Bandwidth Metering in SDX
Citrix ADC SDX bandwidth metering provides you with an accurate, reliable and easy to use metering scheme that lets you to efficiently allocate processing capacity and monetize bandwidth usage in simple and accurate manner. A metering scheme is required to optimally allocate the bandwidth among various resources, keeping in mind that all the users at all the times get the allocated bandwidth.
The bandwidth allocation can be done in the following two modes:
- Dedicated bandwidth with a fixed rate of throughput
- Dedicated bandwidth with minimum assured throughput and bandwidth bursting ability
Dedicated bandwidth with a fixed rate of throughput
In this bandwidth allocation method, each VPX is assigned a dedicated bandwidth. The VPX is allowed to use the bandwidth up to the limit set. In dedicated mode the minimum and maximum bandwidth allocated are the same. If during a period of time, the VPX requires more bandwidth than allocated, then in the dedicated mode the VPX cannot increase its throughput. This can be a downside if a VPX is serving critical requests.
Also, if an SDX appliance has a number of VPXs and few of them are not utilizing their allocated bandwidth, then in dedicated mode it is not possible to share their unused bandwidth. To overcome all these challenges, a dedicated bandwidth with minimum assured rate with the ability to dynamically increase the bandwidth is useful.
Dedicated bandwidth with minimum assured throughput and bandwidth bursting ability
In this bandwidth allocation method, a VPX is allocated a minimum assured bandwidth with the flexibility to increase its bandwidth up to a preset limit. The extra bandwidth that a VPX can use is called burst capacity.
The benefit of burst capacity is that if some of VPXs are having extra capacity which they are not using, then that can be allocated to other VPX which are fully utilizing their allocated bandwidth and require more for certain periods of time. Various service providers are also interested in providing various add-on services to their customers that require dedicated capacity. At the same time they do not want to over provision bandwidth. Burstable bandwidth helps in such scenarios where the customers are assured of a specific bandwidth with the option to increase the bandwidth during high demand periods.
Selecting the Bandwidth Allocation Mode
Before you choose burstable throughput, you need to enable dynamic burst throughput allocation. To enable this option, navigate to Configuration > System and from the System Settings group, select Change System Settings. Click on the Enable Dynamic Burst Throughput Allocation check box to enable dynamic throughput.
When you provision a VPX, you can select from bandwidth burst or dynamic throughput. In the SDX UI, click Configuration > NetScaler > Instances > Add. In the Resource Allocation section of the Provision NetScaler page, choose Burstable option from the Throughput Allocation Mode drop down list for burstable throughput. If you want to use fixed rate of throughput, select Fixed. By default, fixed mode is set for bandwidth allocation. It is not necessary that all the VPXs work in the same mode. Each VPX can be configured in different mode.
Note: If you are migrating SDX from a release prior to 10.5.e, then by default all the VPXs are in the fixed allocation mode.
Determining the Maximum Burst Bandwidth for a VPX instance
The extent to which each VPX is allowed to burst is computed through an algorithm. When you provision a VPX with burstable bandwidth, then each such VPX has to be given a priority. The allocation of burstable bandwidth depends on this burst priority. The priority varies from P0 to P4 with P0 being the highest priority and P4 being the lowest.
Let us take a case where there are 2 VPX, namely VPX1 and VPX2. The minimum bandwidth allocated to VPX1 and VPX2 are 4Gbps and 2Gbps respectively with a burstable bandwidth of 2Gbps and 1Gbps each. The following table depicts the parameters:
|VPX1||Minimum assured bandwidth||4Gbps|
|Maximum Burstable bandwidth||2Gbps|
|VPX2||Minimum assured bandwidth||2Gbps|
|Maximum Burstable bandwidth||1Gbps|
In the above case, let us assume that the total licensed bandwidth is 8 Gbps. Now, if both the VPX are bursting to their maximum burstable limit, that is:
- VPX1 is using its maximum burstable bandwidth, that is 2 Gpbs then it is using a total of 4 + 2 = 6 Gbps
- VPX2 is using its maximum burstable bandwidth, that is 1 Gpbs then it is using a total of 2 + 1 = 3 Gbps
In this case the maximum bandwidth that is used is more than the licensed capacity of 8 Gbps. So to bring down the usage to within the licensed capacity, one of the VPX would have to give up its burstable bandwidth. In this case since VPX2 has lower priority than VPX1, so it gives up its 1 Gbps burstable bandwidth. VPX1 would continue to burst as it has higher priority than VPX2. In all such scenarios, it is made sure that the minimum guaranteed bandwidth is always honored.
Checking the throughput and data consumption statistics
You can check individual VPX’s throughput and data consumption statistics in graphs. These graphs are accessible from the Configuration > NetScaler > Instances page. Select a VPX and then click on the Action drop list. From the list select either Througput Statistics or Data Usage Statistics.
The graphs provide you to check the data consumption and throughput statistics for various periods of time, like:
- Last 1 hour
- Last 1 day
- Last 1 week
- Last 1 month, and
- Previous month
You can also select a specific time period in the graph by adjusting the slider at the bottom of the graph. The graph also shows the data consumption or throughput data for a specific time by moving your mouse over the lines in the graph.
The following illustration shows a sample graph of throughput data for 1 week: