Bug#827322: multipath-tools: Not all paths discovered when large number of paths are present

[Ritesh Raj Sarraf]

On Wed, 2016-06-15 at 11:12 -0600, Andrew Patterson wrote:
> 
> Thanks for reminding me about max_fds. At boot:
> 
> # cat /proc/sys/fs/nr_open
> 1048576
> 
> and
> 
> # multipath -t | grep max_fds
>         max_fds "max"
> 
> So this should already be set to 1048576. I tried the test again after
> setting max_fd 1048576 in /etc/multipath.conf and got the same
> behavior.

This dates way back. 2009 is a memorable year.


https://www.redhat.com/archives/dm-devel/2009-July/msg00020.html

Quoting:

+
+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.


-- 
Ritesh Raj Sarraf | http://people.debian.org/~rrs
Debian - The Universal Operating System
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