iSCSI
ISCSI ( Internet Small Computer System Interface) is a method which enables the use of the SCSI protocol over TCP. As in the conventional, there is a SCSI controller (initiator) that controls the communication. The storage devices (hard drives, tape drives, optical drives, etc. ) are called target.
3260/UDP
Features and Functions
The specification of the iSCSI standard was created by the Storage Networking Industry Association and held in RFC 3720 by the Internet Engineering Task Force.
ISCSI specifies the transmission and the operation of direct memory native protocols over TCP. In this method SCSI data into TCP / IP packets are encapsulated and transported over IP networks (ports 860, 3260 ). When multipath iSCSI routing the SCSI commands are first passed to a SCSI router, the cost and based on existing mapping tables and parameters such as network load determines the preferred address of the corresponding target system (target) and to communicate with the SCSI data source selects. After this selection, the packets are encapsulated in TCP / IP and forwarded to the network adapter, which then sends the packets over the network.
ISCSI is used to allow a virtual point-to -point connection to the access to the storage area network without separate storage units have to be placed. Existing network components (Switch) can be used, since no special hardware for the new node connections is necessary, as for example Fibre Channel (FC) is the case. Block-based takes place on the hard disk access, so it is also suitable for databases. Access via iSCSI is also transparent, appears at the application level so as accessing a local hard drive.
Advantages and disadvantages compared to Fibre Channel
To implement iSCSI is almost exclusively used Ethernet. The same advantages and disadvantages of this approach is the encapsulation of data packets in Ethernet and TCP / IP. Advantage of the Ethernet base is that recourse to already widespread network standards, and in the same storage network technology and components (cabling, switches, etc. ) used to come as in the rest of the network. Another advantage afforded by TCP / IP, the routing capability and suitability for complex, enterprise-wide network structures as well as for wide area networks. The disadvantage about 10 to 20% lower efficiency, which by the additional Ethernet and TCP / IP protocol requirements (additional overhead) and constraints ( such as packet sizes) is comes about that in an increased CPU load as well as to higher I / O requirements may result (more interrupts per data set) for the server - and also provides higher latencies. Ethernet does not offer affordable daisy chained Arbitrated Loop (FC- AL) topology on different Ethernet switches clear of FC switches ( or FC directors), which, for example, as a Switched Fabric (FC -SW) additional high-availability functionality offer. Particularly disadvantageous for use in the storage network but may also be unsuitable Ethernet switches that run in Store-and- forward mode and therefore cause significantly higher latencies as FC switches. But there are already hardware solutions such as network cards with TCP / IP Offload Engine, iSCSI offload engine or the I / OAT help to minimize at least the TCP / IP overhead problem of additional CPU load. There are also optimized switches that provide very low latency time. The speed of iSCSI, just like the Fibre Channel (FC) is limited by the speed of network technology used. When using an Ethernet network to a 1 Gb / s iSCSI is thus significantly slower than FC with its usual today 2, 4 or 8 Gbit / s With 10 Gigabit / s Ethernet and thus achievable throughputs then provides iSCSI but again a higher speed in comparison - at about comparable latencies. This results in the current approach, which speaks of converged networks.
FC packets have a more favorable ratio between overhead and payload (user data ) as standard iSCSI, but are available for iSCSI jumbo frames available that (special network components provided ) may offer a more favorable ratio. The payload of an FC frame is up to 2112 bytes of protocol overhead is only 36 bytes. The TCP / IP -based iSCSI without jumbo frames has the following ratio: 1460 Bytes/76 bytes; with 9000 byte Jumbo frames: 8960 bytes Bytes/76.
Converged 10GbE
Converged 10GbE is a standard for networks in which 10 GbE and 10 GbFC are fused. For Converged approach, the new FCoE heard (Fibre Channel over Ethernet). This FC packets are encapsulated in Ethernet and then also used the Converged Ethernet topology for this - for example, according to updated switches ( packet sizes ) are then transparent for FC and iSCSI storage as well as for the LAN usable.
Implementations
Similar standards
- ATA over Ethernet: For ATA over Ethernet ATA / ATAPI packets are encapsulated in Ethernet. In contrast to iSCSI but there is no encapsulation in TCP / IP, this gave rise to slight performance benefits, but ATAoE is not routable.
- Fibre Channel: FC defines a non- routable protocol standard in the field of storage networks, designed as the successor to SCSI for high-speed transmission of large amounts of data. FC is not compatible with the Ethernet, it is a separate infrastructure (NICs, switches, etc. ) is required.
- Fibre Channel over Ethernet: For Fibre Channel over Ethernet Fibre Channel packets are encapsulated in Ethernet. In contrast to iSCSI but there is no encapsulation in TCP / IP, this gave rise to low performance advantages, but FCoE is not routable.
- Fibre Channel over IP: Fibre Channel over IP Fibre Channel packets are encapsulated in TCP / IP. FCoIP is therefore routable.
- HyperSCSI: In HyperSCSI SCSI packets are encapsulated in Ethernet. In contrast to iSCSI but there is no encapsulation in TCP / IP, this gave rise to slight performance benefits, but HyperSCSI is not routable.