On 02/09/2016 11:58 AM, Denis V. Lunev wrote: > On 02/09/2016 07:49 PM, John Snow wrote: >> >> On 02/09/2016 09:37 AM, Denis V. Lunev wrote: >>> On 02/09/2016 05:21 PM, Stefan Hajnoczi wrote: >>>> On Fri, Feb 05, 2016 at 11:28:42AM +0300, Denis V. Lunev wrote: >>>>> On 02/03/2016 11:14 AM, Fam Zheng wrote: >>>>>> On Sat, 01/30 13:56, Vladimir Sementsov-Ogievskiy wrote: >>>>>>> Hi all. >>>>>>> >>>>>>> These series which aims to add external backup api. This is needed >>>>>>> to allow >>>>>>> backup software use our dirty bitmaps. >>>>>>> >>>>>>> Vmware and Parallels Cloud Server have this feature. >>>>>> What is the advantage of this appraoch over "drive-backup >>>>>> sync=incremental >>>>>> ..."? >>>>> This will allow third-party vendors to backup QEMU VMs into >>>>> their own formats or to the cloud etc. >>>> Backup software can implement NBD to receive the incremental blocks >>>> from >>>> QEMU. Use drive-backup sync=incremental and the backup appliance as >>>> the >>>> NBD target. >>>> >>>> It's more complicated to add this QMP command flow to backup software >>>> than to implement NBD. >>>> >>>> Stefan >>> it can, but this is a matter of problem due to the nature of >>> how this software is implemented. Usually it is written >>> in a semi-standard way and it uses "plugins" to actually >>> collect the data, i.e. the code is written in standard >>> interface/real implementation pattern and interfaces are >>> basically the same. >>> >>> With this standard approach backup software is working >>> as an active side of the process, i.e. it performs operations >>> and controls the flow. >>> >>> This means that "non-standard" QEMU technology will be >>> pain here. >>> >>> Den >> Am I to understand that for e.g. VMWare the backup appliance is >> literally reading the disk image from storage directly while the VM is >> running? >> >> I'd be a bit surprised if that were true. > I think that backup software is asking alive VM about the data. > >> My biggest concern here is that there is not a safe way, today, to read >> from a disk image atomically while the VM is running. I think that'd >> take a lot of work to do and you'll not find a lot of support in >> implementing it. >> >> Of course, while the VM is paused/off is a different story, but for now >> I still feel like NBD is the right answer for getting block data from >> QEMU. >> >> What am I missing? >> >> --js > In general, in Parallels Server the backup was created using the > following approach: > - create external snapshot. In this case the base image (backing store > in QEMU terminology) > will be READ-ONLY and could be safely read by any entity > - backup that read-only disk image (any way) > - merge snapshots >
I see. > In this process backup software is active while PCS is passive. PCS? > With QEMU the approach looks the same to me: > - start a backup > - ask QEMU to give a data to be backuped (using NBD server in QEMU > with Fam's image fleecing) > - finish backup > > Important bit here is that dirty bitmap should be provided > by QEMU by request. This dirty bitmap will be read-only at that > moment, current active dirty bitmap should be replaced with > new at backup start operation. > > Den I don't have any problems providing the bitmap data through an external API, but the part I want to be 100% clear on before I ACK it is the API portion where we allow an external client to split or merge bitmaps externally -- that's functionality you don't need if you query the data from QEMU itself. If using NBD (either through the incremental backup tool or image fleecing) that is completely fine, too. My only reservations are over making direct reads to image files outside of QEMU while the VM is running. --js
