Storage Networking Building Blocks

Mar 8, 2002

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IP SANS: A Guide to iSCSI, iFCP, and FCIP Protocols for Storage Area Networks: A Guide to iSCSI, iFCP, and FCIP Protocols for Storage Area Networks

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3.7 Chapter Summary

Storage Networking Terminology

RAID provides performance and data redundancy.
RAID 0 stripes data blocks over multiple disks.
RAID 1 provides data duplication (mirroring) between two disks.
RAID 5 provides striping of data blocks and distributed parity for data reconstruction in the event of failure.
RAID levels may be combined—for example, RAID 0 + 1.
JBODs are more economical than RAID but have no inherent redundancy or mirroring capability.
To maximize performance, software RAID on host systems can be applied against JBOD targets.
Tape subsystems may be SCSI, Fibre Channel, or Gigabit Ethernet interfaces.
Bridge products can bring legacy SCSI devices into an IP-based SAN.
SAN host adapters may include Fibre Channel HBAs and IP storage NICs.
IP storage NICs may provide optimized logic for TCP off-loading.

Legacy SCSI Cabling

SCSI cabling provides parallel wires for simultaneous transfer of data bits.
The maximal SCSI cabling is 25 m.
The maximal device population for SCSI cabling is 15 devices on a string.
Skew refers to the window of time required to capture all data bits in a parallel transmission.

Network-Attached Storage

NAS serves files; SANs provide data blocks.
The NAS architecture is comprised of a thin server and attached storage.
NAS storage may be ATA, SCSI, or Fibre Channel.
NAS uses NFS or CIFS over IP for file access.
NAS products are typically marketed as appliances, requiring little configuration or management.
NAS and IP-based SAN traffic may share a common network infrastructure.

Fibre Channel

Fibre Channel is a standards-based, layered architecture.
FC-0 defines gigabit physical layer specifications.
FC-1 provides data encoding and link-level controls.
FC-2 defines segmentation and reassembly of data via frames, flow control, and classes of service.
FC-3 is being developed for common services such as encryption.
FC-4 is the upper layer protocol interface between Fibre Channel and IP, SCSI-3, and other protocols.
The most commonly used FC-4 protocol is FCP for serial SCSI-3.
FC-0 and FC-1 provide the foundation layers for Gigabit Ethernet.
The 8b/10b data encoding algorithm coverts 8-bit bytes into 10-bit characters.
Encoding is required to prevent sustained DC states on the gigabit link.
A proportional representation of ones and zeros is maintained via running disparity.
Ordered sets are 10-bit characters used for frame delimitation, signaling, and link change notification.
The maximal payload for a Fibre Channel frame is 2,112 bytes.
The most commonly used class of service for Fibre Channel is class 3, which is connectionless and requires no acknowledgment of frame receipt.
Fibre Channel has no standardized encryption or authentication methods.
FCP is responsible for mapping SCSI devices at the operating system level to Fibre Channel-attached storage resources.
Fibre Channel topologies include point to point, arbitrated loop, and fabric.
Fibre Channel fabrics use a subset of OSPF called FSPF for fabric routing.
The Fibre Channel fabric appears as one integral network.
Interoperability and management issues for fabric switches have retarded the deployment of Fibre Channel SANs.

Gigabit Ethernet

Gigabit Ethernet is a data link transport that borrows from both Fibre Channel and conventional 802.3 Ethernet.
Ethernet framing is used to transport TCP/IP data over Gigabit Ethernet networks.
802.1Q VLAN tagging allows segregation of devices on the SAN.
802.1p/Q frame prioritization enables mission-critical traffic to be assigned one of eight levels of priority for SAN transport.
802.3x flow control provides reliable transport of storage data over connectionless protocols such as UDP/IP.
802.3ad link aggregation allows scalability of IP-based SANs with no loss in performance.
Gigabit Ethernet's transmission rate of 1.25 Gbps provides slightly better performance than Fibre Channel.
Gigabit Ethernet cabling includes category 5 unshielded twisted pair copper cabling as well as standard multimode and single-mode fiber-optic cabling.

Assumptions for IP-Based SANs

Storage networks based on IP and Gigabit Ethernet can leverage new functionality for class of service, VLANs, flow control, and trunking provided by Ethernet standards.
An optimal storage over IP solution accommodates legacy SCSI, Fibre Channel, and native IP storage devices.
Management of storage networks requires the integration of transport management and storage management.
Interoperability is a key driver for market adoption.

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