mdmpd - Unix, Linux Command
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. Thats
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.
None. This is a very simple program that only does one thing.
If youre using the
/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.