In general, abstracting the offload of snapshot, backup etc the a SAN is exactly the job of cinder.
RDM has, in the general cloud case, a bunch of security issues (raw sector reads outside of what is being presented, firmware updates, etc) that need carefully looking at. On 18 March 2014 09:33, Zhangleiqiang (Trump) <zhangleiqi...@huawei.com> wrote: >> From: Huang Zhiteng [mailto:winsto...@gmail.com] >> Sent: Tuesday, March 18, 2014 4:40 PM >> 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 11:01 AM, Zhangleiqiang (Trump) >> <zhangleiqi...@huawei.com> wrote: >> >> From: Huang Zhiteng [mailto:winsto...@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) >> >> <zhangleiqi...@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? > > Thanks for your reply. > > The advantages of Raw device mapping are all introduced by its capability of > "pass" scsi command to the device, and the most common use cases are > clustering and performance improvement mentioned above. > > And besides these two scenarios, there is another use case: running SAN-aware > application inside instances, such as: > 1. SAN management app > 2. Apps which can offload the device related works, such as snapshot, backup, > etc, to SAN. > > >> > >> >> > 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-dri >> >> > ver >> >> > ---------- >> >> > zhangleiqiang (Trump) >> >> > >> >> > Best Regards >> >> > >> >> > _______________________________________________ >> >> > OpenStack-dev mailing list >> >> > OpenStack-dev@lists.openstack.org >> >> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev >> >> >> >> >> >> >> >> -- >> >> Regards >> >> Huang Zhiteng >> >> >> >> _______________________________________________ >> >> OpenStack-dev mailing list >> >> OpenStack-dev@lists.openstack.org >> >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev >> > _______________________________________________ >> > OpenStack-dev mailing list >> > OpenStack-dev@lists.openstack.org >> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev >> >> >> >> -- >> Regards >> Huang Zhiteng >> >> _______________________________________________ >> OpenStack-dev mailing list >> OpenStack-dev@lists.openstack.org >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > _______________________________________________ > OpenStack-dev mailing list > OpenStack-dev@lists.openstack.org > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev -- Duncan Thomas _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
