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codex/slot-dispersal.md

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+---
+title: CODEX-SLOT-DISPERSAL
+name: Codex SLOT Dispersal
+status: raw
+tags: codex
+editor: 
+contributors:
+---
+
+## Abstract
+
+This specification describes a method used by the Codex network for node dispersal for filling slot request.
+To achieve a truely decentralized storage network, data being stored on mutlple nodes should be prioritized.
+
+## Motivation
+Client nodes benefit from resilient data storage when multiple nodes are storing their requested data.
+In a distbuted storage solution, 
+a storage marketplace allows storage providers the ability to announce storage availability and
+storage request to find hosting.
+High performance nodes may have an advantage over a majority of nodes participating in the marketplace as storage requests may always choose the high proformance nodes to store data.
+This creates a centralized scenario as only high performance nodes will participate 
+and be rewarded in the network. 
+
+The Codex network does not implement a first come, first serve method to avoid centralized behaviors.
+Instead, the Codex network encourages storage requests to allow only a select few storage providers to create a storage contracts with the client node requests.
+
+## Specification
+The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [2119](https://www.ietf.org/rfc/rfc2119.txt).
+
+Storage providers compete with one another to store data from storage request.
+Before a storage providers can download the data, 
+they MUST be selected to obtain a reseversation of a slot.
+
+The Codex network using Kademlia distance function to select eligible  storage providers per slot.
+This starts with a random source address hash contructed as:
+
+    hash(blockHash, requestId, slotIndex, reservationIndex)
+
+`blockHash`: 
+
+`requestId`:
+
+`slotIndex`:
+
+`reservationIndex`:
+
+The source address is used along with the storage provider's blockchain address to calculate the Kademlia distance.
+This is represented by:
+
+$$ XOR(A,A_0) $$
+
+
+The allowed distance over time $t_1$, can be defined as $2^{256} * F(t_1)$.
+When the storage provider's distance is greater than the allowed distance,
+the storage provider SHOULD be eligible to to obtain a slot reservation.
+- Note after eligiblity, the storage provider MUST provide token collateral and storage proofs to make change the state of a slot from a reserved state to a filled state, see [slots](https://github.com/vacp2p/rfc-index/blob/codex-marketplace/codex/marketplace.md#slots).
+
+### Filling Slot
+
+When the value of the allowed distance increases,
+more storage providers SHOULD be elgiblable to participate in reserving a slot.
+The Codex network allows a storage provider is allowed to fill a slot after calculating the storage provider's Kademlia distance is less than the allowed distance.
+The total value storage providers MUST obtain can be defined as:
+
+$$ XOR(A,A_0) < 2^{256} * F(t_1) $$
+
+Eligible storage providers represented below:
+
+                             start point
+                                  |           Kademlia distance
+            t=3    t=2    t=1     v
+      <------(------(------(------·------)------)------)------>
+                      ^                            ^
+                      |                            |
+                 this provider is               this provider is
+                  allowed at t=2                 allowed at t=3
+
+## Copyright
+
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
+
+## References
+1. [slots](https://github.com/vacp2p/rfc-index/blob/codex-marketplace/codex/marketplace.md#slots)
+
+