Abstract: A method for managing a pool buffers includes establishing a first buffer class with a first allowable number of buffers, and a first reserved number of buffers that are reserved for the first buffer class in the pool of buffers even if no Input/Output (I/O) operation is running in connection with the first buffer class. The method includes establishing a second buffer class with a second allowable number of buffers, and a second reserved number of buffers that are reserved for the second buffer class in the pool of buffers even if no I/O operation is running in connection with the second buffer class. The first buffer is enabled class to have more than the first allowable number of buffers as long as a number of buffers allocated to the second buffer class is fewer than the second allowable number of buffers.

Abstract: A method for managing a pool buffers includes establishing a first buffer class with a first maximum allowable number of buffers, and a first reserved number of buffers that are reserved for the first buffer class in the pool of buffers even if no Input/Output (I/O) operation is running in connection with the first buffer class. The method includes establishing a second buffer class with a second maximum allowable number of buffers, and a second reserved number of buffers that are reserved for the second buffer class in the pool of buffers even if no I/O operation is running in connection with the second buffer class. The first buffer is enabled class to have more than the first maximum allowable number of buffers as long as a number of buffers allocated to the second buffer class is fewer than the second maximum allowable number of buffers.

Abstract: Embodiments herein provide for redundant data storage. One storage system includes first and second host systems each comprising a memory and a persistent storage device. The storage system also includes first and second storage controllers each comprising a memory (e.g., DRAM). The memory of the first storage controller is mapped to the memory of the first host system and the memory of the second storage controller is mapped to the memory of the second host system. The first storage controller is operable to DMA data from the persistent storage device of the first host system to the memory of the first storage controller, and to direct the second storage controller to DMA the data to the persistent storage device of the second host system via the memory of the second storage controller.

Abstract: An apparatus having a cache and a controller is disclosed. The controller is configured to (i) gather a plurality of statistics corresponding to a plurality of requests made from one or more hosts to access a memory during an interval, (ii) store data of the requests selectively in the cache in response to a plurality of headers and (iii) adjust one or more parameters in the headers in response to the statistics. The requests and the parameters are recorded in the headers.

Abstract: Methods and structure for selective cache mirroring. One embodiment includes a control unit and a memory. The memory is able to store indexing information for a multi-device cache for a logical volume. The control unit is able to receive an Input/Output (I/O) request from a host directed to a Logical Block Address (LBA) of the logical volume, to consult the indexing information to identify a cache line for storing the I/O request, and to store the I/O request at the cache line on a first device of the cache. The control unit is further able to mirror the I/O request to another device of the cache if the I/O request is a write request, and to complete the I/O request without mirroring the I/O request to another device of the cache if the I/O request is a read request.

Abstract: Systems and methods maintain cache coherency between storage controllers using input/output virtualization. In one embodiment, a primary storage controller receives write commands over a virtualized interface, stores the write commands in cache memory, tracks a status of the write commands processed from the cache memory, and stores the status in a portion of the cache memory. A backup storage controller includes a backup cache that receives replications of the write commands via direct memory access operations, and stores the replications of the write commands. The primary storage controller makes the status available to a host system. In response to a failure of the primary storage controller, the backup storage synchronizes with the status from the host system, and resumes I/O operations for the logical volume.

Abstract: Systems and methods to safely and efficiently handle dirty data flush are disclosed. More specifically, when a cache controller determines that one (or more) storage device of a cache device is running out of space, that storage device is given priority to be flushed prior to the other storage devices that are not in such a critical condition. In addition, a cache bypass process can be conditionally enabled to save free physical spaces already running low on such critical cache storage devices.

Abstract: Methods and structure for utilizing linked lists to flush a cache. One exemplary embodiment includes a memory, an interface, and an Input/Output (I/O) processor. The memory implements a cache divided into cache lines, and the interface receives I/O directed to a block address of a storage device. The I/O processor determines a remainder by dividing the block address by the number of cache lines, and selects a cache line for storing the I/O based on the remainder. The I/O processor determines a quotient by dividing the block address by the number of cache lines, and associates the quotient with the selected cache line. Additionally, the I/O processor populates a linked list by inserting entries that each point to a different cache line associated with the same quotient, and flushes the cache lines to the storage device in block address order by traversing the entries of the linked list.

Abstract: Embodiments herein provide for redundant data storage. One storage system includes first and second host systems each comprising a memory and a persistent storage device. The storage system also includes first and second storage controllers each comprising a memory (e.g., DRAM). The memory of the first storage controller is mapped to the memory of the first host system and the memory of the second storage controller is mapped to the memory of the second host system. The first storage controller is operable to DMA data from the persistent storage device of the first host system to the memory of the first storage controller, and to direct the second storage controller to DMA the data to the persistent storage device of the second host system via the memory of the second storage controller.

Abstract: Systems and methods maintain cache coherency between storage controllers using input/output virtualization. In one embodiment, a primary storage controller receives write commands over a virtualized interface, stores the write commands in cache memory, tracks a status of the write commands processed from the cache memory, and stores the status in a portion of the cache memory. A backup storage controller includes a backup cache that receives replications of the write commands via direct memory access operations, and stores the replications of the write commands. The primary storage controller makes the status available to a host system. In response to a failure of the primary storage controller, the backup storage synchronizes with the status from the host system, and resumes I/O operations for the logical volume.

Abstract: A storage subsystem can achieve more efficient I/O processing by enabling users to specify and pass out of band I/O hints comprising an object to be hinted, a hint type, and caching strategies associated with a hint type. A hinted object may be either a virtual device or a file. In addition to priority cache, hint types may include never-cache, sticky-cache, and volatile-cache. Hints may be passed via command-line or graphical-user interfaces.

Abstract: A system and method for managing the life expectancy of at least one solid state drive (SSD) within a cache device of a storage subsystem includes determining a baseline rate of decline for each SSD based on its guaranteed life expectancy. At intervals, each SSD of the cache device is polled for remaining life and power-on time, and a current rate of decline (based on time since initialization) and a cumulative rate of decline (based on total lifespan of the SSD) is determined. When both the current rate of decline and the cumulative rate of decline exceed the baseline rate of decline for any SSD of the cache device, write requests to that SSD are blocked and redirected to the virtual device until either the current rate of decline or cumulative rate of decline drop below the baseline rate.

Abstract: A system and method for managing cache memory of at least one node of a multiple-node storage cluster. A first cache data and a first cache metadata are stored for data transfers between a respective node and regions of a storage cluster receiving at least a first selected number of data transfer requests. When the node is rebooted, a second (new) cache data is stored to replace the first (old) cache data. The second cache data is compiled utilizing the first cache metadata to identify previously cached regions of the storage cluster receiving at least a second selected number of data transfer requests after the node is rebooted. The second selected number of data transfer requests is less than the first selected number of data transfer requests to enable a rapid build of the second cache data.

Abstract: The disclosure is directed to preserving data consistency in a multiple-node data storage system. According to various embodiments, a write log is maintained including log entries for data transfer requests being served by a respective node of the multiple-node data storage system. Rather than maintaining a full write journal of data and parity associated with each data transfer request, the log entries only need to identify portions of the virtual volume being updated according to the data transfer requests served by each node. When a first node fails, a second node takes over administration of a virtual volume for the failed node. Upon taking over for the first (failed) node, the second node resolves any inconsistencies between data and parity in portions of the virtual volume identified the respective log entries. Accordingly, write holes are prevented without substantially increasing memory usage or system complexity.

Abstract: A method generates input/output (IO) commands by plural different applications that execute on a host. The method prioritizes the applications by inserting different classifiers into the IO commands at a host bus adapter (HBA) located in the host. A storage device receives the IO commands and processes the IO commands according to priorities based on the classifiers for the applications.

Abstract: Methods and structure for selective cache mirroring. One embodiment includes a control unit and a memory. The memory is able to store indexing information for a multi-device cache for a logical volume. The control unit is able to receive an Input/Output (I/O) request from a host directed to a Logical Block Address (LBA) of the logical volume, to consult the indexing information to identify a cache line for storing the I/O request, and to store the I/O request at the cache line on a first device of the cache. The control unit is further able to mirror the I/O request to another device of the cache if the I/O request is a write request, and to complete the I/O request without mirroring the I/O request to another device of the cache if the I/O request is a read request.

Abstract: A cache controller having a cache supported by a non-volatile memory element manages metadata operations by defining a mathematical relationship between a cache line in a data store exposed to a host system and a location identifier associated with an instance of the cache line in the non-volatile memory. The cache controller maintains most recently used bit maps identifying data in the cache, as well as a data characteristic bit map identifying data that has changed since it was added to the cache. The cache controller maintains a most recently used bit map to replace the recently map at an appropriate time and a fresh bitmap tracks the most recently used bit map. The cache controller uses a collision bitmap, an imposter index and a quotient to modify cache lines stored in the non-volatile memory element.

Abstract: A method and system for IO processing in a storage system is disclosed. In accordance with the present disclosure, a controller may take long term “lease” of a portion (e.g., an LBA range) of a virtual disk of a RAID system and then utilize local locks for IOs directed to the leased portion. The method and system in accordance with the present disclosure eliminates inter-controller communication for the majority of IOs and improves the overall performance for a High Availability Active-Active DAS RAID system.

Abstract: A storage controller maintaining a cache manages modified data flush operations. A set-associative map or relationship between individual cache lines in the cache and a corresponding portion of the host managed or source data store is generated in such a way that a quotient can be used to identify modified data in the cache in the order of the source data's logical block addresses. The storage controller uses a collision bitmap, a dirty bit map and a flush table when flushing data from the cache. The storage controller selects a quotient and identifies modified cache lines in the cache identified by the quotient. As long as the quotient remains the same, the storage controller flushes or transfers the modified cache lines to the data store. Otherwise, when the quotient is not the same, the data in the cache is skipped. A linked list is used to traverse skipped cache lines.

Abstract: Systems and methods to safely and efficiently handle dirty data flush are disclosed. More specifically, when a cache controller determines that one (or more) storage device of a cache device is running out of space, that storage device is given priority to be flushed prior to the other storage devices that are not in such a critical condition. In addition, a cache bypass process can be conditionally enabled to save free physical spaces already running low on such critical cache storage devices.