Using Stratix GX Devices in Storage Switches
Current drivers in the storage market include: different storage and networking technologies, advances in storage and infrastructure bandwidth, and information growth. However, converging the two main types of storage networking — storage area network (SAN) and network attached storage (NAS) — is a challenging task for storage infrastructure vendors. Additionally, users want a virtualized storage repository where they can view and manage all storage assets regardless of technology implementation (NAS or SAN), physical location, and various vendor brands. These demands push designers of storage switches to create more flexible and highly integrated systems. Stratix™ GX devices provide up to 20 transceiver channels, enabling designers to use a flexible and integrated solution on the line side and on the backplane with traffic management.
System Overview
Storage systems are storage farms that contain hard disk drives, redundant arrays of independent disks (RAIDs), controllers, and storage shelves (see Figure 1). The tape automation system (composed of backup libraries) provides duplicates of data in storage systems using the tape medium. These libraries have between 2 and 64 tape drives and can accommodate hundreds of tape cartridges. Director core switches are high port-count (64 to 512 ports) switches that control the data flow to and from the main data centers. Director core switches have high availability features such as redundant power supplies, processor boards, and multi-path connections to eliminate any single point of failure.
Figure 1. Storage Networking System Overview
Director switches contain multiple cards that are plugged into a backplane. The cards are either port (line) cards, switch fabric cards, or control cards. The backplane is used to route the signals to other cards that are plugged into the system. Some chassis can have cards that plug in at the front and in the back of the box. In this case, a mid-plane is used to route the signals to the cards in the box. The number of cards varies from vendor to vendor.
Using Stratix GX in Storage Switches
The port modules (line cards) in storage switches support multiple ports. These are typically Fibre Channel ports for Fibre Channel switches or Ethernet ports for NAS or Internet protocol (IP) storage switches. Figures 2 and 3 illustrate how Stratix GX devices can be implemented on typical port module cards for Fibre Channel and multi-protocol switch cards.
Fibre Channel Port Card
Fibre Channel is a data transfer interface technology that maps several common transport protocols, including IP and SCSI, allowing it to merge high-speed I/O and networking functionality in a single connectivity technology.
The basic data flow on a Fibre Channel port card is shown in the functional blocks of Figure 2. Gigabit interface converters (GBICs) convert the optical to electrical signals at the line interface. The data is then passed to devices that handle FC-0 through FC-2 layer functionality such as encoding/decoding, framing, flow control, service classes, traffic management, and queue/buffer management. Current systems use a mix of ASICs, ASSPs, and FPGAs to handle these data path functions. Fibre Channel is an evolving protocol, and FPGAs provide flexibility and an opportunity to provide differentiating services beyond those called out in the protocol.
Stratix GX devices can be used for the backplane interface and traffic management functions for the Fibre Channel storage line card shown in Figure 2. While current systems use proprietary backplane interfaces, several applications are moving to standardized interfaces, such as XAUI and InfiniBand. Stratix GX devices can also provide support for the Fibre Channel physical interface, PMA (FC-0) and transmission protocol, PCS (FC-1) for the single or multi-port Fibre Channel line card.
Figure 2. Fibre Channel Storage Line Card
FPGAs are currently used in the data path for processing Fibre Channel frames. This involves framing, flow control, and queue and buffer management. Stratix devices can be used for the framing and signaling protocol (FC-2).
iSCSI Line/Port Card
Functionality on an iSCSI port card is similar to that of line cards in the networking/access space. As such, the key functional blocks can be categorized into layer 1-2 functions for physical interfaces (PHYs) and media access controllers (MACs), layer 3-4 functionality for TCP/IP stack processing, IPSec, IP packet processing, traffic management, and queue/buffer management.
Stratix GX devices can also be used for the backplane interface and traffic management functions for the multi-protocol switch card shown in Figure 3. Stratix GX devices can support the physical layer (layer 1) electrical requirements for connection to the communications media, encoding/decoding, clock recovery, and data transmission and reception. The layer 3 (network) and layer 4 (transport) functions can be supported with Stratix devices.
Figure 3. iSCSI Switch Card
Notes to Figure 3:
- Layers ¾: Ipv4/Ipv6/TCP IPSec Packet Forwarding.
- TCP/IP Offload: link established/teardown, data transmission/reception, error handling, session timers.
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