Abstract: Efficient replication using assistance from a secondary node involves in one embodiment modifying data of a data volume at a primary node to create modified data. The primary node transmits the modified data to a first secondary node, wherein the first secondary node comprises a first replica of the data volume. The first secondary node receives and processes the modified data to generate processed data. The first secondary node transmits the processed data to the primary node. The primary node, in turn, receives and transmits the processed data to a second secondary node, wherein the second secondary node comprises a second replica of the data volume.

Abstract: Various systems and methods for maintaining write order fidelity in a distributed environment are disclosed. One method, which can be performed by each node in a cluster, involves associating a current sequence number with each of several write operations included in a set of independent write operations. In response to detecting that one of the write operations in the set is ready to complete, a new sequence number is selected, and that new sequence number is thereafter used as the current sequence number. None of write operations in the set is allowed to return to the application that initiated the write operations until the new sequence number has been advertised to each other node in the cluster. The method also involves receiving a message advertising a first sequence number from another node in the cluster, and subsequently using the first sequence number as the current sequence number.

Abstract: An apparatus and method implemented by a computer system of using data copies of a volume for redundancy when data of the volume is rendered corrupted or inaccessible. In one embodiment of the method a data volume is created. The data volume comprises a plurality of data blocks including a first data block. After creation of the data volume, a point-in-time (PIT) copy or a replica copy of the data volume is created, and a redirection map is created. The redirection map comprises a plurality of entries, wherein each entry of the map indicates whether memories allocated to store data of respective data blocks of the data volume and the PIT copy or the replica copy, contain identical data. Data of the data volume may become corrupt or inaccessible after creation of the PIT copy or replica copy.

Abstract: A method, system, and apparatus that provide an equivalent of persistent frozen image snapshots through the use of a time-addressable storage object, such as a time-indexed storage volume, are presented. These virtual snapshot images are presented to a system in a manner such that the image is not persistent and therefore (i) do not take up additional storage resources, and (ii) reduce the amount of volume management overhead that must be maintained since information about the snapshot can be discarded when the snapshot is no longer needed.

Abstract: A method, apparatus, and computer program product for setting and implementing a policy to compress the history of data on a temporal volume is described.

Abstract: One goal of consistency interval replication is to achieve a consistent copy of data generated by independent streams of writes from nodes in a clustered/distributed environment. Two writes to the same block from different nodes may arrive at a replication target in a different order from the order in which they were written to primary storage. A consistency interval coordinator may analyze a list of blocks modified during a consistency interval to determine conflict blocks written to by two different nodes during the same consistency interval. Conflict resolution may involve a node reading data for a conflict block from primary storage and forwarding it to the replication target or a node completing a suspended in-progress write for the conflict block. Once the conflicts have been resolved, the replication target may checkpoint the data modified during the interval and nodes may resume writes to the conflict blocks for the new interval.

Abstract: Various embodiments of systems and methods are disclosed for tracking valid regions of a working volume. State information identifies which regions of the working volume are currently valid. When the volume is created, the state information can be initialized to a value that identifies all regions of the volume as being invalid. The invalid regions do not need to be synchronized, since there will not be any need to reconstruct the data within those regions to a particular value. Accordingly, volume initialization, which synchronizes redundant data (e.g., RAID parity or a mirrored copy) with application data in the invalid regions, can be delayed. As the volume is accessed by an application, the redundant data associated with the regions being accessed is synchronized, and the state information is updated to indicate that those regions are valid.

Abstract: Methods, systems, and computer program products to provide temporal storage in a fabric-based virtualization environment are presented. Such capacity is provided through the association of a temporal storage appliance, which is configured as a member of a linked VLUN with a non-temporal disk volume. The linked VLUN is provided by a virtualizing fabric switch to a network node such as a network node.

Abstract: Systems and methods for performing snapshots in a storage environment employing distributed block virtualization. In one embodiment, the system may include a volume server, a first and a second host computer system, and a plurality of physical block devices. The volume server may be configured to aggregate storage in the plurality of physical block devices into a plurality of logical volumes, where a particular logical volume includes storage from at least two physical block devices. The volume server may further be configured to make a first and a second subset of the logical volumes available to the first and second host computer systems for input/output, respectively. The first subset and the second subset may be at least partially nonoverlapping, and a second logical volume may be configured to store a snapshot of data stored in a first logical volume logical volume.

Abstract: A system for multi-staged in-memory checkpoint replication with relaxed consistency includes a replication manager and a cluster with a plurality of nodes. In accordance with a configurable replication policy, the replication manager may be configured to identify a primary group of nodes to store primary replicas of a specified source memory region of a source node, and to identify a node of the primary group as an initiator of replication to a secondary group of nodes. In response to a replication request, the replication manager may be configured to copy contents of one or more data blocks of the source memory region to a each node of the primary group within a single atomic transaction, and initiate an operation to copy the contents of the data blocks from the initiator to an additional node of the secondary group.

Abstract: A method and system for mirror storage element resynchronization in a storage virtualization device is disclosed. According to one embodiment of the present invention, a read operation on a region of a data volume is received at a first module of a first storage virtualization device where the data volume is associated with at least a first mirror storage element and a second mirror storage element, a state indicated by a bit corresponding to the region of the data volume within a first synchronization map is determined in response to receiving the read operation, the read operation is processed using the first module if the bit is determined to indicate a first state and using a second module of the first storage virtualization device if the bit is determined to indicate a second state.

Abstract: Systems and methods are disclosed for performing cache and I/O management in a multi-layer storage virtualization environment. Block virtualization may be implemented at various layers, each with one or more storage entities. One storage entity may coordinate and leverage the cache and the caching mechanism available with another storage entity. The storage entities may be at the same layer (horizontal cache coordination) or at different layers (vertical cache coordination). Cache coordination may include application-assisted read-ahead.

Abstract: Disclosed is an apparatus or method performed by a computer system for creating a hierarchy of data volumes. Each data volume in the hierarchy is a point-in-time (PIT) copy of another data volume in the hierarchy or a PIT copy of a data volume V. In one embodiment of the apparatus or method, the contents of a first data volume in the hierarchy can be refreshed to the contents of a second data volume in the hierarchy such that the first data volume becomes a PIT copy of the second data volume. Before the first data volume is fully refreshed to the contents of the second data volume, data of the first data volume can be read or modified.

Abstract: Disclosed is a method and apparatus for optimizing memory space and improving the write performance in a data processing system having a data volume with multiple virtual copies thereof. In one embodiment of the method, a first virtual copy of a primary data volume is created. Thereafter, first data of the primary data volume is modified. A second virtual copy of the primary data volume is created after modification of the first data thereof. A write-data transaction for modifying second data of the modified primary data volume is generated after creation of the second virtual copy. The second data of the modified primary data volume is copied to memory allocated to store data of the second virtual copy. The second data of the modified primary data volume is modified after the second data is copied to the memory allocated to store data of the second virtual copy.

Abstract: Disclosed is a method and apparatus for refreshing a copy of a data volume. In one embodiment of the method first and second data portions of a data volume are copied to first and second memory blocks, respectively, of a memory coupled to a computer system. First and second bits of a first map stored in memory are then set, wherein the first and second bits correspond to the first and second memory blocks, respectively. The first data portion of the data volume is modified after the first data portion is copied to the first memory block. A first bit in a second map stored in memory is set after data of the first data portion is modified. An instruction is generated to refresh the data contents of the first and second memory blocks. The first bit of the first map is cleared in response to generation of the refresh instruction.

Abstract: Various embodiments of systems and methods are disclosed for initially synchronizing redundant data (e.g., a mirror, a replica, or a set of parity information) with an original volume. State information identifies which regions of the original volume are currently valid, and only valid regions of the original volume are used to generate the values of the redundant data during the initial synchronization. For example, if the redundant data is a set of parity information, synchronizing the redundant data involves calculating one or more parity values based on the valid regions of the volume. If the redundant data is a duplicate copy (e.g., a mirror or replica) of the volume, synchronizing the redundant data involves copying the valid regions of the volume to the duplicate copy of the volume. If the original volume includes any invalid regions, unnecessary copying and/or processing for those regions can be avoided during the initial synchronization.

Abstract: A virtual copy of data stored in a first memory is created in a second memory. Creating the virtual copy includes, in one embodiment, creating first and second tables in memory each one of which comprises a plurality of multibit entries. Each entry of the first table corresponds to a respective memory region of the first memory. Each entry of the second table corresponds to a respective memory region of the second memory. The first bit of the first and second tables indicates whether the corresponding memory region of the first and second memories, respectively, contains valid data. The second bit of the first and second tables indicates whether data in the corresponding memory region of the first and second memories, respectively, has been modified since the creation of the first and second tables, respectively.

Abstract: A method and system of providing periodic replication is disclosed. According to one embodiment, a method is provided which comprises creating a storage object corresponding to a storage volume, wherein the storage object comprises a point-in-time copy of the storage volume and a storage volume map; and replicating the storage volume using the storage object.

Abstract: A method or apparatus for cooperative data replication. The method in one embodiment can be performed by a computer system or several computer systems executing software instructions. The method may include modifying data in n data blocks of a data volume to create n modified data blocks. A copy of each of the n modified data blocks is created for subsequent transfer to other nodes. A first computer system transmits the n modified data block copies to n nodes, respectively, wherein each of the n nodes comprises a second computer system and a replica of the data volume prior to the modification of data in the n data blocks. Thereafter, one of the n second computer systems transmits a copy of the modified data block copy it receives to another of the n second computer systems.

Abstract: Disclosed is a method and apparatus for restoring a corrupted data volume. In one embodiment, the method includes creating a backup copy of the data volume before the data volume is corrupted. Data transactions that modify the contents of the data volume are stored in a transaction log. After detection of the data corruption, a virtual copy of the backup copy is created. Thereafter, select data transactions stored in the transaction log, are applied to the virtual copy. Data of the corrupted data volume is then overwritten with data of the backup copy and data of the virtual copy after applying data transactions to the virtual copy.