<div dir="ltr">Hello, This is related to an issue raised by Richard Sharpe recently. <a href="https://www.redhat.com/archives/dm-devel/2015-August/msg00154.html">https://www.redhat.com/archives/dm-devel/2015-August/msg00154.html</a> The RPM that was used- <a href="http://vault.centos.org/6.6/updates/Source/SPackages/device-mapper-multipath-0.4.9-80.el6_6.3.src.rpm">http://vault.centos.org/6.6/updates/Source/SPackages/device-mapper-multipath-0.4.9-80.el6_6.3.src.rpm</a> Problem: From reading the source code, I understand that 2 APIs defined in libmpathpersist/mpath_persist.c do a system-wide scan of all SCSI devices by sending asynchronous IO (io_submit calls) to test if SCSI device path is good: extern int mpath_persistent_reserve_in (int fd, int rq_servact, struct prin_resp *resp, int noisy, int verbose); extern int mpath_persistent_reserve_out ( int fd, int rq_servact, int rq_scope, unsigned int rq_type, struct prout_param_descriptor *paramp, int noisy, int verbose); So, to get a persistent reservation on a single /dev/mapper/mpathx device on a system having 400 SCSI devices, current code does 400 reads of 4K each.(512 bytes of 8 sectors), leading to huge delays. Root cause of the system wide device scan: The system-wide scan is triggered by setting the DI_CHECKER bit in the flags argument to a path_discovery() API: if (path_discovery(pathvec, conf, DI_SYSFS | DI_CHECKER)) { ret = MPATH_PR_DMMP_ERROR; goto out1; } /* get info of all paths from the dm device */ if (get_mpvec (curmp, pathvec, alias)){ condlog(0, "%s: failed to get device info.", alias); ret = MPATH_PR_DMMP_ERROR; goto out1; } I believe the DI_CHECKER bit in path_discovery() API is not needed. This is because the path status checking is already done on the specific mpath device in the get_mpvec API. The get_mpvec() gets the required struct multipath *mpp, and then invokes pathinfo(pp, conf->hwtable, DI_CHECKER) for each path in the multipath dev. And this checks state of each path for the multipath device. if (mask & DI_CHECKER) { pp->chkrstate = pp->state = get_state(pp, 0); Possible solution: I have a patch ready that simply removes the DI_CHECKER bit from the path_discovery() calls inside mpath_persistent_reserve_in() and mpath_persistent_reserve_out(). Attached the patch. I have tested out the following PRIN and PROUT commands and don't see any errors. mpathpersist -i -k /dev/mapper/mpathig mpathpersist -i -r /dev/mapper/mpathig mpathpersist --out --register --param-rk=0A041D3d /dev/mapper/mpathig mpathpersist --out --register --param-sark=0A041D3d /dev/mapper/mpathig mpathpersist --out --reserve --param-rk=0A041D3D --prout-type=5 --verbose=3 /dev/mapper/mpathig Request someone to review the patch, suggest changes and guide me in fixing this issue. Thanks, Satyajit</div>