On 07/29/2015 01:29 PM, Manjong Han wrote: > Thanks, Stefan. > > 2015-07-29 17:46 GMT+09:00 Stefan Hajnoczi <stefa...@gmail.com>: >> >> You should probably use qcow2 backing files instead: >> >> 10G.qcow2 <-- vm001.qcow2 >> ^-- vm002.qcow2 >> >> The command to create these files is: >> >> qemu-img create -f qcow2 -o backing_file=10G.qcow2 vm001.qcow2. >> >> Both VMs share the data in 10G.qcow2. All writes go to vm001.qcow2 or >> vm002.qcow2, respectively, so they don't corrupt each other. >> > > I tried to create a backing files, using the commands which you told. > > $ qemu-img create -f qcow2 -o backing_file=10G.qcow2 vm001.qcow2 > $ qemu-img create -f qcow2 -o backing_file=10G.qcow2 vm002.qcow2 > > And, I used these backing files on each virtual machines. > But, new files weren't written on original disk image(10G.qcow2).. > The backing files were working each other. > >> Standard file systems (ext4, xfs) and volume managers (LVM) are not >> cluster-aware by default. They must only be accessed from one machine >> at a time. Otherwise you risk data corruption. >> > > I think that I must probably use a shared file system like NFS.. >
Yes, any files written using the backing files like outlined above will put new files in the overlays (e.g. vm001.qcow2 or vm002.qcow2) and NOT into the backing file (10G.qcow2) this is a safe way to share a base image for an OS, but it's not a method of accomplishing a concurrent fileshare. You'll want to configure an NFS or CIFS share (etc) in the base image and then allow the multiple VMs to utilize that share. --js
