iSCSI: changing the storage landscape

Computer Technology Review,  Sept, 2004  by Steve Rogers

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In today's ever-expanding business model, more and more information and applications are being housed outside the corporate data center as companies struggle to store, protect and provide access to an ever-increasing amount of data throughout the enterprise. While direct attached storage (DAS) has been the dominant storage model for servers, there has recently been a strong movement toward networked storage technologies (such as the new standards-based Internet Small Computer System Interface (iSCSI) technology), which have the potential to significantly increase the proliferation of affordable networked storage.

Companies that have had a DAS infrastructure for many years are discovering that these legacy systems have become a business issue. While older servers' computing capability might be adequate, their storage subsystems may be obsolete, due to lack of expandability or aging reliability. While DAS often works well in environments with a limited number of servers, significant data growth can quickly make the situation unmanageable. The only way to accommodate growth is to add servers; yet since each server must be managed individually, every additional server increases management expense and difficulty.

The inherent inflexibility of DAS makes it difficult to deal with unplanned growth; it is tough to scale, and unused resources cannot be redeployed. This often leads to under-utilized, over-provisioned resources, leaving departments and enterprises with large amounts of unused capacity that might be needed someday.

While traditional Fibre Channel storage area networks (SANs) overcome a number of the issues posed by DAS, they are expensive to implement and maintain. Network attached storage (NAS) has traditionally provided cost-effective file data storage, but has limited applicability in applications--such as databases--where DAS typically resides. However, the emergence of standards-based iSCSI technology offers the benefits of a SAN with the cost-effectiveness of NAS over an existing Gigabit Ethernet IP network. The cost, flexibility and efficiency of this new class of IP SANs offer some compelling business reasons for moving to this storage architecture.

The creation of an IP SAN requires host application servers equipped with an iSCSI initiator driver; a standard Gigabit Ethernet NIC, TOE card, or iSCSI initiator HBA; an Ethernet switch; and an iSCSI storage target. The iSCSI protocol is a client/server model, whereby an iSCSI initiator initiates requests and an iSCSI target receives the requests and delivers the requested data. The iSCSI stack at both ends encapsulates SCSI commands and block data for transmission over TCP/IP.

By separating the storage from the server, an IP SAN allows flexible storage to reside anywhere on the network and, under certain circumstances, can provide access to that block-level data from multiple servers.

In traditional storage scenarios, different storage devices had to be deployed for different access topologies: one for corporate applications that require access to block data, and another for file access using CIFS/NFS network file-sharing protocols. With iSCSI's ability to transfer block data over an IP network, both files and block data can be centralized on a single storage server. This "unified block and file" architecture provides the benefit of SAN-style block-level storage at speeds that are acceptable in many applications, and greater reliability, at a significantly lower cost.

Physically consolidating storage in an IP SAN centralizes storage management, making it possible to manage one storage server or every storage server on the network from a single location. IP SAN storage devices can be increased with expansion disk arrays and the capacity of existing volumes can be expanded, usually without requiring downtime or RAID rebuilds. Storage can be provisioned as needed.

In terms of availability, iSCSI storage volumes behave like dedicated local storage with underlying RAID for added data protection and redundant hardware to minimize downtime.

IP SANs:

* Are easy to use, deploy, and understand

* Improve storage utilization, scalability, and availability

* Connect with standard Ethernet hardware and existing plumbing

* Have the lowest initial investment of any SAN solution

* Offer the lowest TCO of available storage topologies

Whether replacing a legacy DAS system or as an adjunct expanding the capacity of existing servers, an IP SAN built on iSCSI standards can provide advantages to many applications throughout an enterprise. Examples include:

* Saving Microsoft VSS shadow copies on an IP SAN instead of on the Windows server provides fast, user-accessible file/folder recovery, and easy access to previous versions while reducing demand on IT.

* For Microsoft Exchange archive applications, an IP SAN provides fast, economical block storage and recovery without the cost and complexity of clustered or proprietary solutions.

* Storage consolidation using IP SAN can extend the life of aging servers by adding capacity and providing extremely cost-effective and scalable block storage for back office, small and medium business, retail operations, and departments.