[dm-devel] device mapper / multipath

[Malahal Naineni]

Tarak Reddy [tarak.reddy at in.ibm.com] wrote:
>    Hello,
>    I am facing one issue on LVM & Multipath setup on scsi devices. This test was running with blast and blast got hung after couple hours run. At this particular time multipath -ll show as all paths are faulty even though lsscsi command able to show attached devices and corresponding HBA was online. This test was running with scsi_logging_level=6 and multipath is not able to updates his paths as it complains "test unit ready" command is not working on any of those paths.

"lsscsi" command doesn't send any I/O to make sure that they are
operational. Please do "dd if=/dev/sdX of=/dev/null count=1
iflag=direct" to make sure they are operational.

>    I have collected the dump and I/O got blocked for device mapper devices not for underlying scsi devices( as device mapper could able get which path it can use from path selector in dm-multipath). Below has some debug logs.

>    What is device-mapper-multipth behavior on IO request already placed in queue and going to be queued when no path is available or path went off? In my case as paths were not available in b/w and I/O seems to blocked which made application(blast) to be hung.

The behavior depends on your multipath configuration (queue_if_no_path
etc), but looks like your paths are all dead in your case though.

Regards, Malahal.