Add support for QEMU built-in iSCSI initiator

Add support for QEMU built-in iSCSI initiator

https://blueprints.launchpad.net/nova/+spec/qemu-built-in-iscsi-initiator

QEMU has built-in iSCSI initiator using libiscsi and Libvirt can handle it as same as other network storages. This blueprint adds iSCSI support to Nova’s network volume driver (nova.virt.libvirt.LibvirtNetVolumeDriver).

Problem description

Nova already has iSCSI volume driver for KVM/QEMU (nova.virt.libvirt.LibvirtISCSIVolumeDriver), but iSCSI targets for volumes aren’t attached to VMs directly but to the host OS of nova-compute nodes. It means:

  • Storage structure of the host OS will be changed when volumes are attaching to / detaching from VMs on the host. The commands executed by nova-compute to attach/detach volumes are complex. So they may cause confusing storage structure the host OS and make trouble shooting difficult when a problem had occured.

  • The host OS have many system logs on attaching/detaching volumes and tons of error logs if a trouble occurs at the iSCSI target or multipath.

  • The VMs on a compute node will be stopped when an iSCSI volume is attached or detached to a VM and it causes the host OS crash.

Use Cases

  • Using so many iSCSI-based volumes and attached them to many VMs on a host. Say that up to 50 VMs on a host and up to 20 volumes attached to a VM. It means that the host OS will handle up to 1k iSCSI targets by itself with LibvirtISCSIVpolumeDriver and the number will be 2x, 3x, or 4x if you use iSCSI multipath capability.

Project Priority

None

Proposed change

Using KVM/QEMU built-in iSCSI initiator via Libvirt for attaching iSCSI volumes. To do so, we have to implement 2 functionality:

  • Implement a new libvirt XML configuration handler class named LibvirtConfigSecret. It manages information for iSCSI CHAP authentication.

  • Extend LibvirtNetVolumeDriver to support QEMU built-in iSCSI initiator using LibvirtConfigSecret if needed.

Alternatives

Just use LibvirtISCSIVolumeDriver.

Data model impact

None

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

  • QEMU built-in iSCSI initiator doesn’t support multipath capability. So VMs will be not able to handle volumes when iSCSI connections die even if the backend iSCSI storage has multipath capability.

  • QEMU binary of Ubuntu 14.04 doesn’t have iSCSI support. Users have to install libiscsi2 package and libiscsi-dev from Debian and rebuild QEMU binary with libiscsi support by themselves.

Developer impact

None

Implementation

Assignee(s)

Primary assignee:

Akira Yoshiyama <akirayoshiyama@gmail.com>

Work Items

Working patches exist, so we have to:

  • Implement unit tests.

  • Review the codes.

Dependencies

None

Testing

Usually, devstack builds an OpenStack deployment with Cinder using LVMISCSIDriver, so we can use it for basic smoke tests. And we should do more tests with vendor iSCSI drivers.

Documentation Impact

Adding configuration notes to use the driver like below:

To use this, you have to write a parameter at nova.conf:

volume_drivers = iscsi=nova.virt.libvirt.volume.LibvirtNetVolumeDriver,

iser=nova.virt.libvirt.volume.LibvirtISERVolumeDriver,…

or just

volume_drivers = iscsi=nova.virt.libvirt.volume.LibvirtNetVolumeDriver

References

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nova-specs