Open Stack

On Tue, Mar 18, 2014 at 11:01 AM, Zhangleiqiang (Trump)
<zhangleiqiang at huawei.com> wrote:
>> 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
>> Mapping
>>
>> 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.

Set clustering use case and performance improvement aside, what other
benefits/use cases can RDM bring/be useful for?
>
>> >         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
>> >
>> > _______________________________________________
>> > OpenStack-dev mailing list
>> > OpenStack-dev at lists.openstack.org
>> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
>>
>>
>>
>> --
>> Regards
>> Huang Zhiteng
>>
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-- 
Regards
Huang Zhiteng