Archiving performance through load balancer significantly slower than expected.

Problem

Archiving rates are slower than expected while network traffic is going through a load balancer. Higher than expected network latency is being observed communicating between the Enterprise Vault servers and it's archiving targets.

Error Message

No error message may be seen however a much larger latency on network request response times for smaller HTTP or TCP Packets will be observed versus direct network traffic to the target servers from Enterprise Vault. 

Cause

It has been seen that the default settings of some load balancers introduce negative effects in terms of network latency communicating between Enterprise Vault and target servers. This can occur because by default some load balancers are configured to use Nagle's Algorithm. The setting, Nagle's Algorithm has unintended effects when requests and responses require small HTTP or TCP based packets. As the below states, when Nagle's Algorithm is enabled, data will be stacked and made to wait until all data is acknowledged on a connection before sending more data. This stacking of data causes a negative impact on Enterprise Vault archiving as small packets of data are transferred continually during the archiving process. 





Note:  Nagle's Algorithm has an even more pronounced impact on Exchange 2013/2016 archiving/journaling as compared to Exchange 2010/2007/2003. This is due to the fact that exchange 2013/2016 uses RPC/HTTP as it's default protocol for Outlook clients. In previous exchange versions, the default protocol to connect to exchange was RPC/TCP (MAPI). HTTP packets are much smaller than TCP based packets. The smaller the packets are the more delays will be experienced as a result of Nagle's Algorithm being enabled. 

Solution

As a workaround, it may be possible to use hosts file entries to bypass the load balancer to confirm archival performance improves while bypassing the load balancer. The hosts file entry should point to the CAS server IP address Outlook is using to connect.  

Example:

CAS_IP_ADDRESS   MAIL.EV.LOCAL 

Note: In some environments, it may not be possible to bypass the load balancer to access the target servers directly. 






The recommendation is to disable Nagle's Algorithm.