[ovirt-users] Host non operationnal due to an iSCSI problem

[Alex Crow]

On 19/07/16 11:13, Alexis HAUSER wrote:
>> I don't understand. iSCSI is a network storage protocol. What do you
>> mean by "I access it directly"? When you set up the first host with an
>> iSCSI storage domain, you would have had to point it to an IP address,
>> "discover" the LUNs and then attach to them. This sets up the domain.
> As I explained, I don't use an iSCSI server, that's what I call accessing it "directly".
> Yes, my iSCSI storage is working on my first Host, it has been discovered successfully, some VM are working on it etc...
> The second host can discover it so I don't think it's a network issue.
>
>  From the vdsm logs from second host ("the non working one") it looks like it can even see the LVM on it, right ?
>
> Thread-32::DEBUG::2016-07-19 08:41:37,935::lvm::290::Storage.Misc.excCmd::(cmd) FAILED: <err> = '  Volume group "091e0526-1ff3-4ca3-863c-b911cf69277b" not found\n  Cannot process volume group 091e0526-1ff3-4ca3-863c-b911cf69277b\n'; <rc> = 5
>

It knows there there are volume groups from the database. You are 
correct, in that it cannot access the VGs/LVs.
>
>> On the second host, to access iSCSI storage you will have to have an
>> interface (defined in "Networks" in oVirt) that can connect to the same
>> IP and port the first host used.
> Yes I have an network interface working on the second host, which is ovirtmgmt. I can access all other storage correctly from that host without errors. I can discover the iSCSI.
>
> As it is a multipath iSCSI, does it need to acces one different path for each host ? I didn't set anything about iSCSI bonding, I use only one single interface on each host.

I'm still finding this hard to understand. If you are using iSCSI, you 
/are/ using a server (called the "Target" in SCSI speak). Is the iSCSI 
storage actually on the first host? How did you actually do the 
discovery and assign the LUNs? In the storage domain properties you 
should be able to see the IP and port of the Targets, something like 
"iqn.2012-02:foo-target1,192.168.10.10,3260", and you need to ensure the 
second host can reach that IP and port to be able to see the storage.

Multipath should not make any difference right now, but in order to use 
it effectively you should probably set up an iSCSI bond. The requirement 
for multipath to work properly is that the two physical interfaces on 
the host and initiator are in different IP subnets (and should ideally 
travel via different switches but that is not a hard requirement).

If you only have one physical interface on each host, there's not much 
point doing multipath, as you don't stand to gain any performance or 
resilience.

Cheers

Alex
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