Hi, I have a block storage which I only want to be mounted on a single node. I know that there are many possibilities for shared storage usage but I want to know if the following is possible (using the API). - Have a domain running on node-A - Initialize a migration for that domain to node-B - Run a hook or something just before the domain starts on node-B to: - unmount storage on node-A - mount/prepare storage on node-B Thanks and best regards, Etienne
On Tue, Aug 01, 2023 at 12:28:56 +0200, e-m@mailbox.org wrote:
Hi,
I have a block storage which I only want to be mounted on a single node. I know that there are many possibilities for shared storage usage but I want to know if the following is possible (using the API). - Have a domain running on node-A - Initialize a migration for that domain to node-B - Run a hook or something just before the domain starts on node-B to: - unmount storage on node-A - mount/prepare storage on node-B
This is not possible with qemu, because during migration the process running the VM exists both on node-A and node-B, and has the storage open (although not accessing it) from both sides. At the time the migration is switching over, the source flushes buffers and the destination starts writing into the image. This means that the storage must be mounted on both nodes during the migration. What you can do though is, to save the VM state into a file and restore it on the other node. (virsh save, virsh restore). Which uses basically the same approach as migration, but the VM state is dumped to a file and preserved, thus you can umount the storage for the necessary time until it's moved to the next node.
Hello, Also here is a related issue to create an additional hook during migration in order to deal with volume preparation on the source node. https://gitlab.com/libvirt/libvirt/-/issues/37 2 août 2023 14:18:42 Peter Krempa <pkrempa@redhat.com>:
On Tue, Aug 01, 2023 at 12:28:56 +0200, e-m@mailbox.org wrote:
Hi,
I have a block storage which I only want to be mounted on a single node. I know that there are many possibilities for shared storage usage but I want to know if the following is possible (using the API). - Have a domain running on node-A - Initialize a migration for that domain to node-B - Run a hook or something just before the domain starts on node-B to: - unmount storage on node-A - mount/prepare storage on node-B
This is not possible with qemu, because during migration the process running the VM exists both on node-A and node-B, and has the storage open (although not accessing it) from both sides.
At the time the migration is switching over, the source flushes buffers and the destination starts writing into the image.
This means that the storage must be mounted on both nodes during the migration.
What you can do though is, to save the VM state into a file and restore it on the other node. (virsh save, virsh restore). Which uses basically the same approach as migration, but the VM state is dumped to a file and preserved, thus you can umount the storage for the necessary time until it's moved to the next node.
participants (3)
-
e-m＠mailbox.org -
Guy Godfroy -
Peter Krempa