[Qemu-devel] [PATCH 0/3] sheepdog: support online snapshot from qemu-img
Currently, we can take sheepdog snapshots of running VMs only from the qemu monitor. This series allows taking online snapshots from qemu-img. The first two patches prepare for the thrid patch. MORITA Kazutaka (3): sheepdog: cleanup find_vdi_name sheepdog: add SD_RES_READONLY result code sheepdog: resend write requests when SD_RES_READONLY is received block/sheepdog.c | 115 ++ 1 files changed, 107 insertions(+), 8 deletions(-) -- 1.7.2.5
Re: [Qemu-devel] [PATCH 0/3] sheepdog: support online snapshot from qemu-img
On 04/25/2013 04:37 AM, MORITA Kazutaka wrote: Currently, we can take sheepdog snapshots of running VMs only from the qemu monitor. This series allows taking online snapshots from qemu-img. Is that even safe? We specifically recommend that users NOT use qemu-img on any image that is in-use by a qemu process, and instead only use qemu monitor commands; since qemu-img may see inconsistent state, and worse, any writes that qemu-img do may cause qemu to see inconsistent state and cause corruption to the running guest. -- Eric Blake eblake redhat com+1-919-301-3266 Libvirt virtualization library http://libvirt.org signature.asc Description: OpenPGP digital signature
Re: [Qemu-devel] [PATCH 0/3] sheepdog: support online snapshot from qemu-img
On Thu, Apr 25, 2013 at 07:44:29AM -0600, Eric Blake wrote: On 04/25/2013 04:37 AM, MORITA Kazutaka wrote: Currently, we can take sheepdog snapshots of running VMs only from the qemu monitor. This series allows taking online snapshots from qemu-img. Is that even safe? We specifically recommend that users NOT use qemu-img on any image that is in-use by a qemu process, and instead only use qemu monitor commands; since qemu-img may see inconsistent state, and worse, any writes that qemu-img do may cause qemu to see inconsistent state and cause corruption to the running guest. It's safe in the same way that multiple hosts can access the same NFS export. All I/O is going through the same NFS server and is therefore kind of consistent ;). The problem that qcow2 has is that two programs would overwrite metadata in the file, possibly stepping on each other's feet and corrupting the image metadata. Sheepdog can handle snapshot requests coming from different clients. Users can still shoot themselves in the foot if they start doing things like reading or writing image data while the guest is running. Stefan
