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Multipathd checks the status of every path every polling_interval seconds (usually 5). To do this, it needs an open file descriptor. Closing and re-opening these descriptors every time is not an acceptable option. Losing paths can put the system under load. Depending on which devices you lose, this can significantly delay or even make it impossible to reopen these devices. Also, keeping the multipath path devices open, keeps many programs from accidentally accessing the path devices directly, instead of accessing the multipath device. For instance, user's can't simply mount a single path of a multipath device.
It's simple to adjust the number of file descriptors with the max_fds multipath.conf variable.
multipath intentionally uses the same number of file descriptors as multipathd to make it more likely that a user will notice that they don't have max_fds set correctly. Otherwise, they might not notice it when the multipathd daemon fails. Leaving their multipath devices unable to restore lost paths.
Created attachment 513517 [details] messages Description of problem: case: testing system scalability, where host is connected via FC to 360 devices with 4 paths each, multipath is run out of fds. Jul 17 07:56:40 | out of file descriptors. set or increase max_fds in /etc/multipath.conf [root@rhev-a8c-02 ~]# lsof |grep multi |wc -l 1047 [root@rhev-a8c-02 ~]# multipath -ll | awk '/3600/' |wc -l 362 [root@rhev-a8c-02 ~]# multipath -ll | awk '/sd/' |wc -l 1448 desired: multipath should open & close fds dynamically. [root@rhev-a8c-02 ~]# ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 515767 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 3000 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 1024 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited