[dm-devel] multipath-tools : A way needless to restart multipathd damon while attaching new device to host which met a path failure

[Benjamin Marzinski]

While having multipathd retain failed devices when it restarts may be a
little tricky, since it won't know anything about those devices, having
it retain these devices during a reload (which is enough to be able to
change the configuration) should be doable.  I agree that multipathd
should not be removing devices if they haven't been removed from the
system since, like you say, that will keep multipathd from reacting to
the device's later recovery.

I'll take a look into doing this.

-Ben

On Mon, May 23, 2016 at 03:38:35AM +0000, Gechangwei wrote:
>    Hi,
> 
>     
> 
>    I encountered an  issue that  devmapper disappeared  while the  multipathd
>    dameon was restarted.
> 
>     
> 
>    Digging into  the root  cause of  preceding issue,  I found  storage  path
>    failure while  restarting the  multipathd daemon.  It seems  unreasonable,
>    because the storage path may recover in the future.
> 
>     
> 
>    When  using  multipath-tools  to   create  device  mapper,  I   configured
>    “blacklist section”  and “blacklist  exception  section”, which  meets  my
>    requirement that only a small part of  SCSI disk can be used underneath  a
>    device mapper.
> 
>     
> 
>    After restarting the multipathd daemon, the device mapper of path  failure
>    disappears and it won’t  comeback even the storage  paths recover. So  the
>    file system on that devmapper can’t be available.
> 
>     
> 
>    I wonder that if there is a solution that a device mapper of path  failure
>    can come back to active even I restart the multipathd daemon?
> 
>     
> 
>    If such a solution exists, it will be marvelous
> 
>     
> 
>    If not,  I  propose  a  userland  interface  to  add  blacklist  exception
>    dynamically. After the blacklist exception is added to “conf”, “multipathd
>    add map $map” and  “multipathd add path”  can be used to  add new map  and
>    path.
> 
>     
> 
>    In a nutshell, we can dynamically  add elist, map and paths  respectively.
>    And multipathd  damon  is  not  necessary  to  restart  due  to  preceding
>    solution.
> 
>     
> 
>    Any experts of DM have any comments  on my solution and the issue I  faced
>    with?
> 
>     
> 
>     
> 
>    Your reply is very important to me.
> 
>     
> 
>    Thanks.
> 
>     
> 
>    BR.
> 
>     
> 
>    Chauncey Ge
> 
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