Examples of the present disclosure describe implementing bitmap-based data replication when a primary form of data replication between a source device and a target device cannot be used. According to one example, a temporal identifier may be received from the target device. If the source device determines that the primary replication method is unable to be used to replicate data associated with the temporal identifier, a secondary replication method may be initiated. The secondary replication method may utilize a recovery bitmap identifying data blocks that have changed on the source device since a previous event.

Storage redundancy may be resynchronized without determining a snapshot difference. A storage component (210) owning a volume (122) can maintain current and expected generation numbers (212, 214) based on modification requests received and modification requests that a backup component (220) acknowledges completing. The backup (220) can maintain current and expected generation numbers (222, 224) based on modification requests received and applied to a backup volume (124). If either component (210, 220) fails and later returns to service, differences between the owner's current and expected generation numbers (212, 214) and the backup's current and expected generation numbers (222, 224) indicate which modification requests may have been missed and need to be reconstructed to restore synchronization.

An apparatus in one embodiment comprises at least one processing device comprising a processor coupled to a memory, with the processing device being configured to detect a failure of at least one storage node that impacts a write cache destaging process in a distributed content addressable storage (CAS) system comprising a plurality of storage nodes each associated with one or more storage devices. Responsive to the detected failure, the processing device issues one or more write cache metadata preload commands to direct one or more other ones of the storage nodes to preload from their associated storage devices metadata characterizing one or more data pages that are subject to the write cache destaging process, thereby illustratively reducing address lock contention in the CAS system. The processing device illustratively comprises at least a portion of a distributed storage controller of the CAS system. Other embodiments include methods and computer program products.

Resilient mediation between storage systems replicating a dataset, including: receiving, by a mediation service from one or more storage systems that synchronously replicate a dataset, a request to resolve which storage system continues to service a dataset after the request; and sending, from the mediation service to at least one of the storage systems, a positive mediation result, wherein: the storage systems that received the positive mediation result continue to process data storage requests directed to the dataset, and the storage systems that did not receive a positive mediation result from the mediation service do not continue to process data storage requests directed to the dataset.

Synchronizing metadata among storage systems synchronously replicating a dataset, where synchronizing the metadata includes: receiving, at a first storage system of the storage systems, an I/O operation directed to the dataset; determining, in dependence upon the I/O operation, a metadata update describing a mapping of segments of content to a virtual address within a storage object, wherein the storage object includes the dataset; and synchronizing metadata on a second storage system of the storage systems by sending the metadata update to the second storage system to update a metadata representation on the second storage system in accordance with the metadata update.

A first server and a second server use a virtual address to mount the storage synchronous area in a storage by the NFS. The first server obtains a snapshot of memory content of a virtual system operated as an active system and transmits the snapshot to the second server. The first server replicates content of the storage synchronous area in the storage to a storage synchronous area in a storage. When a failure occurs in the first server, the second server sets a virtual address to the storage and uses the virtual address to mount the storage synchronous area in the storage by NFS. The second server uses the snapshot received from the first server to execute the application on the virtual system.

A method for synchronous replication of stream data includes receiving a stream of data blocks for storage at a first storage location associated with a first geographical region and at a second storage location associated with a second geographical region. The method also includes synchronously writing the stream of data blocks to the first storage location and to the second storage location. While synchronously writing the stream of data blocks, the method includes determining an unrecoverable failure at the second storage location. The method also includes determining a failure point in the writing of the stream of data blocks that demarcates data blocks that were successfully written and not successfully written to the second storage location. The method also includes synchronously writing, starting at the failure point, the stream of data blocks to the first storage location and to a third storage location associated with a third geographical region.

A system and method include reception, at a primary storage unit, of a first write request from a client including a first key and a first value, persisting of the first value in a first non-volatile memory of the primary storage unit in association with the first key, broadcast of the first write request and a first set of globally-durable keys to the one or more secondary storage units, reception, from each of the one or more secondary storage units, of an acknowledgement of the first write request and a first set of locally-durable keys, each of the first sets of locally-durable keys including the first key, reception, at the primary storage unit, of a second write request from the client including a second key and a second value, persisting of the second value in the first non-volatile memory in association with the second key, and broadcast of the second write request and a second set of globally-durable keys to the one or more secondary storage units, the second set of locally-durable keys including the first key.

A clustered pair of storage systems configured for active-active bidirectional synchronous replication expose a stretched volume over paths to both storage systems. Writes to the stretched volume received at each system are replicated to the peer system. The cluster can use a time-to-live (TTL) mechanism by which a non-preferred system continuously requests a TTL grant from the preferred system to remain in the cluster. Algorithms that reduce or avoid data unavailability are described and can include assessing the health of the systems in the cluster. An unhealthy system can trigger a one-sided polarization algorithm to notify the peer system that it is polarization winner. An improved polarization technique using a witness to decide the polarization winner includes a system adding a time delay before contacting the witness if the system is unhealthy. A control component can detect an unhealthy system and disable the active-active bidirectional synchronous replication.

One or more techniques and/or computing devices are provided for replicating virtual machine disk clones. For example, a first storage controller, hosting first storage, may have a synchronous replication relationship with a second storage controller hosting second storage. A virtual machine, within the first storage, may be specified as having synchronous replication protection. Accordingly, virtual machine disk clones of a virtual machine disk of the virtual machine may be replicated from the first storage to the second storage. For example, virtual machine disk clones may be synchronous replicated, replicated by a resync process invoked by a hypervisor agent, and/or stored and replicated from a clone backup directory.