Open Stack

On Tue, Mar 18, 2014 at 9:40 AM, Zhangleiqiang (Trump)
<zhangleiqiang at huawei.com> wrote:
> 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.
If 'clustering' here refers to things like cluster file system, which
requires LUNs to be connected to multiple instances at the same time.
And since you mentioned Cinder, I suppose the LUNs (volumes) are
managed by Cinder, then you have an extra dependency for multi-attach
feature: https://blueprints.launchpad.net/cinder/+spec/multi-attach-volume.
>         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.
It seems to me that the performance benefit mostly from virtio-scsi,
which is just an virtual disk interface, thus should also benefit all
virtual disk use cases not just raw device mapping.
>
>         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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-- 
Regards
Huang Zhiteng