Abstract: Techniques are provided for load balancing in a storage system using a storage system-driven host connectivity management process. For example, a load balancing process comprises monitoring a distribution of input/output (I/O) workload across resources of a storage system to detect for an occurrence of an I/O workload imbalance, generating updated connection information for a host system connected to the storage system, in response to detecting the occurrence of an I/O workload imbalance, and sending a request to the host system to discover the updated connection information for connecting to the storage system based on the updated connection information.

Abstract: Snapshots may be used to implement remote replication, for example, asynchronously, between a first storage system, A1, and a second storage system, A2. A1 may take a first snapshot, SS21, of a logical storage unit, R1. After the snapshot SS21 it taken, any dependent write operations associated with SS21 may be reconciled, and differences between SS21 and the last snapshot for R1, SS11, may be determined and recorded as a difference set. One or more replication instructions for R1 that include the write operations (or data and metadata corresponding thereto) of the difference set may be sent from A1 to A2. A2 may apply the differences to R2, and then take (activate) a snapshot of R2, SS22, which is a replica of SS21. After A2 activates SS22, A2 may send an acknowledgement to A1 indicating that SS22 has been activated, and A2 may take a next snapshot of R1.

Abstract: A first storage system receives a request to migrate a volume from the first storage system to a second storage system, and commences a migration process to non-disruptively migrate the volume from the first storage system to the second storage system while the volume is being accessed by a host system. The first storage system sends a first request to the host system to discover information for connecting to the second storage system to allow the host system to access to the volume through the second storage system during the migration process. In addition, the first storage system sends a second request to the host system to discover information for disconnecting from the first storage system during a final stage of the migration process.

Abstract: Techniques are provided for load balancing in a storage system using a storage system-driven host connectivity management process. For example, a load balancing process comprises monitoring a distribution of input/output (I/O) workload across resources of a storage system to detect for an occurrence of an I/O workload imbalance, generating updated connection information for a host system connected to the storage system, in response to detecting the occurrence of an I/O workload imbalance, and sending a request to the host system to discover the updated connection information for connecting to the storage system based on the updated connection information.

Abstract: Snapshots of a first logical storage unit (LSU) (R1) on a first storage system (A1) may be taken while replication is inactive between A1 and a second storage system (A2), such that these outstanding snapshots are not replicated to a second replica LSU (R2) on A2. Upon replication becoming active, the outstanding snapshots may be replicated to R2 without disrupting or impairing the remote replication of write operations between R1 and R2 as part of standard remote replication. A process on A1 executing the replication of the outstanding snapshots from R1 to R2 may be a separate process than one or more processes on A1 executing standard remote replication including the replication of write operations from R1 to R2. The process may be given low priority on A1 so as to not impair performance of other operations, including standard remote replication and replicating outstanding write operations on A1.

Abstract: Snapshots of a first logical storage unit (LSU) (R1) on a first storage system (A1) may be taken while replication is inactive between A1 and a second storage system (A2), such that these outstanding snapshots are not replicated to a second replica LSU (R2) on A2. Upon replication becoming active, the outstanding snapshots may be replicated to R2 without disrupting or impairing the remote replication of write operations between R1 and R2 as part of standard remote replication. A process on A1 executing the replication of the outstanding snapshots from R1 to R2 may be a separate process than one or more processes on A1 executing standard remote replication including the replication of write operations from R1 to R2. The process may be given low priority on A1 so as to not impair performance of other operations, including standard remote replication and replicating outstanding write operations on A1.

Abstract: Snapshots from a first LSU (R1) on a first storage system (A1) may be replicated to a second replica LSU (R2) on a second storage system (A2), for example, concurrently to remotely replicating (e.g., synchronously) write operations for R1 to R2. A process, P, on A1 executing the replication of the snapshots from R1 to R2 may be a separate process than the one or more processes on A1 executing remote replication of write operations for R1 to R2. During a consistency window on A1, outstanding write operations for R1 at the time the consistency window opened may be logged, and a pair of snapshots, SS11 and SS12 may be activated on R1 and R2, respectively. After the consistency window has closed, the SS12 snapshot metadata and snapshot data may be updated based on the outstanding write operations.

Abstract: Snapshots may be used to implement remote replication, for example, asynchronously, between a first storage system, A1, and a second storage system, A2. A1 may take a first snapshot, SS21, of a logical storage unit, R1. After the snapshot SS21 it taken, any dependent write operations associated with SS21 may be reconciled, and differences between SS21 and the last snapshot for R1, SS11, may be determined and recorded as a difference set. One or more replication instructions for R1 that include the write operations (or data and metadata corresponding thereto) of the difference set may be sent from A1 to A2. A2 may apply the differences to R2, and then take (activate) a snapshot of R2, SS22, which is a replica of SS21. After A2 activates SS22, A2 may send an acknowledgement to A1 indicating that SS22 has been activated, and A2 may take a next snapshot of R1.

Abstract: Maintaining consistency for asynchronous replication of LUNs of a local storage system to corresponding LUNs of a remote storage system includes copying application data written to LUNs to cache slots, copying metadata of LUNs to cache slots, associating a first sequence number to all metadata modifications and all application data writes that are begun after a first time and before a second time, associating a second sequence number, different from the first sequence number, to all metadata modifications and all application data writes that are begun after the second time, and, after completion of all metadata modifications and all application data writes associated with the first sequence number, initiating transfer to the remote storage system of all metadata modifications and all application data writes associated with the first sequence number. Each cache slot may include a field that indicates a corresponding sequence number.

Abstract: A technique for deploying virtual volumes in a metro cluster across first and second arrays includes impersonating a third array that purports to host single-site virtual volumes. The technique further includes mapping the single-site virtual volumes purportedly hosted by the third array to respective pairs of actual virtual volumes. Each pair includes a first virtual volume in the first array and a second virtual volume in the second array and realizes a stretched virtual volume, with writes being mirrored between the virtual volumes of each pair.

Abstract: A snapshot lookup table (SLT) and snapshot pointer structure(s) (SPSs) may be provided for a logical data unit (LSU), each SPS entry corresponding to an LSU data portion and a physical storage location at which data is stored for the data portion for a particular snapshot. A current lookup table (CLT) for a current time may be provided for an LSU, including an entry for each LSU data that points to a respective entry of an SPS. Each time a first write following the creation of a snapshot is made to an LSU data portion, the corresponding CLT entry may be updated to point to the SPS entry that was updated to point to an LSU track table entry. To create a snapshot, a snapshot lookup table (SLT) is created for each snapshot, and the contents of the CLT are copied to the newly created SLT.

Abstract: Maintaining consistency for asynchronous replication of LUNs of a local storage system to corresponding LUNs of a remote storage system includes copying application data written to LUNs to cache slots, copying metadata of LUNs to cache slots, associating a first sequence number to all metadata modifications and all application data writes that are begun after a first time and before a second time, associating a second sequence number, different from the first sequence number, to all metadata modifications and all application data writes that are begun after the second time, and, after completion of all metadata modifications and all application data writes associated with the first sequence number, initiating transfer to the remote storage system of all metadata modifications and all application data writes associated with the first sequence number. Each cache slot may include a field that indicates a corresponding sequence number.

Abstract: A no-copy clone of a logical storage unit is created. A define process is initiated for defining a target logical storage unit as the clone before activation of the target logical storage unit. By initiating the define process before activating the logical storage unit, there is a greater likelihood that, when a write operation is received for a data portion on the source logical storage unit or target logical storage unit after activation of the target LSU, the data portion will already be defined and not need to be defined when performing the write operation. When a write operation is received at the source logical storage unit, if the target logical storage unit is not active yet, the data of the write operation may be written to an allocated physical location for the data portion shared between the source and target logical storage units without updating any clone metadata.

Abstract: A snapshot lookup table (SLT) and snapshot pointer structure(s) (SPSs) may be provided for a logical data unit (LSU), each SPS entry corresponding to an LSU data portion and a physical storage location at which data is stored for the data portion for a particular snapshot. A current lookup table (CLT) for a current time may be provided for an LSU, including an entry for each LSU data that points to a respective entry of an SPS. Each time a first write following the creation of a snapshot is made to an LSU data portion, the corresponding CLT entry may be updated to point to the SPS entry that was updated to point to an LSU track table entry. To create a snapshot, a snapshot lookup table (SLT) is created for each snapshot, and the contents of the CLT are copied to the newly created SLT.

Abstract: A no-copy clone of a logical storage unit is created. A define process is initiated for defining a target logical storage unit as the clone before activation of the target logical storage unit. By initiating the define process before activating the logical storage unit, there is a greater likelihood that, when a write operation is received for a data portion on the source logical storage unit or target logical storage unit after activation of the target LSU, the data portion will already be defined and not need to be defined when performing the write operation. When a write operation is received at the source logical storage unit, if the target logical storage unit is not active yet, the data of the write operation may be written to an allocated physical location for the data portion shared between the source and target logical storage units without updating any clone metadata.

Abstract: An apparatus in one embodiment comprises at least one processing device having a processor coupled to a memory. The processing device is configured to maintain, for logical storage volumes of a storage system, device sequence numbers for snapshot and extent copy operations. The processing device is also configured to maintain, for at least one track of the logical storage volumes, a track sequence number representing the state of the track with respect to the snapshot and extent copy operations. The processing device is further configured to receive input/output operations directed to the logical storage volumes from host devices coupled to the storage system while at least one snapshot or extent copy operation for the logical storage volumes is in progress, and to utilize the track sequence numbers and the device sequence numbers to determine processing of the received input/output operations while the snapshot or extent copy operations are in progress.

Abstract: An apparatus in one embodiment comprises at least one processing device having a processor coupled to a memory. The processing device is configured to maintain, for logical storage volumes of a storage system, device sequence numbers for snapshot and extent copy operations. The processing device is also configured to maintain, for at least one track of the logical storage volumes, a track sequence number representing the state of the track with respect to the snapshot and extent copy operations. The processing device is further configured to receive input/output operations directed to the logical storage volumes from host devices coupled to the storage system while at least one snapshot or extent copy operation for the logical storage volumes is in progress, and to utilize the track sequence numbers and the device sequence numbers to determine processing of the received input/output operations while the snapshot or extent copy operations are in progress.

Abstract: Options for handling write operations may be selected based on a determined probability that a read operation for a portion of data will occur while the data portion is still in an I/O cache as a result of a write operation. As used herein, a “read-after-write event (“RAW”) is an occurrence of a read operation for a portion of data while the data portion is still in an I/O cache as a result of a write operation. The probability of a RAW may be determined by applying Bayesian inference, and may include applying exponential smoothing to calculations made on historical I/O information so that more recent I/O events have greater weight in determining RAW probability. Based on the determined RAW probability, write data may either be journaled in a write journal or written to a cache slot and de-staged to a physical storage device as part of write-in-place processing.

Abstract: Options for handling write operations may be selected based on a determined probability that a read operation for a portion of data will occur while the data portion is still in an I/O cache as a result of a write operation. As used herein, a “read-after-write event (”RAW?) is an occurrence of a read operation for a portion of data while the data portion is still in an I/O cache as a result of a write operation. The probability of a RAW may be determined by applying Bayesian inference, and may include applying exponential smoothing to calculations made on historical I/O information so that more recent I/O events have greater weight in determining RAW probability. Based on the determined RAW probability, write data may either be journaled in a write journal or written to a cache slot and de-staged to a physical storage device as part of write-in-place processing.

Abstract: Managing reservations for at least two different sites competing for a resource includes maintaining a table of groups of sites, where each group competes for the same resource, one of the different sites requesting a reservation for a particular resource, determining if the reservation is available by consulting the table, denying the reservation to the one of the at least two different sites in response to access having been previously reserved for an other one of the different sites, and granting the reservation to the one of the at least two different sites and reserving access for the one of the at least two different sites in response to the resource being available. The managed resources may correspond to data storage and the two different sites may be mirrored storage devices. In response to a failure of communication between the two different sites, pending writes may be failed.