| Let's say we have an LV, made up of three segments of different PV's, |
| I've also added in the device major:minor as this will be useful |
| later: |
| |
| +-----------------------------+ |
| | PV1 | PV2 | PV3 | 254:3 |
| +----------+---------+--------+ |
| |
| |
| Now our hero decides to PV move PV2 to PV4: |
| |
| 1. Suspend our LV (254:3), this starts queueing all io, and flushes |
| all pending io. Once the suspend has completed we are free to change |
| the mapping table. |
| |
| 2. Set up *another* (254:4) device with the mapping table of our LV. |
| |
| 3. Load a new mapping table into (254:3) that has identity targets for |
| parts that aren't moving, and a mirror target for parts that are. |
| |
| 4. Unsuspend (254:3) |
| |
| So now we have: |
| destination of copy |
| +--------------------->--------------+ |
| | | |
| +-----------------------------+ + -----------+ |
| | Identity | mirror | Ident. | 254:3 | PV4 | |
| +----------+---------+--------+ +------------+ |
| | | | |
| \/ \/ \/ |
| +-----------------------------+ |
| | PV1 | PV2 | PV3 | 254:4 |
| +----------+---------+--------+ |
| |
| Any writes to segment2 of the LV get intercepted by the mirror target |
| who checks that that chunk has been copied to the new destination, if |
| it hasn't it queues the initial copy and defers the current io until |
| it has finished. Then the current io is written to *both* PV2 and the |
| PV4. |
| |
| 5. When the copying has completed 254:3 is suspended/pending flushed. |
| |
| 6. 254:4 is taken down |
| |
| 7. metadata is updated on disk |
| |
| 8. 254:3 has new mapping table loaded: |
| |
| +-----------------------------+ |
| | PV1 | PV4 | PV3 | 254:3 |
| +----------+---------+--------+ |
