By Andrew Gilman
In today's uncertain economic environment the natural tendency is to spend less and save more, especially in the data center. However, IT organizations that accelerate investments in technologies such as server virtualization and storage virtualization will be positioned to emerge successfully from this economic downturn.
Both server and storage virtualization significantly reduce operational expenditures, enabling businesses to quickly recover their investment. However, one barrier to deploying a fully virtualized data center is leveraging storage consolidation technologies, largely because it can be an overly complex and expensive undertaking requiring proprietary infrastructure, expensive add-on software, and highly skilled specialists.
For virtualized IT environments, storage consolidation through SANs is required to enable advanced virtual server capabilities, such as high availability and online migration of virtual machines (VMs). Advances in IP storage virtualization help overcome the challenges of SAN deployment and therefore enable organizations of all sizes to cost- efficiently implement virtualized IT infrastructures.
There are a number of reasons why IP storage networking is being widely deployed, including reduced acquisition, deployment, training, service, maintenance, and ongoing operating costs.
Back to basics
iSCSI is a storage access protocol for interconnecting servers and storage using an IP-based network interconnect. The protocol is built upon the SCSI and TCP/IP protocols, and leverages an organization's existing network infrastructure.
Software-based iSCSI initiators, available for all major operating systems at minimal or no cost, take advantage of standard Ethernet interfaces on servers and desktops.
Using an IP network, iSCSI transports block-level data between an iSCSI initiator on a server and an iSCSI target on a storage device. The iSCSI protocol encapsulates SCSI commands and assembles the data into TCP/IP packets sent over the network using a point-to-point connection. Upon arrival at the storage device, the encapsulated SCSI commands are unpacked from the TCP/IP packet for processing.
When an iSCSI initiator connects to an iSCSI target, the storage is seen by the operating system as a local SCSI device that can be formatted as usual. The process is transparent to applications, file systems, and operating systems. By consolidating storage with an iSCSI SAN, multiple platforms can share the same storage, improving utilization and efficiency.
Using standard Ethernet NICs to connect servers to storage makes iSCSI simple and affordable. Today's high-speed CPUs can run iSCSI at line speed over standard NICs using only a marginal amount of CPU cycles. Ethernet NICs come standard with servers, so no additional cost is incurred and special adapter cards are not required.
Together, standard NICs and inexpensive Ethernet switches offer cost savings over other SAN interconnects, while maintaining the performance advantages of a SAN. However, the savings are not limited to the hardware costs. With iSCSI, IT departments can utilize their existing IP networking expertise, without needing specially trained staff.
iSCSI and virtualization
Recently, virtual storage designs have evolved to leverage iSCSI. IT professionals generally define storage virtualization as a technology that allows discrete storage systems to operate as a single resource. In light of recent advancements in server virtualization, the concept of storage virtualization is being further refined as a way to create an abstraction layer between the storage hardware and logical data volumes.
Storage virtualization is similar to server virtualization in that it enables you to create an intelligent SAN infrastructure that is easy to manage and scale. Some storage virtualization designs leverage iSCSI features such as IP Redirect to enable simplified management and scalability.
Virtual storage allows data volumes to be located and striped across multiple (and diverse) physical resources, including disk arrays, RAID groups, drive types, and controllers. Not only can this provide high performance and scalability, it also allows data volumes to be transparently moved from one set of resources to another without disruption to the operating systems and applications utilizing the data.
Effective virtual server deployments depend on shared access to storage. SANs ensure that each virtual server has concurrent, fast access to any virtual machine's (VM's) data sets, enabling immediate re-hosting of the VM. This eliminates the time-consuming steps of copying VM files, applications, and data from one virtual server to another.
In addition to the requirement for networked storage, a virtualized environment increases the need for high performance, highly available storage to meet the requirements of workload aggregation. As more critical applications, production workloads, and data assets are consolidated into fewer resources, there is a greater need for high performance, non-disruptive scalability and continuous availability of storage assets.
In particular, storage architectures should include mirrored memory write caches, redundant hot-pluggable components, online hot-spare disks, environmental monitoring, and enterprise-class disk drives with RAID protection. In addition, advanced availability features, including storage controller and I/O path failover, are required to guarantee data access even in the case of component failure.
ANDREW GILMAN is on the SNIA ESF board of directors, and is the manager of virtualization solutions marketing in Dell's global enterprise solutions group. The Ethernet Storage Forum (ESF) is a marketing organization within the Storage Networking Industry Association focused on driving adoption of Ethernet-connected storage networking solutions. For more information, visit www.snia.org/esf.