Custom priority callout
 

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.

Thanks.

---
Jim Lester | Linux Product Specialist
Jim.Lester@Compellent.com
(o) 952.294.2802
(c) 763.218.6012
Compellent Technologies | www.compellent.com


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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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Custom priority callout
 

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@redhat.com [mailto:dm-devel-bounces@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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Custom priority callout
 

On Wed, Aug 13, 2008 at 09:57:22AM -0500, Jim Lester wrote:
> 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.

Nice. I would suggest you develop a library implementation and post it
here. This way it could be integrated in all of the Linux distributions
over time and your customers won't have to download a package.

>
> 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.

I am curious how you are going to figure this out on the iSCSI connection?
Nop-out latency?

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Custom priority callout
 

By "faster" I just meant conceptually, fibre->iSCSI HBA->iSCSI software.
I didn't have any intention of actually polling the link somehow.

And I will absolutely post it back to the list once we get it written, I
already posted the hardware table definition, so that should be working
its way in here.

---
Jim Lester

-----Original Message-----
From: dm-devel-bounces@redhat.com [mailto:dm-devel-bounces@redhat.com]
On Behalf Of Konrad Rzeszutek
Sent: Wednesday, August 13, 2008 11:43 AM
To: device-mapper development
Subject: Re: [dm-devel] Custom priority callout

On Wed, Aug 13, 2008 at 09:57:22AM -0500, Jim Lester wrote:
> 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.

Nice. I would suggest you develop a library implementation and post it
here. This way it could be integrated in all of the Linux distributions
over time and your customers won't have to download a package.

>
> 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.

I am curious how you are going to figure this out on the iSCSI
connection?
Nop-out latency?

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