RapidIO Connections Newsletter - Spring 2005
Design It:RapidIO® Interconnect Technology in Storage The challenge of successfully managing more data more easily is central to the professional existence of today’s IT manager. Both data storage capacity and data storage creation are growing at tremendous rates. According to a U.C. Berkeley Information Study 2003, “Print, film, magnetic, and optical storage media produced about 5 exabytes (260) of new information in 2002. Ninety-two percent of this new information was stored on magnetic media, mostly in hard disks.” A good example of a typical storage system architecture is the EMC MOSAIC: 2000 architecture.
This architecture is comprised of a group of front-end processors referred to as channel directors,
a large data cache and a set of back-end processors, referred to as disk directors. (see Figure
1.0) The front-end processors manage the communications between the host computers and the storage system. The back-end processors manage the communications between the storage system and the physical disk drives. The cache memory is used to retain recently accessed data and to provide a staging area for disassembling data to be sent to multiple physical drives. In addition to the transfer of all the data, there is also a translation of protocols. The host connections will often be accomplished by a networking interface such as IP operating over Ethernet or Fibre Channel. The interface to the physical drives might be Serial ATA or SCSI. Each interface has its own packet or frame. The ‘storage matrix’ is actually a collection of channel directors, cache memory and disk directors. Within the ‘storage matrix’ is a ‘physical matrix’ that is the actual collection of physical disks and connectivity in the system. However, the ‘physical matrix’ will not typically be found on an optimal representation of storage to the host computers. For this reason the storage system will always provide a ‘functionality matrix’ view to the host computers. This functional view can be quite different in character from the actual physical characteristics of the storage. A data storage system has various important features. The first and most obvious is sheer capacity. Another very important aspect of data storage is data integrity. This can be translated into at least two very important criteria, availability and reliability. Another is density, the need to be as efficient and as low power as possible. Of course, manageability is another key factor, especially ensuring that the cost of managing storage doesn’t exceed the cost of storage itself. The RapidIO architecture was designed to address the need for high-performance interconnects in embedded systems. Earlier, the ‘physical matrix’ of storage was presented. This ‘physical matrix’ is composed primarily of a high-density matrix of CPUs, cache memories, IO devices and the connectivity to tie all of these devices together. In this section, the attempt is made to correlate the major connectivity requirement of storage with the characteristics of RapidIO.
RapidIO is a well-developed system interconnect and fabric standard. It has been designed from the ground up with cost, performance and reliability in mind. The strong correlation between the technology needs of enterprise storage systems and the characteristics of the RapidIO interconnect technology has been demonstrated. RapidIO is an obvious candidate technology for providing the system connectivity for today’s distributed, high-availability, fault-tolerant storage systems. Excerpted and condensed from RapidIO The Embedded System Interconnect by Sam Fuller, John Wiley & Sons, Ltd., 2005, Chapter 13. |
