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@@ -9,24 +9,42 @@ Example of a migration
 
 ## Sources
 
+Silo storage sources.
+
 * File source
 * Memory source
 
 ## Modules
 
-| Module | Description |
-| ------ | ----------- |
-| ArtificialLatency  | Adds a fixed latency to reads / writes for testing/benchmarking.            |
-| Cache | This contains a source, and a store of what data is contained in the cache. If the data is not in the cache for a read, a cache miss error is returned. |
-| DirtyTracker | This tracks write operations for some period, so we know which areas of the source are dirty. |
+Modules can be chained together to create various storage workflows / setups.
+
+| Module                | Description |
+| --------------------- | ----------- |
+| ArtificialLatency     | Adds a fixed latency to reads / writes for testing/benchmarking.            |
+| Cache                 | This contains a source, and a store of what data is contained in the cache. If the data is not in the cache for a read, a cache miss error is returned. |
+| DirtyTracker          | This tracks write operations for some period, so we know which areas of the source are dirty. |
 | FilterRedundantWrites | This can filter out any redundant writes (Write data is same as source data), and can also cut large writes into smaller writes which only contains changed data. |
-| Lockable | This can lock a source for some period. |
-| Metrics | General metrics module to track read/write ops,bytes and latency |
-| Nothing | Empty module - /dev/null |
-| ShardedStorage | This shards storage into multiple storage, which for example allows concurrent writes across shards. |
-| Splitter | This allows the insertion of cache type sources. Any cache hit reads return immediately, whilst misses result in a read from the source, which then also gets written to any of the cache type sources.
+| Lockable              | This can lock a source for some period. |
+| Metrics               | General metrics module to track read/write ops,bytes and latency |
+| Nothing               | Empty module - /dev/null |
+| ReadDirtyTracker      | Similar to a DirtyTracker, but only starts tracking writes to a block after it's been read ONCE. |
+| ShardedStorage        | This shards storage into multiple storage, which for example allows concurrent writes across shards. |
+| Splitter              | This allows the insertion of cache type sources. Any cache hit reads return immediately, whilst misses result in a read from the source, which then also gets written to any of the cache type sources. |
+| VolatilityMonitor     | This tracks writes to blocks, and implements BlockOrder - it returns blocks in least volatile to most volatile order. |
+| WaitingCache          | With this cache, reads WAIT until a write to all blocks concerned have taken place. |
+
+## BlockOrder
 
+BlockOrder allows specifying black order in migration. They can be chained together.
+
+| BlockOrder            | Description |
+| --------------------- | ----------- |
+| AnyBlockOrder         | This returns blocks in any order. |
+| PriorityBlockOrder    | This returns blocks in the order they were given priority, and then will defer to next() |
+| VolatilityMonitor     | THis returns blocks from least volatile to most volatile. |
 
 ## Expose
 
+These expose a silo storage as a device.
+
 * NBD device
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