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