[dm-devel] Custom priority callout

[Jim Lester]

Compellent SANs can do a mix of both Fibre connections and iSCSI
connections to the same volume. So some of our customers are looking for
ways to do more complex set ups with iSCSI as a failover situation
behind multiple fibre connections. 

Multibus works fine if they are using like connections, but if not, we
wanted to be able to make sure that the faster connections come up on
top. 

---
Jim Lester

-----Original Message-----
From: dm-devel-bounces at redhat.com [mailto:dm-devel-bounces at redhat.com]
On Behalf Of Konrad Rzeszutek
Sent: Wednesday, August 13, 2008 9:52 AM
To: device-mapper development
Subject: Re: [dm-devel] Custom priority callout

On Wed, Aug 13, 2008 at 09:32:27AM -0500, Jim Lester wrote:
> I know that the issue with writing custom priority callouts is that
they
> need to be running in RAM so that if the disk is lost, it can be
called
> again. 
> 
> My question is, if I write a custom binary file, and statically
compile
> it so it doesn't link against any libraries, does multipath
> automatically load it into RAM because it mentioned in the config
file,
> or is their other code that has to be modified to load it. 

It will most certainly be evicted from memory. You might be better of
using
the more recent versions of multipath and making your custom priority
callout
as one of the libraries in the 'libprio' directory. You will need to
modify the Makefile
and the libprio.c to include your code. Keep in mind if you segfault in
it
you will bring down multipathd with it.

Oh, and do post it on this mailing list so that multipath can nativly
support
the Compellant path priority code (I thought it was multibus??)

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