One of the main challenges of centralised social networks is having a central provider that stores the data which imposes some limitations to preserve the privacy of users' data. However, one of the decentralised architectures is peer-to-peer network that every user takes the responsibility of storing and managing his/her data. Although the privacy of data is increased in these networks, authorised friends must have access to the shared data when the user is not online in the network. For this

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... urpose, the user selects some friends and copies his/her data in their space. On the other hand, the amount of used space and the total number of replicas must be reduced as much as possible. In this study, the authors provide some solutions to reduce the amount of used space and the total number of replicas to increase data availability. In this way, they segment the user's data and consider the stability of copy-location, i.e. the selected friends who have a copy of the user's data. The performance evaluation of the proposed methods shows that they considerably reduce the amount of used space as well as the total number of replicas in comparison to other approaches. Nomenclature RU x responsible users for user x's data availability Friend x friends of user x Score ix score related to user i (i is friend with x) AS x available (free) storage related to user x RD x storage needed for recent shared data of user x OD x storage needed for other shared data of user x: Data x = RD x + OD x MNR maximum number of replicas (RU) for each user AvlF ix provided availability by friend i for user x (i ∈ RU x ) AvlU x availability of user x EUA expected user availability EFA expected friend availability pool all nodes with their score