Trong vài năm gần đây, ngành công nghiệp đã nhiều thị trường một loạt các nguyên tắc mới cho thiết kế kiểu mô-đun hệ thống doanh nghiệp theo tên của kiến trúc hướng dịch vụ và dựa trên một tập hợp các nền tảng trung lập | 222 Goel Buyya Replication can be done either on the storage-array level or host level. In arraylevel replication data is copied from one disk array to another. Thus array-level replication is mostly homogeneous. The arrays are linked by a dedicated channel. Host-level replication is independent of the disk array used. Since arrays used in different hosts can be different host-level replication has to deal with heterogeneity. Host-level replication uses the TCP IP transmission-control protocol Internet protocol for data transfer. The replication in SAN also can be divided in two main categories based on the mode of replication a synchronous and b asynchronous as discussed earlier. Survey of Distributed Data-Storage Systems and Replication Strategies Used A brief explanation of systems in Table 3 follows. Arjuna Parrington et al. 1995 supports both active and passive replication. Passive replication is like primarycopy replication and all updates are redirected to the primary copy. The updates can be propagated after the transaction has committed. In active replication mutual consistency is maintained and the replicated object can be accessed at any site. Coda Kistler Satyanarayanan 1992 is a network-distributed file system. A group of servers can fulfill the client s read request. Updates are generally applied to all participating servers. Thus it uses a ROWA protocol. The motivation behind using this concept was to increase availability so that if one server fails other servers can take over and the request can be satisfied without the client s knowledge. The Deceit Siegel et al. 1990 distributed file system is implemented on top of the Isis Birman Joseph 1987 distributed system. It provides full network-filesystem NFS capability with concurrent read and writes. It uses write tokens and stability notification to control file replicas Siegel et al. . Deceit provides variable file semantics that offer a range of consistency guarantees from no consistency to .
