When iSCSI was launched, Fibre Channel was well-established as a high-performance SAN solution. It seemed obvious, therefore, that iSCSI would appeal to IT environments that chose not to move to a SAN: either direct-attached storage environments that previously didn’t need SANs, or environments that had rejected Fibre Channel for some reason.

Also, Fibre Channel SAN environments were mostly tier-1 and tier-2 data centers running primarily Unix systems, so iSCSI first got traction in Windows and Linux environments. Supporting this further, Windows applications were increasingly viewed as mission critical through the last decade, driving the need for networked storage instead of direct-attached storage.

Another consideration, obvious in hindsight, is that the availability of full-featured software initiators drove end-user adoption of iSCSI. This happened first with Windows, and more recently with VMware.

Today, typical host/OS environments for iSCSI include:

  • Intel-architecture servers
  • Windows, or Windows with some Linux or Unix
  • Virtual server environments — mostly VMware, with some Xen and Hyper-V


This may change over time, as virtual server environments become dominant, but Windows will continue to be the sweet spot for iSCSI, followed by Linux and Unix.

iSCSI has become a popular SAN solution in both large organizations and SMBs. Deployments in large enterprises have typically been in tier-2 and tier-3 data centers and large remote offices. In SMB environments, it is common to see iSCSI SANs in both primary and secondary data centers and in remote offices.


Another sweet spot for iSCSI is in application service provider environments. NFS-based NAS running on a high-performance Ethernet fabric often dominates here because most traffic is file-based, but iSCSI adds seamless support for applications that benefit from SANs. These are now evolving into cloud computing environments, as virtual server software is added.

The application sweet spot for iSCSI has been storage consolidation for business-critical Windows environments. iSCSI’s popularity has been fueled not only by the fact that it provides affordable SAN storage, but also by the fact that even entry-level iSCSI disk arrays often include sophisticated data-management capabilities such as point-in-time copy, remote copy, LUN cloning and asynchronous mirroring. These features enable IT organizations to significantly improve provisioning and backup/recovery, while reducing infrastructure and administrative costs.

Deployment Considerations

In an iSCSI SAN, host systems are provisioned with iSCSI initiators – typically software initiators. Also, a separate IP network or VLAN for storage traffic is recommended, configured with redundant connections supporting host multi-pathing. Turning on jumbo frames is also a best practice, as it improves performance (15% to 20% is typical). Single or multiple 1GbE connections are still the dominant connection type, although 10GbE has ramped up in the past year to account for more than 10% of the total connections.

LUN provisioning is very straightforward with iSCSI. LUNs and virtual server instances are provisioned, and LUNs are mapped to individual virtual servers. LUN masking and iSCSI authentication provide security. Often, a secondary remote environment is set up, and array-based mirroring is configured to support data recovery and virtual server fail-over and recovery in the case of a failure at the primary site.

A variety of tools exist for data migration to new virtual server environments. In addition, either host-based or array-based snapshots integrated with the host environment can be used for fast backup and recovery of data and/or virtual servers. In addition, LUN cloning enables rapid provisioning of virtual servers.

The resulting environment provides improved storage and server utilization, a reduction in administrative overhead, fast backup and recovery, fail-over and continuous operation in the case of a disaster, rapid recovery in the case of application failure, and fast application provisioning for test and development and software upgrades. Advanced capabilities such as thin provisioning are available on both the host virtual server and on iSCSI arrays, further enhancing utilization and recovery. In addition, data deduplication, if available on the disk array, can make a considerable difference in the amount of disk space required.

iSCSI Market Share

According to market researcher IDC, iSCSI has consistently grown faster than the overall networked storage market.

In terms of revenue growth, IDC estimated that the iSCSI market would grow 58% in 2009, vs. 17% for the overall networked storage market. And in terms of capacity growth, the iSCSI market was expected to surge 117% in 2009, vs. 90% for the total networked storage market.

Through the third quarter of 2009, iSCSI accounted for about 13% of revenues in the networked storage market, with Fibre Channel accounting for 61% and NAS for 26%.

In terms of capacity, iSCSI accounted for 15% of the networked storage market, with Fibre Channel SANs at a 52% market share and NAS with the remaining 33% of the market.