Abstract: A method for managing a cache memory of a storage system, the method may include receiving, by a controller of the storage system, an access request related to a data unit; wherein the receiving occurs while (a) the cache memory stores a group of oldest cached data units, and (b) the data unit is stored in a memory module of the storage system the differs from the cache memory; determining, by the controller, a caching category of the data unit; and preventing from caching the data unit in the cache memory when a hit score of the caching category of the data unit is lower than a hit score of the group of oldest cached data units; and caching the data unit in the cache memory when the hit score of the caching category of the data unit is higher than the hit score of the group of oldest cached data units; wherein the hit score of the caching category of the data unit is indicative of a probability of a cache hit per data unit of the caching category.

Abstract: A method for monitoring a storage system event, the method may include receiving, by a control unit of a storage system, a request to access a gauge that is associated with the storage system event; updating, by the control unit, a value of the gauge based on (a) a time difference between a time related to the request to access the gauge and a time related to a previous request to access the gauge, and (b) a length of a sliding time window; wherein when the request to access the gauge is triggered by an occurrence of an instance of the storage system event then the updating is further responsive to the occurrence of the instance of the storage system event; and wherein the value of the gauge provides an approximation of an average rate of instances of the storage system event during the sliding time window.

Abstract: A method for service level agreement allocation of permanent storage layer resources of a storage system, the method may include monitoring, by a control layer of the storage system, actual performances of the storage system that are related to multiple logical volumes; calculating actual-to-required relationships between the actual performances and service level agreement defined performances of the multiple logical volumes; allocating, for different logical volumes of the multiple logical volumes, allowable amounts of pending access requests; wherein the allocating is based on, at least, the actual-to-required relationships; receiving, by the control layer, received access requests aimed to one or more logical volumes of the logical volumes; and sending to the permanent storage layer requests to serve at least some of the received access requests, based on the allowable amounts of pending access requests.

Abstract: A method for disk error recovery management, the method may include (A) executing by a first control node, a first disk error recovery process that involves halting access, of the first control node, to a first group of storage devices. (B) Receiving by the first control node, during the execution of the disk error recovery process, a request to access a given storage device of the first group. (C) Directing the request to access the given storage device to a second control node if the second control node is not currently involved in an error recovery processes that involves halting access to the given storage device. (D) Accessing the given storage device by the second control node, during the execution of the disk error recovery process.

Abstract: A method for service level agreement (SLA) allocation of resources of a cache memory of a storage system, the method may include monitoring, by a control layer of the storage system, actual performances of the storage system that are related to multiple logical volumes; calculating actual-to-required relationships between the actual performances and SLA defined performances of the multiple logical volumes; assigning caching priorities, to different logical volumes of the multiple logical volumes; wherein the assigning is based on, at least, the actual-to-required relationships; and managing, based on at least the caching priorities, a pre-cache memory module that is upstream to the cache module and is configured to store write requests that (i) are associated with one or more logical volumes of the different logical volumes and (ii) are received by the pre-cache memory module at points in time when the cache memory is full; wherein the managing comprises transferring one or more write requests from the pre-ca

Abstract: A method for resolving conflicts related to states of multiple iSCSI sessions between an iSCSI initiator and an iSCSI target, the method may include: comparing between (a) iSCSI initiator information that is indicative of states of the multiple iSCSI sessions as viewed by the iSCSI initiator, and (b) iSCSI target information that is indicative of the states of the multiple iSCSI sessions as viewed by the iSCSI target; wherein the comparing is preceded by utilizing a non-iSCSI connection for gathering at least one of the iSCSI initiator information and the iSCSI target information; and participating in a resolution of a conflict related to a given iSCSI session out of the multiple iSCSI sessions when the comparing shows that a state of the given iSCSI session as indicated in the iSCSI initiator information conflicts with the state of the given iSCSI session as indicated in the iSCSI target information.

Abstract: A method for controlling compression based on compression ratio, the method includes monitoring access requests related to a storage entity of a storage system; wherein the access requests are associated with multiple data units; evaluating a compression ratio related to the storage entity; wherein the evaluating comprises applying a first compression process on at least a subset of the multiple data units to provide first compressed data units; serving the access requests without storing, in a permanent storage layer of the storage system, the first compressed data units; and reacting, by the storage system, to the compression ratio.

Abstract: A method for providing fast access, the method may include obtaining, by a first storage controller of a storage system, retrieval information for retrieving, from a permanent storage space, a subset of cached data units, the subset of the cached data units forms a part of a set of cached data units that are cached in a first cache memory and were destaged to the permanent storage space; and retrieving, using the retrieval information, at least some of the cached data units of the subset from the permanent storage space to a second cache memory, wherein the retrieving occurs in response to an occurrence of a failure to access the first cache memory; wherein the second cache memory differs from the first cache memory.

Abstract: A method for performing a comparison between first and second points in time snapshots of a file system entity, the method may include: (I) receiving by a storage system a command that was sent from a host computer, the command is network file system protocol compliant, wherein the command comprises (i) an operation code, and (ii) information about a virtual path, the virtual path that comprises (ii.a) first fields that comprise snapshot comparison parameters indicative of the first and second points in time snapshots of the file system entity, and (ii.

Abstract: A storage system, a computer program product and method for replicating a storage entity to a group of storage systems. The method may include splitting the storage entity, by a given storage system, to provide storage entity portions; generating, by the given storage system, storage entity portions information for distributing the storage entity portions between all storage systems of the group so that each storage system of the group eventually receives the storage entity portions; transmitting the storage entity portions, from the given storage system, to storage systems of the group; wherein the transmitting comprises transmitting different storage entity portions from the given storage system to different storage systems of the group; sending, by the given storage system, the storage entity portions information to at least some storage systems of the group; and attempting to verify, by the given storage system, that all the storage systems of the group received all the storage entity portions.

Abstract: A method for managing write requests in a storage system, the method may include receiving, by a receiving control node out of a group of control nodes of the storage system, a write request for writing a data unit to the storage system; storing the data unit in a first layer storage that is shared among the control nodes of the group, by the receiving control node; retrieving the data unit from the first layer storage and destaging the data unit to a second layer storage by a destaging control node that belongs to the group and is responsible for destaging the data unit; wherein at a time of the destaging of the data unit to the second layer storage another control node of the group is responsible for destaging another data unit to the second layer storage; wherein the storing of the data unit in the first layer storage is faster than the destaging of the data unit to the second layer storage; and when the destaging control node differs from the receiving control node then each one of the receiving and the s

Abstract: A method that may include receiving, by a storage system, a write request for storing in the storage system multiple input data units that are related to a certain file; comparing, by the storage system, the multiple input data units to stored data units of the certain file to find matching and non-matching input data units; wherein each matching input data unit equals a corresponding stored data unit and each non-matching input data unit differs from a corresponding stored data unit; preventing a storage of each matching input data unit; storing each non-matching input data unit; and updating at least one storage system management data structure to reflect a reception of non-matching input data units while not reflecting a reception of matching input data units.

Abstract: A method for synchronizing between a primary control node of a storage system and a secondary control node of the storage system, the method may include performing a change in a key-value store that is stored in shared memory of the storage system and includes control metadata for controlling access to data stored in the storage system; the shared memory is accessible to the primary control node and to a secondary control node; generating a change indication that (i) is indicative of the change in the key-value store and (ii) requests the secondary control node to introduce changes in one or more additional data structures that are not stored in the shared memory; the change in the key-value store comprises replacing a previous given value with a current given value that is associated with a given key; sending the change indication to the secondary control node; receiving an acknowledgement from the secondary control node; wherein the acknowledgement indicates at least one of the following: (i) the secondary

Abstract: A method for hash-based writing, the method comprises: receiving a received data entity to be stored in a storage system, wherein the received data entity is associated with received data entity metadata; selecting a selected data structure out of a set of data structures that comprises K data structures; wherein K is a positive integer; wherein for each value of a variable k that ranges between 2 and K, stored data entity metadata that is stored in a k'th data structure out of the set collided with stored data entity metadata that is stored in each one of a first till (k?1)'th data structures of the set; calculating an index by applying, on the received data entity metadata, a hash function that is associated with the selected data structure; determining whether an entry that is associated with the index and belongs to the selected data structure is empty; writing to the entry, if the entry is empty, the received data entity metadata, and storing the received data entity in the storage system in response to

Abstract: A method for de-duplication, the method may include receiving a request to store in a storage system a received data entity; obtaining a received data entity signature that is responsive to the received data entity; selecting a selected data structure out of a set of data structures that comprises K data structures; wherein K is a positive integer; wherein for each value of a variable k that ranges between 2 and K, a stored data entity signature that is stored in a k'th data structure out of the set collided with stored data entity signatures that are stored in each one of a first till (k?1)'th data structures of the set; calculating an index by applying, on the received data entity signature, a hash function that is associated with the selected data structure; determining whether an entry that is associated with the index and belongs to the selected data structure is empty; writing to the entry, if the entry is empty, the received data entity signature, and storing the received data entity in the storage sys

Abstract: A mass storage system obtains an hierarchical cluster mapping information; Host port state information, which is indicative of a state of at least one host port, is received from an intermediate device of a network that couples hosts to the mass storage system; The mass storage system estimates a state of an entity, which may be one or more host computers or a cluster of host computers. The estimating is based on the hierarchical cluster mapping information and the host port state information. The mass storage system determines whether to generate an alert, in response to the estimated state of the at least one entity. If it is determined to generate an alert then an alert is generated.

Abstract: A method that may include receiving, by a storage system, storage system configuration information that is indicative of access permissions of multiple host computer ports to storage logical units that are associated with a certain set of storage system ports; sending, by the storage system, in response to the storage system configuration information and to at least a first switch of a group of switches that is coupled to the storage system, access permission requests for allowing the multiple host computer ports to access the certain set of storage system ports; determining, by the storage system, to revoke an access permission from a certain host computer port of the multiple host computer hosts, when the certain host computer port failed to follow a predefined login pattern; and sending, by the storage system and to at least a second switch of the group of switches, a request to revoke the access permission of the certain host computer port.

Abstract: A method that may include determining, for each user of a group of users, a time difference between an event of a first type that is related to a storage of a user data unit of the user within a cache of a storage system and to an eviction of the user data unit from the cache, in response to (a) a service-level agreement (SLA) associated with the user and to (b) multiple data hit ratios associated with multiple different values of a time difference between events of the first type and evictions, from the cache, of multiple user data units of the user; and evicting from the cache, based upon the determination, one or more user data units associated with one or more users of the group.

Abstract: A method for writing data objects, the method may include accumulating, in a first memory module, multiple new data entities in one or more dirty pages of a data layer; wherein each new data entity and a corresponding older data entity are associated with a same application object; wherein the accumulating comprises storing each new data entity in a page that differs from a page that stores the corresponding older data entity; calculating multiple new sets of descriptors by generating to each new data entity, a new set of descriptors; wherein each set of descriptors comprises descriptors that belong to multiple descriptors layers; wherein the multiple descriptors layers and the data layer belong to an hierarchical data structure; accumulating the multiple new sets of descriptors in one or more dirty pages of one or more descriptors layers; wherein each corresponding older data entity is associated with a corresponding set of descriptors; wherein the accumulating comprises storing each new set of descriptor in

Abstract: A method that may include retrieving, by a decompression processor, a compressed data unit; wherein the compressed data unit comprises a control section and a data section; wherein the control section comprises multiple decompression instructions for a retrieval of data portions from one or more sources; wherein the one or more source comprise the data section; wherein the control section does not include any data portion; and executing, by a decompression processor, the multiple decompression instructions to provide a decompressed data unit.