Adjusting the TCP KeepAliveTime parameter

Article:HOWTO56221  |  Created: 2011-07-25  |  Updated: 2013-09-04  |  Article URL http://www.symantec.com/docs/HOWTO56221
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Adjusting the TCP KeepAliveTime parameter

Several TCP parameters can be tuned to better accommodate typical NetBackup I/O. The I/O pattern for a Windows server is normally not a sustained data-transfer, but rather short bursts of I/O.

In certain situations, a delay may occur on a NetBackup master server before it detects that the connection to a media server has been aborted. For example, if a media server goes down during a backup, a delay may occur on the master server before it detects that the media server is no longer available. While at first there may appear to be a problem with the NetBackup master server, this delay results from a TCP/IP configuration parameter called KeepAliveTime. By default this parameter is set to 7,200,000 milliseconds (two hours). Decrease the value to 900,000 milliseconds (15 minutes).

The delay causes NetBackup jobs on the media server to appear to be active after the connection to the media server has gone down. The result is an undesirable delay before the current backup job fails and before the NetBackup retry logic starts.

A shorter timeout delay may also be needed if the I/O path includes a firewall. Firewalls are often encountered in secure networks, or when backing up the servers that are located in a DMZ or untrusted network. Firewalls typically drop the session if no traffic occurs for a set time. NetBackup does not respond well and the jobs fail. These problems usually happen during incremental backups, when the client may take a long time to send data to the media server. To solve this problem, set KeepAliveTime to a value lower than the firewall's timeout.

Table: Parameter for KeepAliveTime

Windows registry parameter (DWORD)

Recommended value

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\KeepAliveTime

0xDBBA0

(= 900,000 milliseconds, or 15 minutes)

To reduce the TCP keepalive time delay

  1. On the Windows server, click Start > Run and enter regedit.

  2. To be on the safe side, make a backup of the current registry (File > Export).

  3. Go to HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\ and create a DWORD called KeepAliveTime .

  4. Right-click on the new DWORD, select Modify, and enter 900000 (decimal) as the value.

  5. Click OK.

  6. Exit the registry editor, then turn off and restart the system.

See About tuning Windows for NetBackup.



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