[openstack-dev] [Nova][Cinder] Feature about Raw Device Mapping
zhangleiqiang at huawei.com
Tue Mar 18 03:01:35 UTC 2014
> From: Huang Zhiteng [mailto:winston.d at gmail.com]
> Sent: Tuesday, March 18, 2014 10:32 AM
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] [Nova][Cinder] Feature about Raw Device
> 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.
Yes. "Clustering" include Oracle RAC, MSCS, etc. If they want to work in instance-based cloud environment, RDM and multi-attached-volumes are both needed.
But RDM is not only used for clustering, and haven't dependency for 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
> > <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 () 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.
> > 
> > https://blueprints.launchpad.net/nova/+spec/libvirt-virtio-scsi-driver
> > ----------
> > zhangleiqiang (Trump)
> > Best Regards
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> Huang Zhiteng
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