Section F: Tuning a streaming media cache for performance

About tuning and load balancing

This section contains information regarding tuning by load balancing when you are operating your NetCache appliance as a streaming media cache with a WCCP 2.0 router or an L4 switch.

It also provides instructions on gathering streaming media data and interpreting the statistics to gauge the performance of a streaming media cache.

Importance of load balancing data over network interfaces

You cannot achieve optimal performance unless you first ensure that your network deployment properly load balances connections across the network interfaces of your NetCache appliance.

Streaming media proxies can deliver streaming data to clients very quickly over multiple network interfaces. However, if a proxy is forced to deliver streaming data only over a single interface, the proxy is likely to become limited in its network throughput by the bandwidth of the single network interface.

To ensure proper load balancing, do both of the following:

To load balance client connections, deploy the streaming media proxy with a router running WCCP 2.0 and configure the WCCP NetCache IP Addresses for Load Balancing option on the Transparency - WCCP Global Settings page under the Setup tab of the Appliance Manager.
To load balance server connections, configure the Load Balancing Interfaces option on the Network - General Settings page under the Setup tab of the Appliance Manager.
Note
Network Appliance recommends that you configure both the WCCP NetCache IP Addresses for Load Balancing option and the Load Balancing Interfaces option.

Load balancing with WCCP 2.0

When you deploy your NetCache appliance with a router running WCCP, you can enable NetCache to deliver data over multiple network interfaces by setting the WCCP Load Balancing option on the Transparency Settings page; you list the NetCache network interfaces over which you want NetCache to deliver data to clients. If you do not list any network interfaces, NetCache delivers data to clients over a single interface, which NetCache chooses.

Use the following guidelines to determine which, if any, network interfaces to list in the WCCP Load Balancing option:

List only IP addresses for network interfaces through which this NetCache appliance communicates with clients. Do not, for example, list a network interface through which the NetCache appliance communicates with another NetCache appliance.
When using server-side load balancing and WCCP load balancing, make sure that the WCCP load balancing list is consistent with the server-side load balancing list if the NetCache appliance uses the WCCP router as a default gateway to servers. If the lists are not consistent, requests initiated by the appliance using an IP address that is not in the WCCP load balancing list might be returned to the appliance in a routing loop.
Typically, NetCache can deliver HTTP and NNTP data over a single network interface without adversely affecting performance.

Load balancing using the Load Balancing Interfaces option

By listing the IP addresses of all the network interfaces of your NetCache appliance in the Load Balancing Interfaces option on the Network - General Settings page, you enable NetCache to send out requests with different source IP addresses. This configuration ensures that Web and streaming server requests and responses are distributed over multiple network interfaces.

Note
Configuring the Load Balancing Interfaces option is beneficial if you expect the NetCache appliance to handle a large number of on-demand streaming requests.

Load distribution using a Foundry ServerIron L4 switch

If you are using a Foundry ServerIron L4 switch, you must configure the switch to ensure an even distribution of client connections across the cache interfaces by using round-robin or hashing on the client (source) IP address.

Check your firewall configuration

Ensuring that the NetCache appliance interacts correctly with the firewall is of paramount importance in establishing and maintaining streaming media quality. You can avoid many streaming media problems by ensuring that you have properly set up access to the firewall and have opened the required ports for streaming media.

The following list describes the effectiveness of each transport:

UDP
UDP is the recommended transport for steaming media, and streaming media quality is highest when UDP is allowed. However, all UDP streaming connections require additional TCP control connections. Therefore, to implement UDP streaming, you must also open the streaming TCP ports on the firewall.
TCP
The quality of your streaming media degrades when TCP is used for data transport. However, you do not have to open UDP ports to enable TCP streaming. (QuickTime streaming requires UDP ports.)
HTTP encapsulation
Streaming media quality is poorest when HTTP encapsulation is used for data transport. NetCache supports both server-side HTTP encapsulation and client-side HTTP encapsulation.
HTTP proxied
If you do not have a streaming license or streaming is disabled, NetCache will proxy streaming traffic over HTTP (TCP port 80). When NetCache proxies streaming requests over HTTP, NetCache does not split or cache the traffic. From a bandwidth perspective, HTTP proxying is the least desirable method of transporting streaming media.

Note
See the Command Line Reference for category descriptions, syntax, and examples of CLI commands.

Using streaming media statistics to gauge performance

The Streaming - General Statistics page and the Streaming - Detailed Statistics page under the Data tab in the Appliance Manager provide traffic statistics about streaming real-time information, and streaming media connections and performance. You can customize the statistics reported in the Statistics tab page by selecting or clearing fields in the Options tab.

The following table shows some of the performance problems indicated by the statistics on the Streaming Media Instrumentation page.

If this is the case...	Then...
The General Statistics page shows a large number of delayed connections.	The NetCache appliance is heavily loaded and you should take immediate action to decrease its load.
The Bytes Queued statistics show a large number of queued bytes.	A network problem exists. Check the client statistics to determine whether this problem is client-related. If the problem is not client-related, use `sysstat` to check if CPU capacity is at 100 percent or if network interfaces are at maximum throughput. Verify that data is properly load-balanced across all network interfaces.
The Packets Delayed statistics show that clients are dropping bytes.	The network or client is experiencing problems. Check the Client Bytes Received statistics and Client Bytes Sent statistics to see if a particular client, or group of clients, is dropping bytes.
The client information statistics indicate that more than 5 percent of clients are dropping packets.	A network or client problem exists. Check the Streaming access log to see if a particular client, or group of clients, is affected. To see streaming statistics, use the `sysstat -S` command.

CLI commands you can use to gather streaming data

The following CLI commands can be used to gather data about the performance of the streaming media cache:

sysstat
Provides statistics indicating the current CPU usage, and the amounts of network and disk I/O.
sysstat -p
Provides statistics about packets.
sysstat -S
Provides streaming statistics indicating the current system load.
show status.streaming.*
Provides statistics for streaming connections. These statistics are identical to those provided in the Appliance Manager.
netstat -an
Displays the current network conditions.
netstat -p tcp
Displays the current TCP statistics. The cache must be rebooted to clear TCP statistics.
ifstat -a
Provides statistics about the interfaces enabled on the NetCache appliance.
smstats
Provides statistics for active streaming connections.