md and multipathing

md and multipathing

[Phy Prabab]

Hello everyone!

I have a question concerning md driver: is there a way
to have a multipath md that is mulitplexed?  That is I
have seen that when I create a multipath device, the
device only uses on channel, always seems to be the
first channel I use in the command line, to drive path
even if I do not specify the second channel as a spare
device?

I am using mdadm with 2.6.9 kernel.

mdadm --create --force -lmp -n2 /dev/md0 /dev/sda
/dev/sdc

iostat always shows data flowing across only one
channel as if the second device is in passive mode
waiting for failover.

Thank you for your time.

Phy


		
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Re: md and multipathing

[Lars Marowsky-Bree]

On 2004-10-28T17:25:02, Phy Prabab <phyprabab@yahoo.com> wrote:

> I have a question concerning md driver: is there a way
> to have a multipath md that is mulitplexed?

With 2.6, use the Device-Mapper multipath module.


Sincerely,
    Lars Marowsky-Brée <lmb@suse.de>

-- 
High Availability & Clustering
SUSE Labs, Research and Development
SUSE LINUX AG - A Novell company

Re: md and multipathing

[Phy Prabab]

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Lars et all,

This what I am doing I believe.  Here is the command:

mdadm --create --force -lmp -n2 /dev/md0 /dev/sda
/dev/sdc

First controller is /dev/sda /dev/sdb (channel a and b
respective) and the second controller is /dev/sdc
/dev/sdd (again, channel a and b respecitve).

Here I am using multipath (enabled in kernel,
268,269,2610rc1) with the two paths to the FC volume.
I have found that it only drives one channel of the md
device as reported by vmstat.  More over, the traffic
appears to only go to the first device listed e.g. if
I change the ordering and use channel "b" first, than
all traffic to the md is driven on that channel.

Put another way, this is what I believe I have done:
device 0:0:0:0 + 1:0:0:0 = md0
device 0:0:0:1 + 1:0:0:1 = md1

scsi dev sda + sdc = md0
scsi dev sdb + sdd = md1

So have I done something wrong with the setup?  Am I
to question mdadm or md device?  

I get the exact same behavior as if I were to make the
device have a sprae path i.e. mdadm --create --force
-lmp -n1 -x1 /dev/md0 /dev/sda /dev/sdc,  but without
the failover device.  What I would want is to have
traffice be "exqually balanced" across both channels
(e.g. device paths /dev/sda /dev/sdc) with hopes that
this will improve my throughput.

Thanks!
Phy
--- Lars Marowsky-Bree <lmb@suse.de> wrote:

> On 2004-10-28T17:25:02, Phy Prabab
> <phyprabab@yahoo.com> wrote:
> 
> > I have a question concerning md driver: is there a
> way
> > to have a multipath md that is mulitplexed?
> 
> With 2.6, use the Device-Mapper multipath module.
> 
> 
> Sincerely,
>     Lars Marowsky-Brée <lmb@suse.de>
> 
> -- 
> High Availability & Clustering
> SUSE Labs, Research and Development
> SUSE LINUX AG - A Novell company
> 
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