure. Microsoft iSCSI Software Initiator and Microsoft iSNS Server are free software applications that let Windows servers participate in a combined SAN.

Modern data centers typically run their most mission-critical business applications on Fibre Channel SANs. Fibre Channel has a proven track record in enabling fast performance and high availability of application data as well as established best practices for data backup and disaster recovery. Not all business applications, however, require the bandwidth of 4Gbps Fibre Channel, and large data centers might have hundreds of second-tier standalone rack-mounted servers still using direct-attached storage. Some find it hard to justify the cost of a $1,000 Fibre Channel host bus adapter (HBA) when the server itself cost less than $3,000. On the other hand, standalone servers incur more administrative overhead per server, particularly for backup operations.

Until the advent of iSCSI, there were few options for economically integrating all application, Web-hosting, and file servers into the data center SAN. iSCSI and iSCSI gateways, however, now provide the means to streamline the management and backup of second-tier servers and integrate these servers into the Fibre Channel SAN. This integration extends data center best practices to all server assets and can amortize the substantial investment in a data center SAN over a much larger population of attached devices.

Microsoft offers new iSCSI-enabling software, making it possible to cost effectively bring Windows servers into the data center. Let's look at the steps required to make this happen and factors you need to consider. First—a little background on iSCSI.

Using economical Gigabit Ethernet interface cards and Gigabit Ethernet switches keeps the iSCSI per-server attachment cost low and works fine in many situations. Some vendors do provide iSCSI HBAs that optimize iSCSI processing via TCP offload engines (TOEs) and onboard iSCSI processing logic. iSCSI HBAs are required for boot from SAN applications, and they're suitable for applications that require high bandwidth, but they increase per-server attachment costs. In this article, I assume standard Gigabit Ethernet NICs. With the faster 10 Gigabit Ethernet, you lose most of the cost advantage over Fibre Channel.

For Windows storage management, an iSCSI target appears as just another storage resource that can be assigned a drive letter, formatted, and used for applications and data. Instead of being housed inside the server or connected by parallel cabling, though, the iSCSI storage resource can be anywhere in an IP-routed network. Because iSCSI is a block storage protocol, the latency of long-distance connections over a WAN might have a serious negative effect on performance or cause timeouts. Typically, iSCSI is best deployed within a data center, campus, or metro environment.

Microsoft iSCSI Support
Microsoft's introduction of iSCSI initiator and Internet Storage Name Service (iSNS) software provides an economical means to bring even low-cost Windows servers and workstations into the data center SAN infrastructure. Microsoft iSCSI Software Initiator enables connection of a Windows host to an external iSCSI storage array. Microsoft iSNS Server discovers targets on an iSCSI network.

As of this writing, iSCSI Software Initiator =2.04 is available free on the Microsoft Download Center and requires Windows Server 2003 or later, Windows XP Professional SP1 or later, or Windows 2000 SP3 or later. Download it at http://www.microsoft.com/downloads/details.aspx?familyid=12cb3c1a-15d6-4585b385-befd1319f825&displaylang=en. Microsoft iSNS server code is also available as a free download and requires Windows Server 2003 or Windows 2000 SP4. Download it at http://www.microsoft.com/downloads/details.aspx?familyid=0dbc4af5-9410-4080a545-f90b45650e20&displaylang=en.

Microsoft has included some attractive features in iSCSI Software Initiator, including multipathing, security, and support for server clustering to iSCSI targets. Multipathing with the Microsoft Multipath I/O (MPIO) driver included in iSCSI Software Initiator provides for higher availability through failover and better performance through load balancing. Secure connections between iSCSI initiators and storage targets are supported with Challenge Handshake Authentication Protocol (CHAP) and IPsec for data-payload encryption. Authentication and encryption might be required when storage data traverses an untrusted network segment. Support for clustering enables iSCSI storage to be used for Microsoft Exchange Server or Microsoft SQL Server clusters. For the configurations discussed below, the Exchange or SQL Server data can be managed centrally and protected on the SAN, while clustering provides high availability of applications to end users.

iSNS Server isn't mandatory, but it does simplify iSCSI deployment by enabling automatic discovery of iSCSI target resources. It can be run on a dedicated server or coexist with other server applications. Essentially, iSNS Server combines the capabilities of DNS with conventional discovery services provided by the Simple Name Server (SNS) of Fibre Channel fabrics. In Fibre Channel switches and directors, for example, the SNS contains information about all storage assets in the SAN. As a storage array or tape subsystem is attached to the SAN, it registers with the SNS. When Fibre Channel initiators connect to the fabric, they query the SNS for available storage resources. The resources that are reported to a specific initiator can be filtered by use of zoning and LUN masking. This prevents initiators from accessing unauthorized storage assets (e.g., stopping a Windows server from binding to a UNIX storage array).

Because Fibre Channel connections today are typically 2Gbps or 4Gbps and iSCSI is typically 1Gbps, you can aggregate more iSCSI servers per Fibre Channel storage port on an iSCSI gateway than you can Fibre Channel servers. In conventional business application environments running at 1Gbps end to end, a typical ratio of servers to storage ports (known as the fan-in ratio) might be 7:1. An iSCSI gateway that provides 1Gbps port connections for iSCSI initiators and 4Gbps connections for storage ports can enable a much higher fan-in ratio of 18:1 or greater. For iSCSI initiators, you implement the higher fan-in ratio by attaching multiple iSCSI servers to a Gigabit Ethernet switch, which in turn provides a 1Gbps connection to the iSCSI gateway for every fan-in group. An iSCSI gateway that offers four 1Gbps Ethernet ports and several 4Gbps Fibre Channel ports can support 70 or more iSCSI initiators concurrently.

   Previous  [1]  2  3  Next