In the meantime, here it is!
Checkpointing a Domain with xm save
As we mentioned previously, xm save halts a domain in the process of writing its internal state to a save file, and rebuilds it entirely when the save file is restored. With recent versions of Xen, however, the save command supports an option to keep the machine running after it's been saved - a feature called "checkpointing."
Checkpoint a domain thus:
# xm save -c <domain> <checkpoint file>
After the checkpoint's been saved, the domain will continue running.
Although the principle of checkpointing seems simple, it's tricky to actually get it to work in practice. The problem is that the running domain will continue to modify its storage, which causes the saved state to be out of sync with the backing store.
To
avoid this problem, you can use a script that hooks into Xen's
external device migration framework to checkpoint the domain storage
during the save process, as described in the textbox.
[textbox title: Device Migration Hooks]
Xen includes the option of calling an external device migration script at each step of a save or migrate. Although the feature was originally added for the sake of TPM migration, it's since been extended to migrating arbitrary devices.
Enable the external-device-migrate script by setting the external-migration-tool directive in /etc/xen/xend-config.sxp. Most likely you'll want to set (external-migration-tool 'external-device-migrate') and let that script source appropriate scripts for external devices.
[end textbox]
