[ovirt-users] iSCSI and multipath

[Nicolas Ecarnot]

Le 09-06-2014 13:55, Maor Lipchuk a écrit :
> Hi Nicolas,
> 
> Which DC level are you using?
> iSCSI multipath should be supported only from DC with compatibility
> version of 3.4

Hi Maor,

Oops you're right, my both 3.4 datacenters are using 3.3 level.
I migrated recently.

How safe or risky is it to increase this DC level ?

> 
> regards,
> Maor
> 
> On 06/09/2014 01:06 PM, Nicolas Ecarnot wrote:
>> 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