MDMPD(8)                                                              MDMPD(8)


       mdmpd - daemon to monitor MD multipath devices




       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 multipath
       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 failures
       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 back-
       ground.  Then it reads the current state of the md raid  arrays,  saves
       that  state,  and then waits for the kernel to tell it something inter-
       esting 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


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


       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

v0.3                                                                  MDMPD(8)

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