iSCSI
iSCSI ( internet Small Computer System Interface ) [ ˈaɪskʌzi ] is a procedure that enables the use of the SCSI protocol over TCP . As with normal SCSI, there is a controller ( initiator ) that controls communication. The storage devices (hard drives, tape drives, optical drives, etc.) are called targets .
| iSCSI | |||||||||||||||||||||||||
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| Family: | Internet protocol family | ||||||||||||||||||||||||
| Operation area: | Use of the SCSI protocol over TCP | ||||||||||||||||||||||||
| Ports: | 3260 / TCP 3260 / UDP |
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| Standards: | RFC 7143 . April 2014. (English). | ||||||||||||||||||||||||
Features and functions
The specification of the iSCSI standard was created by the Storage Networking Industry Association and recorded in RFC 3720 by the Internet Engineering Task Force . Extensions and updates were most recently combined in RFC 7143 .
iSCSI specifies the transmission and operation of direct storage protocols natively over TCP. With this procedure, SCSI data are packed in TCP / IP packets and transported over IP networks (ports 860, 3260). When multipath iSCSI routing are SCSI commands first to a SCSI router passed, the existing based on mapping tables and parameters like network load and costs the preferred address of the target system ( the target is determined and for communication with the SCSI data source) selects. After this selection, the packets are packed in TCP / IP and forwarded to the network adapter, which then sends the packets over the network.
iSCSI is used to enable access to the storage network via a virtual point-to-point connection without having to set up your own storage devices. Existing network components ( switch ) can be used, as no special new hardware is required for the node connections, as is the case e.g. B. is the case with Fiber Channel (FC). Access to the hard drives is block-based , so it is also suitable for databases. Access via iSCSI is also transparent, so it appears at the application level as access to a local hard drive.
Advantages and disadvantages compared to Fiber Channel
Ethernet is used almost exclusively to implement iSCSI. The advantage and disadvantage of this approach is the encapsulation of data packets in Ethernet and TCP / IP . The advantage of the Ethernet base is that already widespread network standards are used and the same technology and components (cabling, switches, etc.) are used in the storage network as in the rest of the network. Another advantage of TCP / IP is the routing capability and suitability for complex, company-wide network structures as well as for wide area networks. The disadvantage is the somewhat poorer efficiency that results from the additional Ethernet and TCP / IP protocol requirements (additional overhead) and restrictions (such as packet sizes) and leads to increased CPU load and higher I / O requirements ( more interrupts per data volume) and can lead to higher latencies. Ethernet also does not offer a low-cost Daisy-Chained Arbitrated Loop (FC-AL) topology. Unsuitable Ethernet switches can also be disadvantageous for use in storage networks, which offer too little buffer memory for short-term compensation of excessive data volumes or which cause higher latencies than FC switches due to store and forward and unsuitable internal structure. But there are already hardware solutions such as B. network cards with TCP / IP offload engine , iSCSI offload engine or I / OAT are available, which at least minimize the TCP / IP overhead problem of the additional CPU load. There are also optimized switches that offer particularly low latency times. The speed of iSCSI, just like that of Fiber Channel (FC), is limited by the speed of the network technology used. When using an Ethernet network with individual 1 Gbit / s links, iSCSI is therefore significantly slower than FC with its 2, 4 or 8 Gbit / s, which is common today. With 10 Gigabit / s Ethernet and the throughputs that can be achieved with it, iSCSI then again offers a comparatively higher speed - with approximately comparable latencies. This results in the approach of converged networks.
- Package structure / payload
FC packets have a more favorable ratio between overhead and payload (user data) than iSCSI over standard Ethernet, but with suitable network components, jumbo frames can also be used with iSCSI , which can offer a more favorable ratio. The payload of an FC frame is up to 2048 bytes, the protocol overhead is only 36 bytes for the frame header and 24 bytes for the interframe gap . The TCP / IP-based iSCSI without jumbo frames has the following ratio: 1460 byte payload with 78 byte overhead; Jumbo frames with 9000 bytes MTU : 8960 bytes payload at 78 bytes. The 48-byte iSCSI headers are only transmitted at the beginning of a transaction of up to 16 MiB and are practically insignificant.
- Comparison by speeds
| Surname | Nominal speed ( GBit / s ) | Data throughput (in each direction in MByte / s) | Efficiency | Publishing year |
|---|---|---|---|---|
| Fiber Channel 1GFC | 1.0625 ( 8b10b -coded) | 103 | 97.2% | 1997 |
| iSCSI over Gigabit Ethernet | 1,000 | 119 | 94.9% ( MTU 1500) | 2004 |
| Fiber Channel 2GFC | 2.125 (8b10b) | 206 | 97.2% | 2001 |
| Fiber Channel 4GFC | 4.25 (8b10b) | 413 | 97.2% | 2005 |
| Fiber Channel 8GFC | 8.5 (8b10b) | 826 | 97.2% | 2008 |
| Fiber Channel 10GFC | 10.52 ( 64b66b -coded) | 1239 | 97.2% | 2004 |
| Fiber Channel over 10G Ethernet 10GFCoE | 10 | 1206 | 96.5% ( MTU 2500) | 2009 |
| iSCSI over 10G Ethernet | 10 | 1239 | 99.1% ( MTU 9000) | 2004 |
| Fiber Channel 20GFC | 21.04 (64b66b) | 2478 | 97.2% | 2008 |
Converged 10 GbE
Converged 10 GbE is a standard for networks where 10 GbE and 10 GbFC are merged. The converged approach also includes the new FCoE ( Fiber Channel over Ethernet ). FC packets are encapsulated in Ethernet and the converged Ethernet topology is also used for these - e.g. B. then appropriately updated switches (packet sizes) can be used transparently for FC and iSCSI storage as well as for the LAN.
Implementations
| operating system | Publication date | version | Techniques supported |
|---|---|---|---|
| i5 / OS | October 2006 | i5 / OS V5R4M0 | Target, multipath |
| VMware ESX | June 2006 | ESX 3.0.0, ESX 3.5, ESX 4 | Initiator, multipath |
| AIX | October 2002 | AIX 5.2, AIX 5.3, AIX 6.1 | Initiator, Target (AIX 5.3 and higher only), Multipath IBM iSCSI software initiator and software target on AIX 6.1 |
| Windows | June 2003 | 2000, XP Pro, 2003, Vista, 2008, 7, 8, 2012 | Initiator, target (only in Windows Storage Server, Windows Server 2008 R2, Windows Server 2012), multipath |
| NetWare | August 2003 | NetWare 5.1, 6.5, & OES | Initiator, target |
| HP-UX | October 2003 | HP 11i v1, HP 11i v2 | initiator |
| Solaris | February 2005 | Solaris 10, 11 | Initiator, target, multipath |
| Linux | June 2005 | 2.6.12, from 2.6.38 LIO | Initiator, target (FCAL, FCoE), multipath |
| NetBSD | February 2006 | 4.0, 5.0 | Initiator (5.0), Target (4.0), Multipath |
| OpenBSD | May 2011 | from version 4.9 | initiator |
| FreeBSD | February 2008 | 7.0 | Initiator, target, multipath |
| OpenVMS | February 2008 | 8.3-1H1 | Initiator, multipath |
| Mac OS X | July 2008 | 10.4-10.5 | Initiator , target |
Similar standards
- ATA over Ethernet : With ATA over Ethernet, ATA / ATAPI packets are encapsulated in Ethernet. In contrast to iSCSI, there is no encapsulation in TCP / IP, which results in minor performance benefits, ATAoE is not routable.
- Fiber Channel : FC defines a non-routable standard protocol from the field of storage networks, which was designed as a successor to parallel SCSI for the high-speed transmission of large amounts of data. Native FC is not compatible with Ethernet, a separate infrastructure (NICs, switches, etc.) is required.
- Fiber Channel over Ethernet : With Fiber Channel over Ethernet, Fiber Channel packets are encapsulated in Ethernet. In contrast to iSCSI, there is no encapsulation in TCP / IP, which results in minor performance advantages, but FCoE cannot be routed.
- Fiber Channel over IP : With Fiber Channel over IP, Fiber Channel packets are also encapsulated in TCP / IP. FCoIP is therefore routable.
- HyperSCSI : With HyperSCSI, SCSI packetsare encapsulated in Ethernet. In contrast to iSCSI, there is no encapsulation in TCP / IP, which results in minor performance advantages, HyperSCSI cannot be routed.
Web links
- LIO - Linux iSCSI target and initiator - upstream from 2.6.38
- IBM dares to launch a new iSCSI on heise online from August 29, 2007
- iSCSI Client and Server Implementation Linux-iSCSI (Open Source, English)
- iSCSI Client Open-iSCSI (Open Source, English)
- iSCSI Target (iSCSI Software Server for Linux, English)
- RisingTide Systems iSCSI target and initiator for Linux based on LIO
- iSCSI / Internet SCSI - IP-SAN read values via iSCSI
- ISCSI basics
- Microsoft iSCSI Software Target 3.3 for Windows Server 2008 R2 (English)
Individual evidence
- ↑ iSCSI over Ethernet with 1500 byte standard MTU : 94.9%; iSCSI with 9000 byte MTU jumbo frames : 99.1%; Fiber Channel: 98.3% - without taking Layer 1 coding into account
- ↑ a b Ujjwal Rajbhandari: Comparing Performance Between iSCSI, FCoE, and FC. (No longer available online.) In: Enterprise Technology Center. Dell October 2009, archived from the original on August 20, 2010 ; accessed on October 20, 2010 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ a b c d e f g Mario Vosschmidt: Storage Trends 2010. (PDF; 2.2 MB) LSI Logic GmbH, 2010, accessed on October 20, 2010 .
- ↑ a b RFC 7143 . - Internet Small Computer System Interface (iSCSI) Protocol (Consolidated) . April 2014. (Replaces RFC 5048 - English).
- ↑ Solaris 11 Documentation: COMSTAR Replaces iSCSI Target Daemon , accessed February 5, 2013.
