Re: [Qemu-devel] Taking live snapshots of running VMs
On 07/09/11 00:24, Ahmed M. Azab wrote: Hi All, Is there a way to take a live memory snapshot of a running VM without freezing or stopping this VM? I explored the Qemu code and documentation and I found two ways to take a snapshot: What you are talking about is called a 'checkpoint', not a snapshot. There has been a lot of confusion around the naming, but it really helps if we try to use the right names. Checkpoints are for things you want to be able to restart, ie. with memory, snapshots are just data, ie. disks. Cheers, Jes
Re: [Qemu-devel] Taking live snapshots of running VMs
Am 09.07.2011 00:24, schrieb Ahmed M. Azab: Hi All, Is there a way to take a live memory snapshot of a running VM without freezing or stopping this VM? I explored the Qemu code and documentation and I found two ways to take a snapshot: 1-Using savevm Qemu monitor command, which freezes the VM for tens of seconds 2-Using migrate and select the destination as a file, which forces the machine to stop after the snapshot is saved. In production environments (where delaying the operations of a VM is very critical), it is always useful to take memory snapshots to do system analysis or forensics. I think Qemu should provide a way to take a snapshot based on QOW technque of memory pages (same as the QCOW disk snapshoting). If such technique does not exist, I am willing it devlop it myself, but I wonder if the Qemu community will be interested to add my patch to future versions. All the code that deals with memory is already there and used for migration. I think what you really need is a combination of savevm and live migration, such that you live migrate the VM state into the qcow2 image and when the migration has completed, you take a disk snapshot and continue the VM. It shouldn't be too hard to do this. All of the building blocks are there, they just need to be combined in the right way. I would be interested in a patch allowing this. Having said that, I think there are more variations that we'll want to support. Basically the dimensions that I see are: 1. Disk-only vs. complete VM state 2. Store VM state internally in qcow2 vs. an external file 3. Use internal vs. external disk snapshots Ideally, we would allow users to choose freely. For example, internal disk snapshot with external VM state is a combination that I think could be very useful. Kevin
Re: [Qemu-devel] Taking live snapshots of running VMs
On Sat, Jul 9, 2011 at 05:24, Ahmed M. Azab ama...@ncsu.edu wrote: Hi All, Is there a way to take a live memory snapshot of a running VM without freezing or stopping this VM? something like what Xen does with live migration by using incremental page migration (or something named like that?)? -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com
Re: [Qemu-devel] Taking live snapshots of running VMs
On Fri, Jul 8, 2011 at 11:24 PM, Ahmed M. Azab ama...@ncsu.edu wrote: Is there a way to take a live memory snapshot of a running VM without freezing or stopping this VM? You could add a bit of code that forks QEMU. The kernel does memory copy-on-write across fork(2). Make sure not to use file-backed/shared memory for guest RAM (but that's okay since it is the default). The child process could write out the memory image and then terminate - or it could sit around waiting for you to inspect it with GDB or some other mechanism. If you kill the child process then you lose access to that memory snapshot. For production I'm not convinced that this feature is useful. There is already support for crash dumping and kernel debugging of guest OSes. The mechansim various by guest OS, but it works similar to on a physical machine. What system analytics or forensics exactly are useful when you only have access to guest *physical* memory? Seems like a development feature that you can hack on locally in a few lines of code but not something for production. Stefan
[Qemu-devel] Taking live snapshots of running VMs
Hi All, Is there a way to take a live memory snapshot of a running VM without freezing or stopping this VM? I explored the Qemu code and documentation and I found two ways to take a snapshot: 1-Using savevm Qemu monitor command, which freezes the VM for tens of seconds 2-Using migrate and select the destination as a file, which forces the machine to stop after the snapshot is saved. In production environments (where delaying the operations of a VM is very critical), it is always useful to take memory snapshots to do system analysis or forensics. I think Qemu should provide a way to take a snapshot based on QOW technque of memory pages (same as the QCOW disk snapshoting). If such technique does not exist, I am willing it devlop it myself, but I wonder if the Qemu community will be interested to add my patch to future versions. Ahmed
