KVM and Xen Disk Management Parity

This is feedback from the session at the Essex Summit to achieve disk management parity between KVM and XenServer and to provide the model for other hypervisors to be compatible in how they manage disk images within the hypervisor.

The amenable solution agreed upon at the summit was to add a second disk column to the instances_type table. This would allow service providers to have different operating systems configured differently and provide a consistent view across OpenStack. Using python-novaclient, a current nova flavor-list returns the following fields.

+----+--------------+-----------+------+----------+-------+------------+----------+
| ID | Name | Memory_MB | Swap | Local_GB | VCPUs | RXTX_Quota | RXTX_Cap |
+----+--------------+-----------+------+----------+-------+------------+----------+

By adding an additional disk field, operators would be able to utilize this field to show customers how the disks would be configured between instance-types. For example:

+----+--------------+-----------+------+----------+-------+------------+----------+
| ID | Name | Memory_MB | Swap | Local_GB | VCPUs | RXTX_Quota | RXTX_Cap |
+----+--------------+-----------+------+----------+-------+------------+----------+
| 1 | 256 slice | 256 | 0 | 10 | 1 | 150 | 10 |
| 2 | 512 slice | 512 | 0 | 20 | 1 | 300 | 20 |

Could be represented as:

+----+--------------+-----------+------+----------+-------+------------+----------+
| ID | Name | Memory_MB | Swap | Disk1_GB | Disk2_GB| VCPUs | RXTX_Quota | RXTX_Cap |
+----+--------------+-----------+------+----------+-------+------------+----------+
| 1 | 256 slice | 256 | 0 | 10 |30 | 1 | 150 | 10 |
| 2 | 512 slice | 512 | 0 | 20 |60 | 1 | 300 | 20 |
| 3 | 256 slice | 256 | 0 | 40 |0 | 1 | 150 | 10 |
| 4 | 512 slice | 512 | 0 | 80 |0 | 1 | 300 | 20 |

In the above example, ID 1 would have a primary disk of 10gb allocated and a secondary disk of 30gb allocated. if the user resized to ID 2, both the primary and the secondary partition would grow accordintly. If the user then resized to ID 3, the primary disk would grow to 40gb and the secondary disk would be dropped from their configuration.

***The secondary disk would be considered ephemeral and would not be included in system snapshots or included in the disk images coming from Glance. ***