Disaster recovery in cloud computing: a survey <s> SecondSite <s> Errata: edited the Concurrent Write Detection Algorithm to match reality. Original paper: 18th September 2005, Proceedings of the 12th International Linux System Technology Conference. DRBD is a well established Linux software component to build HA (high availability) clusters out of common off-the-shelf hardware. DRBD’s key point is to replace shared storage systems by sharednothing networked mirroring. The most outstanding new feature is certainly our new "shared disk" mode, i.e. support for shareddisk file systems and other shared storage-aware applications. Provided that you use one of OpenGFS, GFS, OCFS2, this means that applications have read and write access to the mirrored data set on both nodes at the same time, since you can mount the storage on both peers simultanieously. Besides that, DRBD 8 supports effective resource level fencing. It prevents the divergence of the nodes’ copies of the data when DRBD’s communication path fails. Although DRBD has been widely used and under active development for 5 years now, it turned out that the method to determine the node with the up-to-date data was suboptimal. It was replaced by a new scheme based on UUIDs. This new scheme also works correctly in multi-node setups. <s> BIB001 </s> Disaster recovery in cloud computing: a survey <s> SecondSite <s> This paper describes the design and implementation of SecondSite, a cloud-based service for disaster tolerance. SecondSite extends the Remus virtualization-based high availability system by allowing groups of virtual machines to be replicated across data centers over wide-area Internet links. The goal of the system is to commodify the property of availability, exposing it as a simple tick box when configuring a new virtual machine. To achieve this in the wide area, we have had to tackle the related issues of replication traffic bandwidth, reliable failure detection across geographic regions and traffic redirection over a wide-area network without compromising on transparency and consistency. <s> BIB002
The SecondSite BIB002 ) is a disaster tolerance as a service system cloud. This platform is intended to cope three challenges: 1. Reducing RPO 2. Failure detection 3. Service restoration. For this reason, it uses three techniques:  Using a storage to keep writes between 2 checkpoints: Checkpoints move between sites in a specific period. However, if a failure happens in this time, some data will be lost. For this reason, a Distributed Replicated Block Device (DRBD) BIB001 ) is used to store replications in both synchronous and asynchronous modes.  Using a quorum node to detect and distinguish a real failure: A quorum node has been designed to monitor primary and backup server. If replications have not been received by the backup site in the waiting time, backup site sends a message to quorum node. In this case, if the quorum node receives a heartbeat form primary node, it means primary server is active and the replication link has a problem; otherwise the backup site will be active.  Using a backup site: There is a geographically separated backup site which allows to replicate groups of virtual machines through wide-area Internet links. SecondSite increases ability to fast failure detection and also differentiate between network failures and host failures. Using DRDB, resynchronize storage can be www.ccsenet.org/cis Computer and Information Science Vol. 7, No. 3; done for recovering primary site without VMs interruption in the backup site. Although, SecondSite is not suitable for stateless services, however it increases availability for small and medium businesses.