BIO_RW_FAILFAST

I have been having problems with systems getting I/O errors and dropping mounted filesystems, when it is processing a RCSN caused by some other event on the fabric within its' zone. If I unset BIO_RW_FAILFAST in dm-mpath.c I no longer get the I/O errors and of course no filesystem drops. Are there any plans to change this, or make it a settable option? Are there any negatives to not setting it?

Andy

What is "RCSN"? What hardware? And why does it show up on all paths at once?

Sincerely,
Lars Marowsky-Brée <[email protected]>

High Availability & Clustering
SUSE Labs, Research and Development
SUSE LINUX Products GmbH - A Novell Business	 -- Charles Darwin
"Ignorance more frequently begets confidence than does knowledge"

He must have meant a RSCN: Registered State Change Notification ...

Likely qlogic or emulex hardware. AFAIUI, the fibre switch sends an RSCN to all initiators when it sees a change on the fabric, for example detaching a cable from the switch or target.

AFAIR some RSCN's can cause glitches, and the FC driver generally wants scsi core (or here, with fail fast set, maybe dm multipath) to just resend the command.

I recall some recent changes to qlogic for retry handling in this area, maybe as part of the queue removal code.

Seems likely that the fast fail is hurting if we get a DID_BUS_BUSY or ??? from the driver.

Seeing the actual IO errors and kernel versions might help, cc-ing linux-scsi.

Maybe Andrew Vasquez (or James Smart) can comment.

-- Patrick Mansfield