From 4221681249dd3c2c197ec0e566845f6cb5104dda Mon Sep 17 00:00:00 2001 From: "Bryn M.Reeves" Date: Sun, 30 Aug 2009 22:36:22 +0200 Subject: [PATCH] [FAQ] document directio error when aio-max-nr is exhausted --- FAQ | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) diff --git a/FAQ b/FAQ index 35dc2f9..5ceb32b 100644 --- a/FAQ +++ b/FAQ @@ -63,3 +63,34 @@ current/default config like so: lvm dumpconfig > /etc/lvm/lvm.conf (tip from Christophe Saout) + +4. I see a lot of "io_setup failed" message using the directio checker +====================================================================== + +The directio path checker makes use of the asynchronous I/O API (aio) provided +by modern Linux systems. Asynchronous I/O allows an application to submit I/O +requests asynchronously and be notified later of their completion status. To +allow this, we must allocate an asynchronous I/O context (an object of type +aio_context_t) and this task is handled by the io_setup system call. + +A system wide limit on the number of AIO contexts that may be active +simultaneously is imposed via the aio-max-nr sysctl parameter. + +Once this limit has been reached further calls to io_setup will fail with the +error number EAGAIN leading to the "io_setup failed" messages seen for e.g. when +running "multipath -ll". + +To avoid this problem the number of available aio contexts should be increased +by setting the aio-max-nr parameter. This can be set on a one-time basis via the +/proc file system, for e.g.: + + # echo 131072 > /proc/sys/fs/aio-max-nr + +Doubles the number of available contexts from the default value of 65536. + +To make this setting persistent a line may be added to /etc/sysctl.conf: + + fs.aio-max-nr = 131072 + +Consult appropriate application and operating system tuning recommendations for +guidance on appropriate values for this parameter. -- 2.7.4