Pros and cons of iSCSI for SMBs

The introduction of iSCSI has started a shift in SMB storage. This article discusses the benefits of iSCSI for SMBs and how to make it work.

Small and medium-sized businesses (SMB) have stayed away from SAN implementations in the past because of the expense and complexity of Fibre Channel technologies. However, the introduction of iSCSI has started a shift in SMB storage. The use of Ethernet translates to lower cost, easier maintenance and simpler management for SANs. Today, SMB users can run block-based applications, such as databases at performance levels that rival Fibre Channel SANs.

Benefits of iSCSI for SMBs

Although it is possible to construct an expensive iSCSI SAN, low cost is the biggest benefit for SMB users. Virtually all LANs are based on TCP/IP (Ethernet), which is easy to obtain, install, configure and upgrade throughout the SMB. In fact, an iSCSI SAN can be implemented on the existing Ethernet LAN, though that's usually not a good choice to support high-performance applications; it increases the risk of a security breach. In addition, Ethernet is the standard for global connectivity, allowing communication and data transfers across the Internet. This makes it possible to transfer or backup iSCSI SAN data between remote locations without expensive Fibre Channel protocol converters or high-bandwidth connections.

Low cost also means that an SMB can create large iSCSI SANs, potentially incorporating every host or storage server in the business. This avoids the frequent enterprise problem of forgotten storage or "storage islands" -- collections of storage servers that are just not quite important enough to justify the expense of Fibre Channel host bus adapters (HBA) or switch ports.

With Fibre Channel SANs, storage administrators must be versed in Fibre Channel architecture -- a specialised area of expertise. The cost to hire (or train) employees to manage a Fibre Channel environment is typically too great for most SMBs. By contrast, Ethernet setup and configuration is a well understood process that many individuals tackle successfully in their own homes.

Making iSCSI work for the SMB

When it comes to deployment, iSCSI considerations are identical for SMB and enterprise users alike. Businesses that choose to embrace iSCSI should start with a 1 Gbps LAN. Older 10/100 Mbps Ethernet LAN components are typically not suited for iSCSI SAN use. This may require refitting older Ethernet network interface cards (NIC) and switches for 1 Gbps operation.

Once the LAN itself is updated to an appropriate speed, it's important to isolate iSCSI traffic from the production LAN. Isolation prevents iSCSI traffic from congesting the everyday network, and it also keeps sensitive data away from everyday LAN users. This is a critical security measure -- data "leakage" out of the SAN (and possibly out of the business) can be devastating for a company of any size. SMBs should also rely on access controls, such as CHAP, to limit iSCSI SAN access to authorised personnel only.

ISCSI SAN data is frequently carried on the same physical LAN, but it is channelled through a VSAN that keeps the SAN data logically separated from user data. However, the SMB may choose to build a small Ethernet LAN for iSCSI SAN use, incorporating high-performance parts, such as TOE cards and iSCSI storage switches. If higher availability and resilience is needed, and cost is not a factor, investigate the possibility of using multiple TOE cards and iSCSI switch ports for aggregation and failover tasks.

Since iSCSI runs on top of an existing Ethernet network, often competing for available bandwidth with user traffic, the network design is extremely important to iSCSI performance. Network interruptions due to congestion bottlenecks can potentially crash an iSCSI storage array. SMBs are particularly sensitive to this because their networks are rarely optimised and bandwidth is limited. So, any foray into iSCSI technology should include a careful evaluation of the existing network, and traffic bottlenecks between the hosts and storage systems should be corrected before critical data is stored.

Software-based initiators are used in 90% to 95% of all iSCSI deployments implemented on top of an existing Ethernet LAN. SMBs usually don't require the added performance afforded by TOE cards and switches. However, it's important to use stable and mature initiators, such as the free iSCSI initiator software that is already available for download with Windows 2000, 2003 and XP Pro.

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