Understanding iSCSI in Openstack

On May 10, 2011, at 11:15 AM, Matthew Hahn wrote:

> New question #156930 on OpenStack Compute (nova):
> https://answers.launchpad.net/nova/+question/156930
>
> Hey, we got Nova, Glance, and Swift setup. Everything seems to be working with starting instances. Now we are trying to setup iSCSI so that we can present extra storage to the instances. I am trying to understand how Openstack handles iSCSI. However, the documentation seems kind of vague. I have a couple of questions.
>
> First, how do the iSCSI LUNs get presented to the instances? Does the compute node present the iSCSI LUN to the instance via KVM? Or does the instance talk to the nova-volume service directly via iSCSI to get the volume?

In KVM, the compute host attaches to the iscsi target and presents the disk to the guest as a local block device
>
> Second, I am not understanding the –iscsi_ip_prefix argument in nova.conf. What exactly is this flag used for? What network should we specify here?

During the discovery process, iscsiadm reports all of the ips that the target is exposed on. The prefix is matched against the possible IPs so that it knows which IP to connect to. It just uses simple string matching, so if all of your hosts are on the 192.168.1.0/24 network you could use --iscsi_ip_prefix=192.168.1

This code is a bit hacky, and it will probably be converted to actually store the ip in the database so the discovery doesn't have to happen.

>
>
> Thanks,
> Matt
>
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