Lustre 1.6 Operations Manual

20.1.3.1 Configuring Adaptive Timeouts
One of the goals of adaptive timeouts is to relieve users from having to tune the
obd_timeout value. In general, obd_timeout should no longer need to be
changed. However, there are several parameters related to adaptive timeouts that
users can set. Keep in mind that in most situations, the default values will be usable.
The following parameters can be set as module parameters in modprobe.conf or at
runtime in /sys/module/ptlrpc. 1
Note – This directory path may be different on some systems.
Parameter
Description
at_min Sets the minimum adaptive timeout (in seconds). Default value is 0.
The at_min parameter is the minimum processing time that a server
will report. Clients base their timeouts on this value, but they do not
use this value directly. If you experience cases in which, for unknown
reasons, the adaptive timeout value is too short and clients time out
their RPCs, then you can increase the at_min value to compensate
for this. Ideally, users should leave at_min set to its default.
at_max
Sets the maximum adaptive timeout (in seconds). In Lustre 1.6.5, the
default value is 0 * . This setting causes adaptive timeouts to be
disabled and the old fixed-timeout method (obd_timeout) to be
used. The at_max parameter is an upper-limit on the service time
estimate, and is used as a ‘failsafe’ in case of rogue/bad/buggy code
that would lead to never-ending estimate increases. If at_max is
reached, an RPC request is considered ‘broken’ and it should time
out.
NOTE: It is possible that slow hardware might validly cause the
service estimate to increase beyond the default value of at_max. In
this case, you should increase at_max to the maximum time you are
willing to wait for an RPC completion.
at_history
Sets a time period (in seconds) within which adaptive timeouts
remember the slowest event that occurred. Default value is 600.
1. The specific sub-directory in ptlrpc containing the parameters is system dependent.
20-6 Lustre 1.6 Operations Manual • September 2008