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From: | Denis V. Lunev |
Subject: | Re: [Qemu-devel] [PATCH v2 0/6] external backup api |
Date: | Tue, 9 Feb 2016 19:58:19 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 |
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. Stefanit 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. DenAm 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 In this process backup software is active while PCS is passive. 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
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