Intelligent Storage:The Big Picture

As traditional storage strategies become increasingly inadequate, new alternatives are rising to the challenge

By Arun Taneja

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Storage Planning for the Future

Trends to keep your eyes on Several new technologies that will influence your storage decision are on the horizon. They include: iSCSI. To counter the limitations of FC, the storage vendor community, led by Cisco Systems and IBM, is presently defining a protocol that would let block-level SCSI traffic move over existing TCP/IP networks. This technology is hugely important in that it simplifies moving to SANs. Because enterprises already have TCP/IP networks, IT talent with TCP/IP knowledge is more readily available, so the theory is that implementation with iSCSI will be easier and more cost effective. I believe this theory is indeed true. However, iSCSI standard is not completed yet (expect late 2001) and several large issues still remain unresolved. While some products have started to appear in the market, they will not be ready for deployment in mission-critical environments until mid 2002, in my estimation. InfiniBand (IB). Yet another standard being proposed by Intel, Sun, Compaq, HP, Dell and others, InfiniBand - originally targeted at replacing the aging PCI bus - now appears to have more grandiose plans. It is essentially a switch-based (vs. PCI, which is a shared bus) protocol that would let CPUs connect with other CPUs and I/O devices at very high speeds. The initial spec is for 200MBps. I believe IB will play a role in server-to-server clustering but not necessarily as a complete replacement for FC or iSCSI SANs. Initial products are due toward the end of 2001. IB is definitely a technology worth watching. Storage Virtualization (SV). This technology is crucial to make SANs based on FC, iSCSI, or IB real. Effectively, storage virtualization makes disparate storage devices in a SAN look like one big, logical pool of storage that can be securely "sliced and diced" and allocated to servers as needed. It simplifies storage applications, such as remote mirroring, disaster recovery, backup and restore, and makes managing storage significantly easier. Products are available now. If you want to implement heterogeneous FC SANs today, you will need SV. Serverless backup. Backup is the number one issue for the enterprise IT community today. Given the nature of the Internet economy, you have no backup windows left, yet backup is still necessary for business survival. Serverless backup is a technology that is just reaching prime time. It lets backup happen over the high-speed FC SAN, with negligible impact on the servers. Thus, servers can continue to serve applications without degradation while the data remains protected. This technology is a must for a well-designed storage infrastructure.

New Infrastructures

Two storage infrastructures have arrived on the scene recently: network attached storage (NAS) and storage area network (SAN). I will first discuss these conceptually and then look at the technologies that lie underneath, with their pros and cons.

Network attached storage. Conceptually, you can think of a NAS device as a dedicated file server that is attached to the network - typically Ethernet - and serves files to a multitude of clients on that network. NAS provides common storage for needed files that a large number of heterogeneous clients can access. The most common access protocols are NFS (often used by Unix clients) and CIFS (used by Windows clients). In the mid-1980s, general-purpose Unix servers played the role of a file server in addition to performing other tasks, such as application and database management. Then in the late 1980s, Network Appliance Inc. developed the concept of an appliance, a system designed to perform only one function, in this case file serving, that was significantly better in terms of performance and management than a general purpose server.

While the terminology for NAS came later, this appliance was indeed a NAS box. It connected via Ethernet and had vast amounts of storage expandability for its time, and because it required little or no configuring, it could be put into service within minutes. The role of NAS had been increasing steadily, but has reached a crescendo due to the maddening pace of data growth. Already at $2 billion, I expect the NAS market to grow at about 70 percent for the next few years. The two major players are Network Appliance Inc. and EMC Corp. Other server vendors (Compaq Computer Corp., Dell Computer Corp., Hewlet-Packard, Sun Microsystems, and so forth) have also jumped into the fray.

Besides excellent performance and ease of management, the most notable aspect of NAS is the fact that it deals exclusively with file-level rather than block-level data (explained later in this article).

Storage area network. Conceptually, a SAN's primary purpose is transferring data between computer systems and storage units, or between storage units. While there is no theoretical tie between a SAN and Fibre Channel (FC) protocol, in reality the terms are used interchangeably today. With the advent of InfiniBand and iSCSI protocols, this association is bound to change (see the sidebar, "Storage Planning for the Future," for an explanation of terms).

Figure 2 shows a simple SAN based upon FC protocol. In effect, I have stripped the servers of all storage units, created an FC network on the other side of the TCP/IP-based Ethernet network, and connected all the servers via high-speed 100MBps links to an FC switch, to which I have attached FC disks and a tape library via an FC-SCSI bridge. This configuration lets us consolidate storage and independently scale storage and servers, based upon requirements rather than architectural limitations. You can allocate portions of storage to a given server and reallocate as necessary by simple drag-and-drop methods. All storage is managed as a common pool, easily increasing the amount of storage managed by an administrator by factors of 5 to 10. You can interconnect the switches into a fabric and scale them almost infinitely, hence providing incremental bandwidth as you need it. This storage networking concept lets the bandwidth, performance, and capacity scale independently along the three axes. Application servers can then increase their performance for application processing because they no longer have the burden of storage management. Your TCP/IP network congestion has relief as most data now travels on the high-speed SAN. You can share tape resources and enhance backup and restore efficiency. Cumulatively, these are huge benefits.

A key aspect of a SAN is that it deals with block-level data. To understand this data attribute requires a quick understanding of SCSI - a protocol used by a computer to talk to a storage device. The transfer of data between these devices occurs in chunks known as "blocks." Certain applications, most notably database applications, use this method of communicating with a disk in order to maximize performance. Consequently, some of the earliest SAN implementations have been for database applications (financial, e-commerce, CRM, ERP, and so on).

For reasons already stated, the SAN market is already at a $5 billion level and is expected to grow at 50 percent or more over the next few years.

NAS vs. SAN. A hot debate is brewing in the market regarding the superiority of one technology over the other. But - in a nutshell - the debate is completely useless. Both technologies are required to alleviate the issues of storage growth and management. As shown in Figure 3, it is only a matter of time before most solutions in the market will let you store all data in a common storage pool, with access to this data via block or file - depending upon the application and user needs. Figure 3 shows an Internet application where you need both NAS and SAN to get the job done. Also bear in mind that even NAS devices that connect via Ethernet on the front end, often have their back ends connected via SAN, to the disks. All of these situations should lead you to one conclusion: Both are necessary in spite of what vendors tell you. Storage networking is the term that encompasses both NAS and SAN and captures the essence of storage and networking convergence. I prefer this term as well.

Your application determines which of these two methodologies will be most appropriate. For instance, a financial application that deals with transactions (OLTP application) will benefit from a SAN, and the database behind the application is most likely designed to handle block-level data. An email application, on the other hand, deals with files so a NAS device would be most effective. You can establish very quickly that a typical enterprise has applications that span across NAS and SAN boundaries and therefore, requires a well thought-out storage strategy to smoothly incorporate both. (See Table 1.)