On Fri, Apr 19, 2013 at 6:11 AM, Yaodong Yang <yaodong.ya...@gmail.com> wrote: > Could someone share me with some information about the live block migration > strategy in the current qemu-kvm. As I know, there are at least IO > mirroring, dirty block tracking, snapshot, precopy or postcopy strategy > exist for the block migration.
migrate -b is the traditional "block migration" feature in qemu-kvm. It copies the contents of a block device as part of the live migration stream. This is a pre-copy approach using a dirty bitmap. It is being replaced by more flexible alternatives. block-stream can be used for pre- and post-copy migration. It creates a new image file that uses the old disk image as its backing file. The contents of the backing file are copied into the new image unless new blocks have already been written in the new image. It requires NFS, NBD, or another mechanism to access both the new image and the backing file at the same time. It is not part of the live migration stream. drive-mirror is even more flexible; one way to use it is to pre-copy the contents of the disk to the destination host. It does not use backing files to achieve this, so the destination image can be any image format. Again, it requires NFS, NBD, or another mechanism to access both the new image and the old image. It is not part of the live migration stream. An advantage of the mirroring approach over block-stream is that you can continue running the old image if there is a power failure or crash during mirroring - simply discard the new image and start over. Stefan
