MDMPD(8)							     MDMPD(8)



NAME
       mdmpd - daemon to monitor MD multipath devices


SYNOPSIS
       mdmpd


DESCRIPTION
       Enterprise  storage requirements often include the desire to have more
       than one way to talk to a single disk drive so that in  the  event  of
       some  failure  to  talk to a disk drive via one controller, the system
       can automatically switch to another controller and keep	going.	 This
       is  called  multipath disk access.  The linux kernel implements multi-
       path disk access via the software RAID stack known as the md (Multiple
       Devices)	 driver.   The kernel portion of the md multipath driver only
       handles routing I/O requests to the proper device and  handling	fail-
       ures  on the active path.  It does not try and find out if a path that
       has previously failed might be working again.  That's what this daemon
       does.   Upon  startup,  the  daemon  will fork and place itself in the
       background.  Then it reads the current state of the  md	raid  arrays,
       saves  that  state, and then waits for the kernel to tell it something
       interesting has happened.  It then wakes up,  checks  to	 see  if  any
       paths  on  a  multipath	device	have failed, and if they have then it
       starts to poll the failed path once every 15 seconds until  it  starts
       working again.  Once it starts working again, the daemon will then add
       the path back into the multipath md device it was originally  part  of
       as a new spare path.


OPTIONS
       None.  This is a very simple program that only does one thing.


FILES
   /proc/mdstat
       If you're using the /proc filesystem, /proc/mdstat lists all active md
       devices with information about them.   mdmpd  requires  this  to	 find
       arrays  to  monitor  paths  on  and to get notification of interesting
       events.




v0.3								     MDMPD(8)

UNIX/Linux commands referenced on this page:

1. talk
2. as
3. find