Hi, stackers：
With RDM, the storage logical unit number (LUN) can be directly
connected to a instance from the storage area network (SAN).
For most data center applications, including Databases, CRM and ERP
applications, RDM can be used for configurations involving clustering between
instances, between physical hosts and instances or where SAN-aware applications
are running inside a instance.
RDM, which permits the use of existing SAN commands, is generally used
to improve performance in I/O-intensive applications and block locking.
Physical mode provides access to most hardware functions of the storage system
that is mapped.
For libvirt driver, RDM feature can be enabled through the "lun" device
connected to a "virtio-scsi" controller:
<disk type='block' device='lun'>
<driver name='qemu' type='raw' cache='none'/>
<source dev='/dev/mapper/360022a110000ecba5db427db00000023'/>
<target dev='sdb' bus='scsi'/>
<address type='drive' controller='0' bus='0'/>
</disk>
<controller type='scsi' index='0' model='virtio-scsi'/>
Currently，the related works in OpenStack as follows:
1. block-device-mapping-v2 extension has already support the "lun"
device with "scsi" bus type listed above, but cannot make the disk use
"virtio-scsi" controller instead of default "lsi" scsi controller.
2. libvirt-virtio-scsi-driver BP ([1]) whose milestone target is
icehouse-3 is aim to support generate a virtio-scsi controller when using an
image with "virtio-scsi" property, but it seems not to take boot-from-volume
and attach-rdm-volume into account.
I think it is meaningful if we provide the whole support for RDM
feature in OpenStack.
Any thoughts? Welcome any advices.
[1] https://blueprints.launchpad.net/nova/+spec/libvirt-virtio-scsi-driver
----------
zhangleiqiang (Trump)
Best Regards
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