[ovirt-users] iSCSI and multipath

[Nicolas Ecarnot]

Hi,

Context here :
- 2 setups (2 datacenters) in oVirt 3.4.1 with CentOS 6.4 and 6.5 hosts
- connected to some LUNs in iSCSI on a dedicated physical network

Every host has two interfaces used for management and end-user LAN 
activity. Every host also have 4 additional NICs dedicated to the iSCSI 
network.

Those 4 NICs were setup from the oVirt web GUI in a bonding with a 
unique IP address and connected to the SAN.

Everything is working fine. I just had to manually tweak some points 
(MTU, other small things) but it is working.


Recently, our SAN dealer told us that using bonding in an iSCSI context 
was terrible, and the recommendation is to use multipathing.
My previous experience pre-oVirt was to agree with that. Long story 
short is just that when setting up the host from oVirt, it was so 
convenient to click and setup bonding, and observe it working that I did 
not pay further attention. (and we seem to have no bottleneck yet).

Anyway, I dedicated a host to experiment, I things are not clear to me.
I know how to setup NICs, iSCSI and multipath to present the host OS a 
partition or a logical volume, using multipathing instead of bonding.

But in this precise case, what is disturbing me is that many layers 
described above are managed by oVirt (mount/unmount of LV, creation of 
bridges on top of bonded interfaces, managing the WWID amongst the cluster).

And I see nothing related to multipath at the NICs level.
Though I can setup everything fine in the host, this setup does not 
match what oVirt is expecting : oVirt is expecting a bridge named as the 
iSCSI network, and able to connect to the SAN.
My multipathing is offering the access to the partition of the LUNs, it 
is not the same.

I saw that multipathing is talked here :
http://www.ovirt.org/Feature/iSCSI-Multipath

I here read :
>     Add an iSCSI Storage to the Data Center
>     Make sure the Data Center contains networks.
>     Go to the Data Center main tab and choose the specific Data Center
>     At the sub tab choose "iSCSI Bond"

The only tabs I see are "Storage/Logical Networks/Network 
QoS/Clusters/Permissions".

In this datacenter, I have one iSCSI master storage domain, two iSCSI 
storage domains and one NFS export domain.

What did I miss?

>     Press the "new" button to add a new iSCSI Bond
>     Configure the networks you want to add to the new iSCSI Bond.

Anyway, I'm not sure to understand the point of this wiki page and this 
implementation : it looks like a much higher level of multipathing over 
virtual networks, and not at all what I'm talking about above...?

Well as you see, I need enlightenments.

-- 
Nicolas Ecarnot