I/O bandwidth

I/O bandwidth is the rate at which the CPU reads from input or writes to output through a network interface card. Therefore, network inputs and outputs affect I/O bandwidth. SDI inputs don't affect I/O bandwidth.

Impact of I/O bandwidth issues

Lack of the required input bandwidth typically results in dropped frames in the output encodes.

You might not notice output bandwidth problems in Elemental Live. Instead, the downstream systems will notice the problem.

Measuring I/O bandwidth

• To measure I/O bandwidth on an Ethernet card, use the iftop command. This command shows the bandwidth for one card over a range of time (the last 2 seconds, 10 seconds, and 40 seconds). It also shows a running total of bandwidth used since you entered the iftop command.

  Enter the iftop command. For example, to show the results for eth0, enter this command:

  [elemental@encoder ~]$ sudo iftop -t -i eth0

  To stop collecting data, press Ctrl-C.

• To measure I/O bandwidth on a Mellanox card, use the mlnx_perf command.

  Following are the expected bandwidths on the Mellanox card:

  • Workflows with SMPTE 2110 inputs or outputs, and workflows with SMPTE 2022-6 inputs require a Mellanox card. This card has a declared maximum bandwidth of 25 Gbps. In practice, the maximum bandwidth (using the latest versions of Elemental Live) is as follows:

  • For SMPTE 2110 workflows, expect approximately 24.5 Gbps per Mellanox port.

Expected bandwidth for individual workflows

The following table illustrates the difference in bandwidth that's required for two different inputs (SMPTE 2110 and SMPTE 2022-6) with two different output resolutions (HD and 4K).

Notice that the 4K output requires approximately four times as much bandwidth as the HD output.

Type of input	Resolution of the output	Expected bandwidth (Gbps) for the workflow
SMPTE 2110 (video only)	HD (1080p60)	2.6
	4Kp60	10.5
SMPTE 2022-6	1080p60	3
	4Kp60	12