Fiber Channel
Fiber Channel is a standard interface from the field of storage networks . The abbreviation of the associated protocol is FC-P .
overview
Fiber Channel is designed for serial, continuous high-speed transmission of large amounts of data.
Many storage area networks are now based on the implementation of the Fiber Channel standard. The data transfer rates achieved today are 4, 8, 16 and 32 Gbit / s, which is sufficient for data transfer rates of up to 3.2 GB / s in full duplex operation. However, lower data transfer rates are also possible. Until a few years ago, 1 Gb / s (1GFC) was the maximum data transmission rate in the Fiber Channel. Copper cables (mainly within storage systems; bridged up to 30 m) and fiber optic cables (mostly for connecting the storage systems to one another; bridged up to 10 km) are used as the transmission medium . Fiber Channel was developed to replace the old SCSI bus. The main application of Fiber Channel is the transport of SCSI commands, data and status. But there are many other so-called upper-layer protocols, such as B. SNMP, IP or virtual interface.
Similar to classic networks in which every network card has a MAC address , with Fiber Channel every device has a WWNN ( World Wide Node Name ) and every port per device has a WWPN ( World Wide Port Name ). It is a 64-bit value (usually shown in hexadecimal ) that uniquely identifies each Fiber Channel device. Fiber Channel devices can have more than one port, in which case the device still only has one WWNN, but it has the same number of WWPNs as it has ports. The WWNN and WWPN are usually very similar.
The expansion cards that enable the servers to communicate via Fiber Channel are known as host bus adapters (HBA for short). Typical HBAs require a PCI Express slot; older HBAs had a PCI-X slot with a 64-bit bus width and at least 100 MHz clock rate.
The payload (actually transferable data) of an FC frame is up to 2112 bytes, the protocol overhead is only 36 bytes (see iSCSI, TCP / IP without jumbo frames : 1460 bytes / 78 bytes; with jumbo frames 8960 bytes / 78 bytes). It is used to address and check the integrity of the data and consists of:
- Start of frame , 4 bytes: identifies the beginning of the data block
- FC frame header , 24 bytes: contains metadata about the block
- CRC , 4 bytes: checksum for checking the data integrity
- End of frame , 4 bytes: marks the end of the data block
Topologies
A general distinction can be made between three types of fiber channel topologies:
- Point To Point (FC-P2P),
- the simplest implementation in which two ports are directly connected to each other and thus only these two can communicate with each other.
- Arbitrated Loop (FC-AL),
- in which up to 127 ports are interconnected in a ring (or loop). Adding or removing a port means breaking the entire ring, and only one pair of ports can communicate with each other at a time. Even if such a ring only consisted of two ports, the differences in the protocol would be clear compared to an FC-P2P implementation. This topology can best be compared to a token ring network. FC-AL is also known as Low Cost Fiber Channel , it is often the entry point into the world of storage area networks . FC-AL implementations are often found in smaller clusters in which multiple physical nodes can directly access a shared mass storage device. This is where SCSI has reached its limit, which is why the Fiber Channel feature is used, which allows several hosts to be connected to several storage subsystems. All devices share the available data transfer rate (depending on the technology used, 133 Mbit / s to 4 Gbit / s) of the one available bus. Connecting the devices in series is also called daisy chain . If a fiber channel hub is involved, the cabling is mostly star-shaped, although the hub still creates a ring topology, in which a failed port no longer shuts down the entire ring ( port bypass circuit ). In an FC-AL, the N_Ports log in via the Extended Link Service Port Login (PLOGI).
- Switched Fabric (FC-SW),
- in which up to 24 ports can communicate with each other via Fiber Channel switches , very similar to a modern Ethernet infrastructure. In addition, many port pairs can communicate with one another at the same time. The Fiber Channel switched fabric is the most powerful and most resilient implementation of Fiber Channel . In most cases, switched fabric is meant when only fiber channel is mentioned. The fiber channel switch or director is at the center of the switched fabric . All other devices are connected to one another via this device, so that the Fiber Channel switch enables direct point-to-point connections to be made between any two connected devices. In order to further increase the data transfer rate, it is possible to install several HBAs in one server. After each N_Port of an HBA of the server has logged on to the switch with a fabric login (FLOGI) containing its WWPN and WWNN, the switch registers the host in the local name server with the WWPN / WWNN and a unique address consisting of DomainID ( Unique address of the switch in the fabric (see below), the port on the server, followed by 00 for switched fabric . This 6-byte address is used for addressing the port in the fabric . In addition, if several switches are used, they can be combined with one another ( fabric ). The switches then recognize the topology among each other and use it intelligently. In this way, the path with the least load is always used (FSPF - Fabric Shortest Path First ). If the server has more than one HBA and each HBA is plugged into a different switch, the server can thus reach a storage subsystem in several ways. This capability in Fiber Channel is known as multi-pathing . It increases the reliability and the performance of the Storage Area Network (SAN), since there is more than one possible data path between different devices. In order to further increase reliability, many fiber channel implementations have switched to working with redundant dual fabric . Two completely independent switched fabrics are operated, each storage subsystem and each server is connected to each of the two fabrics with at least one HBA . In addition to the failure of individual data paths, the overall system can even cope with the failure of an entire fabric , as there is no longer a single point of failure . This ability is particularly important in the area of high availability .
layers
Like the OSI and TCP / IP models, the Fiber Channel protocol stack is divided into layers. In contrast to these two, there are five layers, which can be compared as follows:
| OSI | TCP / IP | Fiber Channel |
|---|---|---|
| Applications | FTP, Telnet, SMTP, NFS, SMB, ... | FC-4 (Protocol Mapping Layer): SCSI, IP, FICON, ... |
| presentation | ||
| meeting | FC-3 (Common Services Layer): RAID, encryption, ... FC-2 (Network Layer): FC Core |
|
| transport | TCP, UDP, RSVP, ... | |
| Mediation | IP, ICMP, IGMP, ... | (no equivalent to the network layer) |
| Fuse | Ethernet, FDDI, Token Ring, ... | FC-3 (Common Services Layer): RAID, encryption, ... FC-2 (Network Layer): FC Core |
| Bit transfer | FC-1 (Data Link Layer): Line Coding FC-0 (Physical): Cable, plug, ... |
- FC-4 - In the Protocol Mapping Layer, application protocols such as B. SCSI or IP packaged in a protocol data unit so that it can be delivered via the FC-2 layer.
- FC-3 - Extended functions such as RAID protection or encryption can be implemented in the Common Services Layer .
- FC-2 - The Network Layer. Defined in the FC-PI-2 standard, it represents the actual core of the FC protocol.
- FC-1 - The data is converted into line signals in the data link layer.
- FC-0 - The physical layer that defines the cabling, connectors and connector types, etc.
The layers FC-0, FC-1 and FC-2 can be combined under the designation FC-PH as the physical layers of the fiber channel.
Fiber Channel routers work up to the FC-4 layer (i.e. they can function as SCSI routers, for example), switches up to FC-2 and hubs only on layer FC-0.
Fiber Channel products exist and were available in the speed versions 1, 2, 4, 8, 10, 16 and 20 Gbit / s. The 16 Gbit / s standard was approved by the INCITS T11 committee in 2010. FC products are only backward compatible for two generations; In other words , a 4 Gbit / s HBA can also handle 2 and 1 Gbit / s, while an 8 Gbit / s adapter no longer supports a 1 Gbit / s FC infrastructure. The 10 and 20 Gbit / s standards are special cases. They are not downward compatible with any other FC standard and are used practically exclusively for inter-switch link communication.
Port types in the fabric
| Abbreviation | Type | description |
|---|---|---|
| U_Port | Universal port | Start status |
| FL_Port | Fabric loop port | is connected to a loop |
| G_Port | Generic port | Preamp to E- or F-Port |
| F_Port | Fabric port | is connected to an N_Port |
| E_Port | Expansion port | Connection to another SAN switch |
| N_Port | Node port | Device is connected directly to the switched fabric (FC-SW) |
| NL_Port | NodeLoop port | The device is connected to an arbitrated loop (FC-AL) |
Cable lengths
| Data rate | cabling | Max. Cable length |
|---|---|---|
| 1 Gbit / s (1000 Mbit / s) |
Copper ( DE9 ) | 25 m |
| OM1 LWL-Multi Mode 62.5 / 125 µm | 300 m | |
| OM2 LWL-Multi Mode 50/125 µm | 500 m | |
| OM3 LWL-Multi Mode 50/125 µm | 860 m | |
| 2 Gbit / s (2000 Mbit / s) |
Copper (twisted pair) | 50 m |
| OM1 LWL-Multi Mode 62.5 / 125 µm | 150 m | |
| OM2 LWL-Multi Mode 50/125 µm | 300 m | |
| OM3 LWL-Multi Mode 50/125 µm | 500 m | |
| 4 Gbit / s (4000 Mbit / s) |
OM1 LWL-Multi Mode 62.5 / 125 µm | 70 m |
| OM2 LWL-Multi Mode 50/125 µm | 150 m | |
| OM3 LWL-Multi Mode 50/125 µm | 270 m | |
| OM4 LWL-Multi Mode 50/125 µm | 400 m | |
| 8 Gbit / s (8000 Mbit / s) |
OM1 LWL-Multi Mode 62.5 / 125 µm | 21 m |
| OM2 LWL-Multi Mode 50/125 µm | 50 m | |
| OM3 LWL-Multi Mode 50/125 µm | 150 m | |
| OM4 LWL-Multi Mode 50/125 µm | 190 m | |
| 16 Gbit / s (16000 Mbit / s) |
OM1 LWL-Multi Mode 62.5 / 125 µm | 15 m |
| OM2 LWL-Multi Mode 50/125 µm | 35 m | |
| OM3 LWL-Multi Mode 50/125 µm | 100 m | |
| OM4 LWL-Multi Mode 50/125 µm | 125 m |
The specification OM1-3 refers to the classification of the glass fiber. With 50/125 µm when wiring z. B. 1 Gbit / s OM2 fiber optic cables, first the diameter of the core, then that of the jacket. Compare fiber optics # fiber categories and areas of application and its sub-item for categories of multi-mode fibers
Fiber optic variants
| Media type | speed | Transmitter | variant | distance |
|---|---|---|---|---|
| Single mode fiber | 400 MB / s | 1300 nm long wave laser | 400-SM-LL-I | 2 m to 2,000 m |
| 200 MB / s | 1550 nm long wave laser | 200-SM-LL-V | 2 m to 50,000 m | |
| 1300 nm long wave laser | 200-SM-LL-I | 2 m to 2,000 m | ||
| 100 MB / s | 1550 nm long wave laser | 100-SM-LL-V | 2 m to> 50,000 m | |
| 1300 nm long wave laser | 100-SM-LL-L | 2 m to 10,000 m | ||
| 1300 nm long wave laser | 100-SM-LL-I | 2 m to 2,000 m | ||
|
Multimode fiber (50 µm) |
400 MB / s | 850 nm short wave laser | 400-M5 / 6-SN-I | 0.5 m to 150 m |
| 200 MB / s | 200-M5 / 6-SN-I | 0.5 m to 300 m | ||
| 100 MB / s | 100-M5 / 6-SN-I | 0.5 m to 500 m | ||
| 100-M6-SL-I | 2 m to 175 m |
Similar standards
- ATA over Ethernet : With ATA over Ethernet (ATAoE), ATA / ATAPI packets are encapsulated in Ethernet. Similar to FC, ATAoE is not encapsulated in TCP / IP, ATAoE is therefore also not routable.
- iSCSI (SCSI over IP): With iSCSI, SCSI packetsare encapsulated in TCP / IP. This results in a higher overhead, but iSCSI is routing-capable and, like Fiber Channel over IP , can also be used in wide area networks.
- HyperSCSI With HyperSCSI, SCSI packets are encapsulated in Ethernet. In contrast to iSCSI, however, there is no encapsulation in TCP / IP, which results in minor performance advantages, but HyperSCSI cannot be routed.
See also
- Fiber Channel over IP
- Internet Protocol over Fiber Channel
- Fiber Channel over Ethernet
- Linux iSCSI target with Fiber Channel support
literature
- Roland Döllinger, Reinhard Legler, Duc Thanh Bui: Practical Guide to Storage Solutions. dpunkt, Heidelberg 2010. ISBN 978-3-89864-588-1
- Björn Robbe: SAN - Storage Area Network. Hanser, Munich 2001. ISBN 978-3-446-21662-4