Adapter performance guidelines

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TheAIX® operating system provides a number of guidelines to maximize adapter performance.

User payload data rates can be obtained by sockets-based programs for applications that are streaming data over a TCP connection. For example, one program send( ) calls and the receiver recv( ) calls. The rates are a function of the network bit rate, Media Transmission Unit (MTU) size (frame size), physical level overhead such as the inter-frame gap and preamble bits, DataLink headers, and TCP/IP headers and a Gigahertz speed processor. These rates are best case numbers for a single LAN, and can be lower if going through routers or additional network hops or remote links.

Single direction (simplex) TCP streaming rates are rates that can be seen by a workload like FTP sending data from system A to system B in a memory-to-memory test. See the ftp command. Full duplex media functions better than half duplex media because the TCP acknowledgements can flow back without contending for the same wire that the data packets are flowing on.

Note: In the following tables, the Raw bit Rate value is the physical media bit rate and does not reflect physical media overheads such as Inter-Frame gaps, preamble bits, cell overhead (for ATM), DataLink headers and trailers. These values reduce the effective usable bit rate of the wire.
The following table lists maximum network payload speeds and the single direction (simplex) TCP streaming rates:
Table 1. Maximum network payload speeds versus simplex TCP streaming rates
Network type Raw bit rate (Mbits) Payload rate (Mb) Payload rate (MB)
10 Mb Ethernet, Half Duplex 10 6 0.7
10 Mb Ethernet, Full Duplex 10 (20 Mb full duplex) 9.48 1.13
100 Mb Ethernet, Half Duplex 100 62 7.3
100 Mb Ethernet, Full Duplex 100 (200 Mb full duplex) 94.8 11.3
1000 Mb Ethernet, Full Duplex, MTU 1500 1000 (2000 Mb full duplex) 948 113.0
1000 Mb Ethernet, Full Duplex, MTU 9000 1000 (2000 Mb full duplex) 989 117.9
10 Gb Ethernet, Full Duplex, MTU 1500 (with RFC1323 enabled) 10000 7200 (peak 9415)1 858 (peak 1122)1
10 Gb Ethernet, Full Duplex, MTU 9000 (with RFC1323 enabled) 10000 9631 (peak 9891)1 1148 (peak 1179)1
FDDI, MTU 4352 (default) 100 92 11.0
Asynchronous Transfer Mode (ATM) 155, MTU 1500 155 125 14.9
ATM 155, MTU 9180 (default) 155 133 15.9
ATM 622, MTU 1500 622 364 43.4
ATM 622, MTU 9180 (default) 622 534 63.6
1 The values in the table indicate rates for dedicated adapters on dedicated partitions. Performance for 10 Gigabit Ethernet adapters in virtual Ethernet Adapter (in VIOS) or Shared Ethernet Adapters (SEA) or for shared partitions (shared LPAR) is not represented in the table because performance is impacted by other variables and tuning that is outside the scope of this table.
Two direction (duplex) TCP streaming workloads have data streaming in both directions. For example, running the ftp command from system A to system B and another instance of the ftp command from system B to A concurrently is considered duplex TCP streaming. These types of workloads take advantage of full duplex media that can send and receive data concurrently. Some media, like Fibre-Distributed Data Interface (FDDI) or Ethernet in Half Duplex mode, cannot send and receive data concurrently and does not perform well when running duplex workloads. Duplex workloads do not scale to twice the rate of a simplex workload because the TCP acknowledge packets that are coming back from the receiver must compete with the data packets that are flowing in the same direction. The following table lists the two direction (duplex) TCP streaming rates:
Table 2. Maximum network payload speeds versus duplex TCP streaming rates
Network type Raw bit rate (Mbits) Payload rate (Mb) Payload rate (MB)
10 Mb Ethernet, Half Duplex 10 5.8 0.7
10 Mb Ethernet, Full Duplex 10 (20 Mb full duplex) 18 2.2
100 Mb Ethernet, Half Duplex 100 58 7.0
100 Mb Ethernet, Full Duplex 100 (200 Mb full duplex) 177 21.1
1000 Mb Ethernet, Full Duplex, MTU 1500 1000 (2000 Mb full duplex) 1811 (1667 peak) 1 215 (222 peak) 1
1000 Mb Ethernet, Full Duplex, MTU 9000 1000 (2000 Mb full duplex) 1936 (1938 peak) 1 231 (231 peak) 1
10 Gb Ethernet, Full Duplex, MTU 1500 10000 (20000 Mb full duplex) 14400 (18448 peak) 1 1716 (2200 peak) 1
10 Gb Ethernet, Full Duplex, MTU 9000 10000 (20000 Mb full duplex) 18000 (19555 peak) 1 2162 (2331 peak) 1
FDDI, MTU 4352 (default) 100 97 11.6
ATM 155, MTU 1500 155 (310 Mb full duplex) 180 21.5
ATM 155, MTU 9180 (default) 155 (310 Mb full duplex) 236 28.2
ATM 622, MTU 1500 622 (1244 Mb full duplex) 476 56.7
ATM 622, MTU 9180 (default) 622 (1244 Mb full duplex) 884 105
1 The values in the table indicate rates for dedicated adapters on dedicated partitions. Performance for 10 Gigabit Ethernet adapters in virtual Ethernet Adapter (in VIOS) or Shared Ethernet Adapters (SEA) or for shared partitions (shared LPAR) is not represented in the table because performance is impacted by other variables and tuning that is outside the scope of this table.
Note:
  1. Peak numbers represent best-case throughput with multiple TCP sessions that are running in each direction. Other rates are for single TCP sessions. The single session rates vary based on the processor frequency, specific adapter, and PCI slot type that are used.
  2. 1000 Mbit Ethernet (Gigabit Ethernet) duplex rates are for PCI-eXtended (PCI-X) adapters or peripheral component interconnect express (PCIe) adapter slots. Performance is slower on duplex workloads for PCI adapters or PCI-X adapters in PCI slots. The 10 Gb Ethernet rates that are specified are only for PCIe adapters.
  3. Data rates are for TCP/IP that uses the internet protocol version 4 (IPv4). The RFC1323 option is enabled for the following adapters:
    • Adapters with an MTU size of 4096 and larger
    • 10 Gigabit Ethernet or faster adapters
  4. Payload rate (Mb) column is in units of megabits per second, where 1 Mb is 1,000,000 bits. Payload rate (MB) column is in units of megabytes per second, where 1 MB is 1,048,576 bytes.