Xen Storage Motion issues on LVM storage

This issue doesn't affect XenServer 6.5 and previous.

Symptoms: when doing Xen Storage motion on multiple VMs (3 in parallel), to a host with LVM SR (local SR), it fails with INTERNAL_ERROR(Storage_interface.Does_not_exist(_))

When done from a host with LVM to a host with NFS SR, no problem.

Example:

1. Migrating VMs from Lab1 (Pool A) to Lab3 (Pool B). Lab1 has NFS SR, Lab3 Local SR with lvm. This SR is empty and Lab3 doesn't have any VM running on it (see XSO1.png)

2. Migrating 4 VMs from Lab1 to Lab3 (see XSO2.png)

3. Operation in progress (see XSO3.png)

4. When the task is at 100%, we got the error, for each migration: INTERNAL_ERROR(Storage_interface.Does_not_exist(_))

VMs are in suspended state in the origin host and also halted on destination host. Can't boot them on origin host because "no host available", had to force shutdown them. They can boot normally on destination host.

Doing it on the other way (from Lab3 to Lab1), no issues at all (probably because destination SR is NFS).