<div dir="ltr"><div>QEMU has the ability to directly connect to iSCSI volumes. Running the iSCSI connections through the nova-compute host *seems* somewhat inefficient. </div><div><br></div><div>There is a spec/blueprint and implementation that landed in Kilo:</div><div><br></div><div><a href="https://specs.openstack.org/openstack/nova-specs/specs/kilo/implemented/qemu-built-in-iscsi-initiator.html">https://specs.openstack.org/openstack/nova-specs/specs/kilo/implemented/qemu-built-in-iscsi-initiator.html</a><br></div><div><a href="https://blueprints.launchpad.net/nova/+spec/qemu-built-in-iscsi-initiator">https://blueprints.launchpad.net/nova/+spec/qemu-built-in-iscsi-initiator</a><br></div><div><br></div><div>From looking at the OpenStack Nova sources ... I am not entirely clear on when this behavior is invoked (just for Ceph?), and how it might change in future. </div><div><br></div><div>Looking for a general sense where this is headed. (If anyone knows...)</div><div><br></div><div>If there is some problem with QEMU and directly attached iSCSI volumes, that would explain why this is not the default. Or is this simple inertia?</div><div><br></div><div><br></div><div>I have a concrete concern. I work for a company (EMC) that offers backup products, and we now have backup for instances in OpenStack. To make this efficient, we need to collect changed-block information from instances. </div><div><br></div><div>1) We could put an intercept in the Linux kernel of the nova-compute host to track writes at the block layer. This has the merit of working for containers, and potentially bare-metal instance deployments. But is not guaranteed for instances, if the iSCSI volumes are directly attached to QEMU.</div><div><br></div><div>2) We could use the QEMU support for incremental backup (first bit landed in QEMU 2.4). This has the merit of working with any storage, by only for virtual machines under QEMU.</div><div><br></div><div>As our customers are (so far) only asking about virtual machine backup. I long ago settled on (2) as most promising. </div><div><br></div><div>What I cannot clearly determine is where (1) will fail. Will all iSCSI volumes connected to QEMU instances eventually become directly connected? </div><div><br></div><div><br></div><div>Xiao's unanswered query (below) presents another question. Is this a site-choice? Could I require my customers to configure their OpenStack clouds to always route iSCSI connections through the nova-compute host? (I am not a fan of this approach, but I have to ask.)</div><div><br></div><div>To answer Xiao's question, can a site configure their cloud to *always* directly connect iSCSI volumes to QEMU?</div><div><br></div><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Feb 16, 2016 at 4:54 AM, Xiao Ma (xima2) <span dir="ltr"><<a href="mailto:xima2@cisco.com" target="_blank">xima2@cisco.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
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<div>Hi, All</div>
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<div>I want to make the qemu communicate with iscsi target using libiscsi directly, and I </div>
<div>followed <a href="https://review.openstack.org/#/c/135854/" target="_blank">https://review.openstack.org/#/c/135854/</a> to add </div>
<div><span style="background-color:rgb(255,255,255)">'</span><span style="background-color:rgb(255,255,255)"><font face="monospace" size="2"><span style="white-space:pre-wrap">volume_drivers
= iscsi=nova.virt.libvirt.volume.LibvirtNetVolumeDriver’</span></font> in </span>nova.conf</div>
<div> and then restarted nova services and cinder services, but still the volume configuration of vm is as bellow:</div>
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<div> <disk type='block' device='disk'></div>
<div> <driver name='qemu' type='raw' cache='none'/></div>
<div> <source dev='/dev/disk/by-path/ip-10.75.195.205:3260-iscsi-iqn.2010-10.org.openstack:volume-076bb429-67fd-4c0c-9ddf-0dc7621a975a-lun-0'/></div>
<div> <target dev='vdb' bus='virtio'/></div>
<div> <serial>076bb429-67fd-4c0c-9ddf-0dc7621a975a</serial></div>
<div> <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/></div>
<div> </disk></div>
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<div>I use centos7 and Liberty version of OpenStack.</div>
<div>Could anybody tell me how can I achieve it?</div>
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<div>Thanks.</div></div></div></div></div></blockquote></div></div></div>