Patent Publication Number: US-2022229786-A1

Title: Retrieval of portions of storage device access data indicating access state changes

Description:
FIELD 
     The field relates generally to information processing systems, and more particularly to storage in information processing systems. 
     BACKGROUND 
     Storage arrays and other types of storage systems are often shared by multiple host devices over a network. Applications running on the host devices each include one or more processes that perform the application functionality. The processes issue input-output (TO) operations for delivery to storage ports of the storage system. The storage ports are typically limited in number and each has limited resources for handling IO operations received from the host devices. Different ones of the host devices can run different applications with varying workloads and associated IO patterns. Such host devices also generate additional IO operations in performing various data services such as replication and migration so as to meet business continuity requirements. 
     Host device multi-pathing arrangements may use different protocols to access storage systems and/or obtain information about the storage systems and paths to the storage systems. One such protocol is NVMe (Non-Volatile Memory Express) protocol. For example, Asymmetric Namespace Access (ANA) is an NVMe standard implemented to enable host devices to obtain information about accessing a given namespace of a storage array. 
     SUMMARY 
     Illustrative embodiments configure a host device to include functionality for retrieving portions of storage device access data from a storage array. For example, some embodiments include techniques for enabling a host device to request those portions of storage device access data indicating namespace state changes. 
     In one embodiment, an apparatus comprises at least one processing device that is configured to control delivery of IO operations from a host device to a storage system over selected ones of a plurality of paths through a network. The at least one processing device is further configured to send one or more requests to the storage system for data corresponding to states of a plurality of storage devices in the storage system. The one or more requests comprise a directive that the data corresponding to the states returned by the storage system relate to changes in the states of the plurality of storage devices. The at least one processing device is also configured to receive the data corresponding to the states from the storage system, to identify one or more state changes of one or more of the plurality of storage devices based on the received data, and to manage one or more of the IO operations responsive to the identified one or more state changes. 
     These and other illustrative embodiments include, without limitation, apparatus, systems, methods and computer program products comprising processor-readable storage media. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an information processing system configured with functionality in a multi-path layer of a host device for retrieving and analyzing portions of storage device access data indicating state changes in an illustrative embodiment. 
         FIG. 2  is a flow diagram of a process for retrieving and analyzing portions of storage device access data indicating state changes in an illustrative embodiment. 
         FIG. 3  is a block diagram showing multiple layers of a layered system architecture that includes a multi-path layer with functionality for retrieving and analyzing portions of storage device access data indicating state changes in an illustrative embodiment. 
         FIG. 4  is a block diagram showing ANA groups of a storage array in an illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Illustrative embodiments will be described herein with reference to exemplary information processing systems and associated computers, servers, storage devices and other processing devices. It is to be appreciated, however, that embodiments of the present disclosure are not restricted to use with the particular illustrative system and device configurations shown. Accordingly, the term “information processing system” as used herein is intended to be broadly construed, so as to encompass, for example, processing systems comprising cloud computing and storage systems, as well as other types of processing systems comprising various combinations of physical and virtual processing resources. An information processing system may therefore comprise, for example, at least one data center that includes one or more clouds hosting multiple tenants that share cloud resources. Numerous other types of enterprise and cloud-based computing and storage systems are also encompassed by the term “information processing system” as that term is broadly used herein. 
       FIG. 1  shows an information processing system  100  configured in accordance with an illustrative embodiment. The information processing system  100  comprises a plurality of host devices  102 - 1 ,  102 - 2 , . . .  102 -N. The host devices  102  communicate over a storage area network (SAN)  104  with at least one storage array  105 . The storage array  105  comprises a plurality of storage devices  106 - 1 , . . .  106 -M each storing data utilized by one or more applications running on one or more of the host devices  102 . The storage devices  106  are illustratively arranged in one or more storage pools. The storage array  105  and its associated storage devices  106  are an example of what is more generally referred to herein as a “storage system.” This storage system in the present embodiment is shared by the host devices  102 , and is therefore also referred to herein as a “shared storage system.” Other embodiments can include only a single host device, possibly configured to have exclusive use of the storage system. 
     The host devices  102  illustratively comprise respective computers, servers or other types of processing devices capable of communicating with the storage array  105  of the SAN  104 . For example, at least a subset of the host devices  102  may be implemented as respective virtual machines of a compute services platform or other type of processing platform. The host devices  102  in such an arrangement illustratively provide compute services such as execution of one or more applications on behalf of each of one or more users associated with respective ones of the host devices  102 . 
     The term “user” herein is intended to be broadly construed so as to encompass numerous arrangements of human, hardware, software or firmware entities, as well as combinations of such entities. 
     Compute and/or storage services may be provided for users under a Platform-as-a-Service (PaaS) model, an Infrastructure-as-a-Service (IaaS) model and/or a Function-as-a-Service (FaaS) model, although it is to be appreciated that numerous other cloud infrastructure arrangements could be used. Also, illustrative embodiments can be implemented outside of the cloud infrastructure context, as in the case of a stand-alone computing and storage system implemented within a given enterprise. 
     The storage devices  106  of the storage array  105  of SAN  104  implement LUNs or namespaces configured to store objects for users associated with the host devices  102 . These objects can comprise files, blocks or other types of objects. LUNs are implemented in connection with Small Computer System Interface (SCSI) protocol and namespaces are implemented in connection with NVMe protocol. 
     As used herein, the term “namespace” is intended to be broadly construed so as to encompass, for example, a collection of logical block addresses (LBA) accessible to host software. A namespace can correspond to the isolation of logical blocks addressable by the host software. 
     As used herein, a “namespace ID (NSID)” is intended to be broadly construed so as to encompass, for example, an identifier used by a storage controller to provide access to a namespace. In Linux, for example, namespaces each appear with a unique identifier in devices (e.g., /dev/nvme0n1 refers to controller 0 and namespace 1). 
     As used herein, the term “server” is to be broadly construed, and may encompass a host device, such as, for example, host device  102 - 1 , a portion of a host device or a processing device separate from a host device. 
     The host devices  102  interact with the storage array  105  utilizing read and write commands as well as other types of commands, such as, for example, SCSI commands like log select and log sense commands, or NVMe commands like the Get Log Page command, described further herein, that are transmitted over the SAN  104 . A given IO operation as that term is broadly used herein illustratively comprises one or more such commands. References herein to terms such as “input-output”and “TO” should be understood to refer to input and/or output. Thus, an TO operation relates to at least one of input and output. 
     Example embodiments refer to NVMe commands, although other types of commands can be used in other embodiments. Some embodiments can implement TO operations utilizing command features and functionality associated with NVMe protocol, as described in the NVMe Specification, Revision 1.4a, March 2020, which is incorporated by reference herein. Other storage protocols of this type that may be utilized in illustrative embodiments disclosed herein include NVMe over Fabric, also referred to as NVMeoF. 
     The term “storage device” as used herein is intended to be broadly construed, so as to encompass, for example, a logical storage device such as a namespace, LUN or other logical storage volume. A logical storage device can be defined in the storage array  105  to include different portions of one or more physical storage devices. Storage devices  106  may therefore be viewed as comprising respective namespaces, LUNs or other logical storage volumes. 
     Each of the host devices  102  illustratively has multiple paths to the storage array  105 , with at least one of the storage devices  106  of the storage array  105  being visible to that host device on a given one of the paths. A given one of the storage devices  106  may be accessible to the given host device over multiple paths. 
     Different ones of the storage devices  106  of the storage array  105  illustratively exhibit different latencies in processing of TO operations. In some cases, the same storage device may exhibit different latencies for different ones of multiple paths over which that storage device can be accessed from a given one of the host devices  102 . 
     The host devices  102 , SAN  104  and storage array  105  in the  FIG. 1  embodiment are assumed to be implemented using at least one processing platform each comprising one or more processing devices each having a processor coupled to a memory. Such processing devices can illustratively include particular arrangements of compute, storage and network resources. For example, processing devices in some embodiments are implemented at least in part utilizing virtual resources such as virtual machines (VMs) or Linux containers (LXCs), or combinations of both as in an arrangement in which Docker containers or other types of LXCs are configured to run on VMs. 
     The host devices  102  and the storage array  105  may be implemented on respective distinct processing platforms, although numerous other arrangements are possible. For example, in some embodiments at least portions of the host devices  102  and the storage array  105  are implemented on the same processing platform. The storage array  105  can therefore be implemented at least in part within at least one processing platform that implements at least a subset of the host devices  102 . 
     The SAN  104  may be implemented using multiple networks of different types to interconnect storage system components. For example, the SAN  104  may comprise a portion of a global computer network such as the Internet, although other types of networks can be part of the SAN  104 , including a wide area network (WAN), a local area network (LAN), a satellite network, a telephone or cable network, a cellular network, a wireless network such as a WiFi or WiMAX network, or various portions or combinations of these and other types of networks. The SAN  104  in some embodiments therefore comprises combinations of multiple different types of networks each comprising processing devices configured to communicate using Internet Protocol (IP) or other related communication protocols. 
     As a more particular example, some embodiments may utilize one or more high-speed local networks in which associated processing devices communicate with one another utilizing Peripheral Component Interconnect express (PCIe) cards of those devices, and networking protocols such as InfiniBand, Gigabit Ethernet or Fibre Channel. Numerous alternative networking arrangements are possible in a given embodiment, as will be appreciated by those skilled in the art. 
     The host devices  102  comprise respective sets of IO queues  110 - 1 ,  110 - 2 , . . .  110 -N and respective MPIO drivers  112 - 1 ,  112 - 2 , . . .  112 -N. The MPIO drivers  112  collectively comprise a multi-path layer of the host devices  102 . The multi-path layer provides functionality for retrieving and analyzing portions of storage device access data indicating state changes. Such functionality is provided at least in part using respective instances of path selection logic  114 - 1 ,  114 - 2 , . . .  114 -N, and respective instances of access state request generation and analysis logic  116 - 1 ,  116 - 2 , . . .  116 -N implemented within the MPIO drivers  112 . 
     The MPIO drivers  112  may comprise, for example, otherwise conventional MPIO drivers, such as PowerPath® drivers from Dell Technologies, suitably modified in the manner disclosed herein to provide functionality for retrieving and analyzing portions of storage device access data indicating state changes. Other types of MPIO drivers from other driver vendors may be suitably modified to incorporate functionality for retrieving and analyzing portions of storage device access data indicating state changes as disclosed herein. 
     The MPIO driver  112 - 1  is configured to deliver IO operations selected from its corresponding set of IO queues  110 - 1  to the storage array  105  via selected ones of multiple paths over the SAN  104 . The sources of the IO operations stored in the set of IO queues  110 - 1  illustratively include respective processes of one or more applications executing on the host device  102 - 1 . For example, IO operations can be generated by each of multiple processes of a database application running on the host device  102 - 1 . Such processes issue IO operations for delivery to the storage array  105  over the SAN  104 . Other types of sources of IO operations may be present in a given implementation of system  100 . 
     The paths from the host device  102 - 1  to the storage array  105  illustratively comprise paths associated with respective initiator-target pairs, with each initiator comprising a host bus adaptor (HBA) or other initiating entity of the host device  102 - 1  and each target comprising a port or other targeted entity corresponding to one or more of the storage devices  106  of the storage array  105 . As noted above, the storage devices  106  illustratively comprise namespaces, LUNs or other types of logical storage devices. 
     In some embodiments, the paths are associated with respective communication links between the host device  102 - 1  and the storage array  105  with each such communication link having a negotiated link speed. For example, in conjunction with registration of a given HBA to a switch of the SAN  104 , the HBA and the switch may negotiate a link speed. The actual link speed that can be achieved in practice in some cases is less than the negotiated link speed, which is a theoretical maximum value. 
     Various scheduling algorithms, load balancing algorithms and/or other types of algorithms can be utilized by the MPIO driver  112 - 1  in delivering IO operations from the IO queues  110 - 1  to the storage array  105  over particular paths via the SAN  104 . Each such IO operation is assumed to comprise one or more commands for instructing the storage array  105  to perform particular types of storage-related functions such as reading data from or writing data to particular logical volumes of the storage array  105 , or other types of functions, such as log sense commands to send requests to the storage array  105  for data corresponding to performance of one or more switch fabrics in the SAN  104 . Such commands are assumed to have various payload sizes associated therewith, and the payload associated with a given command is referred to herein as its “command payload.” 
     A command directed by the host device  102 - 1  to the storage array  105  is considered an “outstanding” command until such time as its execution is completed in the viewpoint of the host device  102 - 1 , at which time it is considered a “completed” command. The commands illustratively comprise respective NVMe or SCSI commands, although other command formats can be used in other embodiments. A given such command is illustratively defined by a corresponding command descriptor block (CDB) or similar format construct. The given command can have multiple blocks of payload associated therewith, such as a particular number of 512-byte SCSI blocks or other types of blocks. 
     In illustrative embodiments to be described below, it is assumed without limitation that the initiators of a plurality of initiator-target pairs comprise respective HBAs of the host device  102 - 1  and that the targets of the plurality of initiator-target pairs comprise respective ports of the storage array  105 . Examples of such HBAs and storage array ports are illustrated in conjunction with the embodiment of  FIG. 3 . 
     Selecting a particular one of multiple available paths for delivery of a selected one of the IO operations of the set of IO queues  110 - 1  is more generally referred to herein as “path selection.” Path selection as that term is broadly used herein can in some cases involve both selection of a particular IO operation and selection of one of multiple possible paths for accessing a corresponding logical device of the storage array  105 . The corresponding logical device illustratively comprises a namespace, LUN or other logical storage volume to which the particular IO operation is directed. 
     It should be noted that paths may be added or deleted between the host devices  102  and the storage array  105  in the system  100 . For example, the addition of one or more new paths from host device  102 - 1  to the storage array  105  or the deletion of one or more existing paths from the host device  102 - 1  to the storage array  105  may result from respective addition or deletion of at least a portion of the storage devices  106  of the storage array  105 . 
     Addition or deletion of paths can also occur as a result of zoning and masking changes or other types of storage system reconfigurations performed by a storage administrator or other user. 
     Some embodiments are configured to send a predetermined command from the host device  102 - 1  to the storage array  105 , illustratively utilizing the MPIO driver  112 - 1 , to determine if zoning and masking information has been changed. The predetermined command can comprise, for example, log select and log sense commands as described herein, a mode sense command, a “vendor unique command” or VU command, or combinations of multiple instances of these or other commands, in an otherwise standardized command format. 
     In some embodiments, paths are added or deleted in conjunction with addition of a new storage array or deletion of an existing storage array from a storage system that includes multiple storage arrays, possibly in conjunction with configuration of the storage system for at least one of a migration operation and a replication operation. 
     For example, a storage system may include first and second storage arrays, with data being migrated from the first storage array to the second storage array prior to removing the first storage array from the storage system. 
     As another example, a storage system may include a production storage array and a recovery storage array, with data being replicated from the production storage array to the recovery storage array so as to be available for data recovery in the event of a failure involving the production storage array. 
     In these and other situations, path discovery scans may be repeated as needed in order to discover the addition of new paths or the deletion of existing paths. 
     A given path discovery scan can be performed utilizing known functionality of conventional MPIO drivers, such as PowerPath® drivers. 
     The path discovery scan in some embodiments may be further configured to identify one or more new namespaces, LUNs or other logical storage volumes associated with the one or more new paths identified in the path discovery scan. The path discovery scan may comprise, for example, one or more bus scans which are configured to discover the appearance of any new namespaces or LUNs that have been added to the storage array  105  as well to discover the disappearance of any existing namespaces, LUNs that have been deleted from the storage array  105 . 
     The MPIO driver  112 - 1  in some embodiments comprises a user-space portion and a kernel-space portion. The kernel-space portion of the MPIO driver  112 - 1  may be configured to detect one or more path changes of the type mentioned above, and to instruct the user-space portion of the MPIO driver  112 - 1  to run a path discovery scan responsive to the detected path changes. Other divisions of functionality between the user-space portion and the kernel-space portion of the MPIO driver  112 - 1  are possible. 
     For each of one or more new paths identified in the path discovery scan, the host device  102 - 1  may be configured to execute a host registration operation for that path. The host registration operation for a given new path illustratively provides notification to the storage array  105  that the host device  102 - 1  has discovered the new path. 
     As is apparent from the foregoing, MPIO driver  112 - 1  of host device  102 - 1  is configured to control delivery of IO operations from the host device  102 - 1  to the storage array  105  over selected paths through the SAN  104 . 
     The MPIO driver  112 - 1  is further configured with access state request generation and analysis logic  116 - 1  to parse responses to requests for storage device access states received from the storage array  105 . For example, as noted herein, ANA is an NVMe standard implemented to enable host devices to obtain information about accessing a given namespace of a storage array. Asymmetric storage controller behavior occurs in NVMe subsystems where namespace access characteristics (e.g., performance) may vary based on, for example, the internal configuration of an NVMe subsystem and/or which storage controller (e.g., one of the storage controllers  120 ) is used to access a namespace. NVMe subsystems that provide asymmetric controller behavior may support ANA reporting. NVMe subsystems supporting ANA reporting divide namespaces into a number of ANA groups, each ANA group containing one or more namespaces. Namespaces that are members of the same ANA group perform identical ANA state transitions. In one or more embodiments, the ANA group maintains the same asymmetric namespace access state for all namespaces that are members of that ANA group. Referring to  FIG. 4 , an example storage array  405  comprises a plurality of ANA groups, ANA group 1  450 - 1 , ANA group 2  450 - 2 , . . . ANA group L  450 -L (collectively “ANA groups  450 ”). Each ANA group  450  comprises a plurality of namespaces (namespace 1, namespace 2, . . . namespace K)  451 - 1 ,  451 - 2 , . . .  451 -L (collectively “namespaces  451 ”). The number of ANA groups  450  and the number of namespaces  451  in each ANA group can vary, and is implementation dependent. For example, some storage arrays use only one ANA group for all of the namespaces of a storage controller, while other storage arrays have one ANA group for each namespace corresponding to a storage controller. 
     In illustrative embodiments, a storage array  105  (or  405 ) reports ANA states for volumes in response to NVMe Get Log Page commands from a host device  102 - 1  to the storage array  105 . In order to receive and read ANA state changes for each volume, the host device  102 - 1 , and more particularly, the access state request generation and analysis logic  116 - 1 , sends Get Log Page commands to the storage array  105 . Using the storage controller  120  and the access state notification logic  122 , the storage array  105  responds to the Get Log Page command with different ANA states of given namespaces of the storage array  105 . The host device  102 - 1 , and more particularly, the access state request generation and analysis logic  116 - 1 , analyzes a response to a Get Log Page command received from the storage array  105  and, along with the path selection logic  114 - 1  applies the identified ANA states when selecting the paths to the volume. 
     According to an illustrative embodiment, in a response to a host device request for access state information, a response by the storage array (e.g., storage array  105  or  405 ) identifies ANA groups (e.g., ANA groups  450 ) by respective ANA group IDs in respective ANA group descriptors for each of the ANA groups. Each ANA group descriptor includes NSIDs for the namespaces (e.g., namespaces  451 ) associated with a given ANA group ID. 
     With conventional techniques, host device parsing of a Get Log Page command output from a storage array is complex and consumes relatively large amounts of time. Host device software requires multiple computation cycles to parse Get Log Page command outputs, making it difficult for host device multi-pathing software to control IO operations, especially when IO operations fail during non-disruptive upgrades and migrations. 
     In illustrative embodiments the access state request generation and analysis logic  116 - 1  requests, and the access state notification logic  122  responds with, an ANA log page that provides only changed ANA descriptors instead of providing each ANA descriptor whether the ANA descriptor has been changed or not changed. Advantageously, according to the embodiments, an ANA state request by the access state request generation and analysis logic  116 - 1  specifies that access state data returned by a storage system only relate to ANA state changes. In response to such a request, the access state notification logic  122  replies to the host device  102 - 1  with a log page that omits ANA descriptors that have not changed, and includes just the modified ANA descriptors. As a result, the access state request generation and analysis logic  116 - 1  and the path selection logic  114 - 1  can read and apply ANA state changes quickly to affected namespaces without the parsing overhead of conventional techniques. Additional examples of retrieving and analyzing portions of storage device access data indicating state changes are described herein in conjunction with the embodiments of  FIGS. 1 through 4 . 
     In the  FIG. 1  embodiment, the storage array  105  comprises a plurality of storage controllers  120  and one or more instances of access state notification logic  122 . A more detailed example of the access state notification logic  122  will be described herein in conjunction with the embodiments of  FIGS. 1 through 4 . Additional components not explicitly shown in the figure, such as one or more storage caches, may also be provided in the storage array  105  for use in processing IO operations. For example, in some embodiments, each of the storage controllers  120  has a different local cache or a different allocated portion of a global cache associated therewith, although numerous alternative arrangements are possible. The storage controllers  120  can be implemented as respective storage processors, directors or other storage system components configured to control storage system operations relating to processing of IO operations. 
     When an IO operation sent on a path fails, in order to determine whether failure is due to an ANA state change, the access state request generation and analysis logic  116 - 1  generates and transmits to the storage array  105  a Get Log Page command that requests only changed ANA descriptors instead of each ANA descriptor whether the ANA descriptor has been changed or not changed. In response to the Get Log Page command having the requirement that only changed ANA descriptors be included in the returned log page, the access state notification logic  122  generates a log page that includes the changed ANA descriptors, and omits any ANA descriptors that have not changed since a previous invocation. The host device  102 - 1  receives the ANA log from the storage array  105 , the access state request generation and analysis logic  116 - 1  parses the contents of the ANA log, and the path selection logic  114 - 1  applies the ANA state changes as needed and sends the IO operations to the most suitable paths. 
     Under conventional techniques, where a Get Log Page command does not include a requirement that only changed ANA descriptors be included in the returned log page, the storage array would return a log buffer comprising all ANA descriptors whether or not the ANA descriptors changed since a previous invocation, requiring the host device to parse a much larger response log than a response log generated according to the techniques of the embodiments. During parsing of the larger response log, which takes much longer than parsing of the response log generated in accordance with the disclosed embodiments, IO operations are held by the host to determine the appropriate path. The delay in sending the IO operations during the time to parse the content of the larger ANA log page leads to performance degradation. 
     In a non-limiting illustrative example, in the case of a given storage array where each ANA group descriptor corresponds to only one namespace, if a storage controller has 4096 namespaces, there will be 4096 ANA group descriptors respectively corresponding to the 4096 namespaces. In this case, the size of an ANA log including the 4096 ANA group descriptors will be approximately 145 KB. If there are 4 storage controllers, a host device will be required to obtain and parse a 145 KB ANA log for each controller. Absent the techniques of the embodiments, in this example, each time a host device reads an ANA log, a host device is required to analyze all of the 4096 ANA group descriptors in order to identify affected namespaces and apply state changes. Under conventional techniques, since there may be thousands of namespaces for each storage controller, parsing entire contents of an ANA log to determine ANA state is time consuming and inefficient. 
     Illustrative embodiments provide techniques for requesting and obtaining an ANA log page which provides changed group descriptors only. As a result, a host device  102 - 1  is able to parse returned log pages and apply state changes much more quickly and efficiently than with conventional techniques. According to the embodiments, during booting or initialization of a host device  102 - 1 , the access state request generation and analysis logic  116 - 1  reads and parses an entire ANA log and records a change count of the ANA log page and/or each ANA group descriptor. When there is a change to the ANA log, using the storage controller  120  and the access state notification logic  122 , the storage array  105  sends an ANA notification to the host device  102 - 1 . Responsive to the ANA notification, the host device  102 - 1 , more particularly, the access state request generation and analysis logic  116 - 1 , generates and sends a Get Log Page request specifying that only the changed ANA log descriptors be transmitted to the host device  102 - 1  in a response log page. The storage array  105 , more particularly, the access state notification logic  122 , returns to the host device  102 - 1  a log page including only changed group descriptors and omitting unmodified group descriptors. The access state request generation and analysis logic  116 - 1  reads and parses the information corresponding to the changed group descriptors in the response log and the path selection logic  114 - 1  applies the ANA state changes in the selection of paths for TO operations as required. The host device  102 - 1  further records an updated change count of the ANA log page and/or each group descriptor from the previous invocation. 
     For example, the host device  102 - 1  sends one or more requests to the storage array  105  for data corresponding to states (e.g., ANA states) of a plurality of storage devices  106 . As per the access state request generation and analysis logic  116 - 1 , the one or more requests comprise a directive that the data corresponding to the states returned by the storage array  105  relate to changes in the states of the plurality of storage devices  106 . The host device  102 - 1  receives the data corresponding to the states from the storage array  105 , identifies one or more state changes of one or more of the plurality of storage devices  106  based on the received data, and manages one or more TO operations responsive to the identified one or more state changes. The directive in the request that the data corresponding to the states returned by the storage array  105  relate to state changes may comprise, for example, a VU command or other type of command occupying a dedicated number of bits of a Get Log Page command. As used herein, the term “directive” is intended to be broadly construed so as to encompass, for example, a command, an instruction or other information specifying one or more characteristics of the data to be returned. 
     According to an embodiment, the plurality of storage devices  106  are divided into a plurality of groups (e.g., ANA groups), and comprise a plurality of storage volumes, wherein respective ones of the plurality of storage volumes correspond to a namespace associated with a NSID. The data corresponding to the states received from the storage array  105  comprises at least one ANA group descriptor for at least one ANA group of a plurality of ANA groups. The at least one ANA group descriptor indicates a change in data from a previous instance of the least one ANA group descriptor. The data corresponding to the states omits one or more ANA group descriptors not indicating a change in data from previous instances of the one or more ANA group descriptors. 
     In one or more embodiments, the host device  102 - 1  maintains a count of changes in data associated with respective ones of a plurality of ANA group descriptors, and increments the count for different instances of the respective ones of the plurality of ANA group descriptors received by the storage system in response to different ones of the one or more requests. The host device  102 - 1  stores change counts in one or more storage buffers, caches and/or databases of the host device  102 - 1 . 
     A state change comprises, for example, removal of a storage device, replacement of a storage device with a new storage device, an addition of a new storage device and/or an ANA state change. A response buffer may specify ANA states for namespaces as, for example, optimized, non-optimized, inaccessible, changed or in a persistent loss state. For example, an ANA group descriptor can include a field for ANA state, indicating the ANA state for all namespaces in an ANA group when accessed through a controller. 
     In illustrative embodiments, the host device  102 - 1  learns the ANA state of the namespaces through ANA Get Log Page commands that request only changed ANA descriptors instead of each ANA descriptor whether the ANA descriptor has been changed or not changed. A Get Log Page command may be generated in response to an asynchronous event notification received from a storage array  105  or by polling a storage controller  120 . An asynchronous event may include, for example, an ANA state change to one or more group descriptors, an addition or deletion NSIDs to one or more group descriptors, and/or an NSID of a namespace being moved from one ANA group descriptor to a different ANA group descriptor. In addition, there are different use cases where an NVMe subsystem may invoke ANA state change event, such as, for example, non-disruptive storage array firmware upgrades and migrations. 
     An ANA log includes a header describing the log and group descriptors comprising ANA information for ANA groups that contain namespaces that are attached to the controller processing the command. According to an embodiment, each ANA group descriptor comprises a series of bytes indicating, for example, an ANA group identifier (ANA group ID), which identifies the ANA group that is the subject of the descriptor, the number of NSID values in the group descriptor and the NSIDs for each of the namespaces in the group. ANA group descriptors are provided in an ANA log in ascending ANA group identifier order. In accordance with the embodiments, a response ANA log will include the ANA group descriptors corresponding to changes and the number of changes. In keeping with the operational example of 4096 group descriptors, if there are only 2 group descriptors with changes, the response buffer will include those 2 group descriptors and not the other 4094 group descriptors. 
     The ANA log includes two types of “change count” fields. The first type is a change count for the ANA log. This field contains a 64-bit incrementing ANA log change count, indicating an identifier for this set of ANA information. The count starts at 0 h following a controller level reset and is incremented each time the contents of the log page change. The second type is a change count for the ANA group descriptor. This field contains a 64-bit incrementing count, indicating an identifier for the information contained in this ANA group descriptor. If a change count is reported, then the count starts at 1 h following a controller level reset and is incremented each time the data in this ANA group descriptor changes. The host device  102 - 1  can use the two types of change count fields to determine changes since a last invocation. 
     Offsets of ANA group descriptors with an ANA log and its size are variable depending upon a number of namespaces in each ANA group. As noted herein, the number of ANA groups and namespaces in each group is implementation dependent. 
     As noted herein, the host device  102 - 1  transmits requests for storage device access information to the storage array  105 . In some embodiments, such requests are transmitted to the storage array utilizing one or more NVMe protocol commands, such as, for example, the Get Log Page command as described herein, which are processed by the storage controller  120  and the access state notification logic  122  to provide a response with the access state information to the host device  102 - 1 . The embodiments are not necessarily limited to the use of NVMe protocol commands, and may also be utilized with other protocols, and their associated commands. 
     As noted herein, information can be obtained by the host device  102 - 1  from the storage array  105 , or information can be obtained by the storage array  105  from the host device  102 - 1  utilizing an in-band communication mechanism in which one or more predetermined commands in a designated storage protocol are sent from the host device  102 - 1  to the storage array  105  or vice versa. Such predetermined commands can comprise, for example, a Get Log Page command, log sense and log select commands, a mode sense command, a VU command, or combinations of multiple instances of these or other commands, in an otherwise standardized command format, such as NVMe format, or another type of format. 
     Additionally or alternatively, information can be obtained by the host device  102 - 1  from the storage array  105 , or information can be obtained by the storage array  105  from the host device  102 - 1  utilizing an out-of-band communication mechanism. For example, an out-of-band communication mechanism of this type can involve host management software of the host device  102 - 1  communicating with storage array management software of the storage array  105  over an IP network connection or other type of network connection. 
     These and other functions related to retrieving and analyzing portions of storage device access data indicating state changes that are referred to herein as being performed by or under the control of the MPIO driver  112 - 1  can in some embodiments be performed at least in part outside of the MPIO driver  112 - 1 , such as in the host device  102 - 1  generally. 
     References herein to an MPIO driver such as MPIO driver  112 - 1  being configured to retrieve and analyze portions of storage device access data indicating state changes are intended to be broadly construed, and should not be viewed as being limited to any particular storage arrangement, such as storage in a particular host device component or using a particular format. Accordingly, such storage can be in a memory or other storage device that is outside of the MPIO driver. 
     Illustrative embodiments provide for optimal handling of access state (e.g., ANA state) buffer data by host devices. Host device multi-pathing software works in tandem with storage array tasks such as, for example, volume migrations or array non-disruptive upgrades. In such storage array tasks, access states (e.g., NVMe ANA states) are being transitioned from one state to another state by the storage arrays, which expect host software to act in accordance with the changed ANA states. Hosts corresponding to multiple storage volumes (e.g., namespaces) are required to quickly consume state changes with respect to their configurations and data structures in order to successfully process IO operations. 
     Advantageously, in an illustrative embodiment, the access state request generation and analysis logic  116 - 1  of the MPIO driver  112 - 1  allows the host device  102 - 1  to request and receive only ANA descriptors and NSIDs pertaining to state changes, requiring less time to parse through response logs from a storage array  105  and apply changes. The embodiments provide optimal methods of handling ANA state changes regardless of whether there are one or multiple NSIDs for each ANA group descriptor. With conventional techniques, even if an ANA state is changed for only one namespace, host device software must parse entire ANA log contents for each controller, identify affected namespaces and apply state changes. Unlike current approaches, only modified namespaces and group descriptors will be returned by the storage array, resulting in less time to identify and apply state changes. 
     The above-described functions associated with retrieving and analyzing portions of storage device access data indicating state changes in the MPIO driver  112 - 1  are carried out at least in part under the control of its path selection logic  114 - 1  and/or access state request generation and analysis logic  116 - 1 . For example, the path selection logic  114 - 1  and/or access state request generation and analysis logic  116 - 1  are illustratively configured to control performance of an algorithm comprising the steps of the flow diagram to be described below in conjunction with  FIG. 2 . In other embodiments, one or more such steps can be more generally performed by the host device  102 - 1 . 
     It is assumed that each of the other MPIO drivers  112  is configured in a manner similar to that described above and elsewhere herein for the first MPIO driver  112 - 1 . The other host devices  102  of the system  100  are therefore also configured to communicate over the SAN  104  with the storage array  105 . The MPIO drivers  112  of such other host devices are each similarly configured to deliver IO operations from its corresponding one of the sets of IO queues  110  to the storage array  105  over selected paths through the SAN  104 , and to perform the disclosed functionality for retrieving and analyzing portions of storage device access data indicating state changes. 
     Accordingly, functionality described above in the context of the first MPIO driver  112 - 1  and the first host device  102 - 1  is assumed to be similarly performed by each of the other MPIO drivers  112 - 2  through  112 -N and/or more generally by their respective host devices  102 - 2  through  102 -N. 
     The MPIO drivers  112  may be otherwise configured utilizing well-known MPIO functionality such as that described in “Dell EMC SC Series Storage and Microsoft Multipath I/O,” Dell EMC, CML 1004, July 2018, which is incorporated by reference herein. Such conventional MPIO functionality is suitably modified in illustrative embodiments disclosed herein to support retrieving and analyzing portions of storage device access data indicating state changes. 
     The storage array  105  in the present embodiment is assumed to comprise a persistent memory that is implemented using a flash memory or other type of non-volatile memory of the storage array  105 . More particular examples include NAND-based flash memory or other types of non-volatile memory such as resistive RAM, phase change memory, spin torque transfer magneto-resistive RAM (STT-MRAM) and Intel Optane™ devices based on 3D XPoint™ memory. The persistent memory is further assumed to be separate from the storage devices  106  of the storage array  105 , although in other embodiments the persistent memory may be implemented as a designated portion or portions of one or more of the storage devices  106 . For example, in some embodiments the storage devices  106  may comprise flash-based storage devices, as in embodiments involving all-flash storage arrays, or may be implemented in whole or in part using other types of non-volatile memory. 
     As mentioned above, communications between the host devices  102  and the storage array  105  may utilize PCIe connections or other types of connections implemented over one or more networks. For example, illustrative embodiments can use interfaces such as Internet SCSI (iSCSI), Serial Attached SCSI (SAS) and Serial ATA (SATA). Numerous other interfaces and associated communication protocols can be used in other embodiments. 
     The storage array  105  in some embodiments may be implemented as part of cloud infrastructure in the form of a cloud-based system such as an Amazon Web Services (AWS) system. Other examples of cloud-based systems that can be used to provide at least portions of the storage array  105  and possibly other portions of system  100  include Google Cloud Platform (GCP) and Microsoft Azure. 
     The storage devices  106  of the storage arrays  105  can be implemented using solid state drives (SSDs). Such SSDs are implemented using non-volatile memory (NVM) devices such as flash memory. Other types of NVM devices that can be used to implement at least a portion of the storage devices  106  include non-volatile random access memory (NVRAM), phase-change RAM (PC-RAM) and magnetic RAM (MRAM). These and various combinations of multiple different types of NVM devices or other storage devices may also be used. For example, hard disk drives (HDDs) can be used in combination with or in place of SSDs or other types of NVM devices. Accordingly, numerous other types of electronic or magnetic media can be used in implementing at least a subset of the storage devices  106 . 
     The storage array  105  may additionally or alternatively be configured to implement multiple distinct storage tiers of a multi-tier storage system. By way of example, a given multi-tier storage system may comprise a fast tier or performance tier implemented using flash storage devices or other types of SSDs, and a capacity tier implemented using HDDs, possibly with one or more such tiers being server based. A wide variety of other types of storage devices and multi-tier storage systems can be used in other embodiments, as will be apparent to those skilled in the art. The particular storage devices used in a given storage tier may be varied depending on the particular needs of a given embodiment, and multiple distinct storage device types may be used within a single storage tier. As indicated previously, the term “storage device” as used herein is intended to be broadly construed, and so may encompass, for example, SSDs, HDDs, flash drives, hybrid drives or other types of storage products and devices, or portions thereof, and illustratively include logical storage devices such as LUNs and namespaces. 
     As another example, the storage array  105  may be used to implement one or more storage nodes in a cluster storage system comprising a plurality of storage nodes interconnected by one or more networks. 
     It should therefore be apparent that the term “storage array” as used herein is intended to be broadly construed, and may encompass multiple distinct instances of a commercially-available storage array. For example, the storage array  105  may comprise one or more storage arrays such as one or more VNX®, VMAX®, Unity™ or PowerMax™ storage arrays, commercially available from Dell Technologies. 
     Other types of storage products that can be used in implementing a given storage system in illustrative embodiments include software-defined storage, cloud storage, object-based storage and scale-out storage. Combinations of multiple ones of these and other storage types can also be used in implementing a given storage system in an illustrative embodiment. 
     In some embodiments, a storage system comprises first and second storage arrays arranged in an active-active configuration. For example, such an arrangement can be used to ensure that data stored in one of the storage arrays is replicated to the other one of the storage arrays utilizing a synchronous replication process. Such data replication across the multiple storage arrays can be used to facilitate failure recovery in the system  100 . One of the storage arrays may therefore operate as a production storage array relative to the other storage array which operates as a backup or recovery storage array. 
     It is to be appreciated, however, that embodiments disclosed herein are not limited to active-active configurations or any other particular storage system arrangements. Accordingly, illustrative embodiments herein can be configured using a wide variety of arrangements, including, by way of example, active-passive arrangements, active-active Asymmetric Logical Unit Access (ALUA) arrangements, other types of ALUA arrangements and the ANA arrangements as detailed herein. 
     These and other storage systems can be part of what is more generally referred to herein as a processing platform comprising one or more processing devices each comprising a processor coupled to a memory. A given such processing device may correspond to one or more virtual machines or other types of virtualization infrastructure such as Docker containers or other types of LXCs. As indicated above, communications between such elements of system  100  may take place over one or more networks. 
     The term “processing platform” as used herein is intended to be broadly construed so as to encompass, by way of illustration and without limitation, multiple sets of processing devices and one or more associated storage systems that are configured to communicate over one or more networks. For example, distributed implementations of the host devices  102  are possible, in which certain ones of the host devices  102  reside in one data center in a first geographic location while other ones of the host devices  102  reside in one or more other data centers in one or more other geographic locations that are potentially remote from the first geographic location. Thus, it is possible in some implementations of the system  100  for different ones of the host devices  102  to reside in different data centers than the storage array  105 . 
     Numerous other distributed implementations of the host devices  102  and/or the storage array  105  are possible. Accordingly, the storage array  105  can also be implemented in a distributed manner across multiple data centers. 
     It is to be appreciated that these and other features of illustrative embodiments are presented by way of example only, and should not be construed as limiting in any way. Accordingly, different numbers, types and arrangements of system components such as host devices  102 , SAN  104 , storage array  105 , storage devices  106 , sets of IO queues  110 , MPIO drivers  112  and instances of path selection logic  114  and access state request generation and analysis logic  116  can be used in other embodiments. 
     It should also be understood that the particular sets of modules and other components implemented in the system  100  as illustrated in  FIG. 1  are presented by way of example only. In other embodiments, only subsets of these components, or additional or alternative sets of components, may be used, and such components may exhibit alternative functionality and configurations. 
     The operation of the information processing system  100  will now be described in further detail with reference to the flow diagram of the illustrative embodiment of  FIG. 2 . The process as shown includes steps  200  through  206 , and is suitable for use in the system  100  but is more generally applicable to other types of systems comprising at least one host device and a storage system. The storage system in this embodiment is assumed to comprise at least one storage array having a plurality of storage devices. The storage devices can include logical storage devices such as namespaces, LUNs or other logical storage volumes. 
     The steps of the  FIG. 2  process are illustratively performed at least in part by or under the control of an MPIO driver of a given host device. For example, portions of the process may be carried out under the control of software, firmware and/or hardware of an instance of path selection logic deployed within the MPIO driver. Accordingly, the  FIG. 2  process may be viewed as an example of an algorithm performed by the path selection logic  114 - 1  and/or access state request generation and analysis logic  116 - 1  of the MPIO driver  112 - 1  of host device  102 - 1 . Other arrangements of host device components and/or other system components can be configured to perform at least portions of one or more of the steps in other embodiments. 
     In step  200 , one or more requests are sent to a storage system for data corresponding to states of a plurality of storage devices in the storage system. The one or more requests comprise a directive that the data corresponding to the states returned by the storage system relate to changes in the states of the plurality of storage devices. In one or more embodiments, the plurality of storage devices are divided into a plurality of groups comprising respective ones of a plurality of ANA groups. The plurality of storage devices may comprise a plurality of storage volumes, respective ones of the plurality of storage volumes corresponding to a namespace associated with a NSID. 
     In step  202 , the data corresponding to the states from the storage system is received, and in step  204 , one or more state changes of one or more of the plurality of storage devices are identified based on the received data. In step  206 , one or more IO operations over a plurality of paths are managed responsive to the identified one or more state changes. 
     The data corresponding to the states from the storage system comprises one or more ANA group descriptors for one or more ANA groups of the plurality of ANA groups. Responsive to the directive that the data corresponding to the states returned by the storage system relate to changes in the states of the plurality of storage devices, the one or more ANA group descriptors indicate a change in data associated with the one or more ANA group descriptors from previous instances of the one or more ANA group descriptors. Further responsive to the directive that the data corresponding to the states returned by the storage system relate to state changes, the data corresponding to the states from the storage system omits ANA group descriptors not indicating a change in data from their previous instances. 
     The host device  102 - 1  maintains a count of changes in data associated with respective ones of the plurality of ANA group descriptors, and increments the count for different instances of the respective ones of the plurality of ANA group descriptors received by the storage system in response to different ones of the one or more requests. 
     Multiple additional instances of the  FIG. 2  process may be performed in respective additional host devices that share the storage array. Other embodiments can include multiple storage arrays, with the disclosed functionality for retrieving and analyzing portions of storage device access data indicating state changes being implemented for each of those storage arrays. 
     The particular processing operations and other system functionality described in conjunction with the flow diagram of  FIG. 2  are presented by way of illustrative example only, and should not be construed as limiting the scope of the disclosure in any way. Alternative embodiments can use other types of processing operations involving host devices, storage systems and functionality for retrieving and analyzing portions of storage device access data indicating state changes. For example, the ordering of the process steps may be varied in other embodiments, or certain steps may be performed at least in part concurrently with one another rather than serially. Also, one or more of the process steps may be repeated periodically, or multiple instances of the process can be performed in parallel with one another in order to implement the disclosed functionality for retrieving and analyzing portions of storage device access data indicating state changes within a given information processing system. 
     Functionality such as that described in conjunction with the flow diagram of  FIG. 2  can be implemented at least in part in the form of one or more software programs stored in memory and executed by a processor of a processing device such as a computer or server. As will be described below, a memory or other storage device having executable program code of one or more software programs embodied therein is an example of what is more generally referred to herein as a “processor-readable storage medium.” 
     Referring now to  FIG. 3 , another illustrative embodiment is shown. In this embodiment, an information processing system  300  comprises one or more instances of path selection logic  314 , access state request generation and analysis logic  316  and access state notification logic  321 . The system  300  is configured in accordance with a layered system architecture that illustratively includes a host device processor layer  330 , an MPIO layer  332 , an HBA layer  334 , a switch fabric layer  336 , a storage array port layer  338  and a storage array processor layer  340 . The host device processor layer  330 , the MPIO layer  332  and the HBA layer  334  are associated with one or more host devices, the switch fabric layer  336  is associated with one or more SANs or other types of networks, and the storage array port layer  338  and storage array processor layer  340  are associated with one or more storage arrays (“SAs”). 
     The system  300  in this embodiment implements retrieving and analyzing portions of storage device access data indicating state changes as characterized by access state request generation and analysis logic  316 . The access state request generation and analysis logic  316  is illustratively shown as part of the MPIO layer  332 . Alternatively, the access state request generation and analysis logic  316  in other embodiments is illustratively stored, at least partially, in the host device processor layer  330 . It is also possible in some embodiments that the access state request generation and analysis logic  316  can be incorporated within a data structure of the path selection logic  314 . The access state request generation and analysis logic  316  (or  116 ) illustratively requests from the storage array processor layer  340 , ANA log pages that provide only changed ANA descriptors instead of providing each ANA descriptor whether the ANA descriptor has been changed or not changed. Advantageously, according to the embodiments, a request for state data by the access state request generation and analysis logic  316  specifies that access state data returned by a storage system only relate to changed states. In response to such a request, the access state notification logic  321  replies to a host device with a log page that omits ANA descriptors that have not changed, and includes just the modified ANA descriptors. As a result, the access state request generation and analysis logic  316  and the path selection logic  314  can read and apply ANA state changes quickly to affected namespaces without the parsing overhead of conventional techniques. 
     In order to determine access state changes (e.g., ANA state changes), which affect path selection for IO operations by the path selection logic  314  of the MPIO layer  332 , the host device via, for example, the host device processor or MIPO layers  330  and  332 , periodically requests access state data buffers, using for example, a Get Log Page command including a command therein that specifies that only changed ANA group descriptors be returned. For each response (e.g., log page) processed and sent by, for example, the access state notification logic  321  of the storage array processor layer  340 , and received by a host device, the access state request generation and analysis logic  316  analyzes the ANA group descriptors included in the log page to identify storage volumes (e.g., namespaces) where there is a state change. Based on this analysis, the access state request generation and analysis logic  316  determines the state changes (e.g., ANA state changes) of identified storage volumes. The access state request generation and analysis logic  316 , along with the path selection logic  314  manages IO operations over selected ones of the plurality of paths responsive to the identified changes in storage volume access states. 
     According to an embodiment, the storage array processor layer  340  receives requests for access state information from a host device, and processes and responds to such requests using the access state notification logic  321  (or  122 ). For example, the access state notification logic  321  receives and responds to Get Log Page commands received from a host device with a log page including ANA group IDs, ANA group descriptors and NSIDs along with any state changes of the associated storage volumes (e.g., namespaces). As noted herein, the access state notification logic  321  returns only modified ANA group descriptors in a log page in response to a request indicating that only data corresponding to state changes be returned. When there is a change to ANA states, the access state notification logic  321  sends an ANA notification to the host device processor and/or MPIO layer  300  or  332 . The access state notification logic  321  is implemented in the storage array processor layer  340  and can include functionality for the system  300  the same or similar to that described in connection with the access state notification logic  122 . It is also possible in some embodiments that the access state notification logic  321  can include multiple logic instances for respective ones of a plurality of storage arrays of the system  300 . 
     The MPIO layer  332  is an example of what is also referred to herein as a multi-path layer, and comprises one or more MPIO drivers implemented in respective host devices. Each such MPIO driver illustratively comprises an instance of path selection logic  314  and access state request generation and analysis logic  316  configured to implement functionality for retrieving and analyzing portions of storage device access data indicating state changes substantially as previously described. Additional or alternative layers and path selection and/or access state request generation and analysis logic arrangements can be used in other embodiments. 
     In the system  300 , path selection logic  314  is configured to select different paths for sending IO operations and/or commands from a given host device to a storage array. These paths as illustrated in the figure include a first path from a particular HBA denoted HBA 1  through a particular switch fabric denoted SF 1  to a particular storage array port denoted PORT 1 , and a second path from another particular HBA denoted HBA 2  through another particular switch fabric denoted SF 2  to another particular storage array port denoted PORT 2 . 
     These two particular paths are shown by way of illustrative example only, and in many practical implementations there will typically be a much larger number of paths between the one or more host devices and the one or more storage arrays, depending upon the specific system configuration and its deployed numbers of HBAs, switch fabrics and storage array ports. For example, each host device in the  FIG. 3  embodiment can illustratively have a set of n paths to a shared storage array, or alternatively different ones of the host devices can have different numbers and types of paths to the storage array. 
     The path selection logic  314  of the MPIO layer  332  in this embodiment therefore selects paths for delivery of IO operations and/or commands to the one or more storage arrays having the storage array ports of the storage array port layer  338 . In selecting the paths, the path selection logic  314  illustratively limits amounts of IO operations and/or commands that are delivered over one or more paths to particular ones of the ports of a storage array. 
     It is assumed in this embodiment that the host devices through their respective MPIO drivers and respective instances of path selection logic  314  and access state request generation and analysis logic  316  provide functionality for retrieving and analyzing portions of storage device access data indicating state changes, possibly with involvement of other host device components. 
     Accordingly, in some embodiments, the path selection logic  314  utilizes the access state request generation and analysis logic  316  in determining appropriate paths over which to send particular IO operations and/or commands to ports of one or more storage arrays. As described elsewhere herein, such receiving and processing of storage device access data can substantially improve system performance. 
     Some implementations of the system  300  can include a relatively large number of host devices (e.g., 1000 or more host devices), although as indicated previously different numbers of host devices, and possibly only a single host device, may be present in other embodiments. Each of the host devices is typically allocated with a sufficient number of HBAs to accommodate predicted performance needs. In some cases, the number of HBAs per host device is on the order of 4, 8 or 16 HBAs, although other numbers of HBAs could be allocated to each host device depending upon the predicted performance needs. A typical storage array may include on the order of 128 ports, although again other numbers can be used based on the particular needs of the implementation. The number of host devices per storage array port in some cases can be on the order of 10 host devices per port. The HBAs of the host devices are assumed to be zoned and masked to the storage array ports in accordance with the predicted performance needs, including user load predictions. 
     A given host device of system  300  can be configured to initiate an automated path discovery process to discover new paths responsive to updated zoning and masking or other types of storage system reconfigurations performed by a storage administrator or other user. For certain types of host devices, such as host devices using particular operating systems such as Windows, ESX or Linux, automated path discovery via the MPIO drivers of a multi-path layer is typically supported. Other types of host devices using other operating systems such as AIX in some implementations do not necessarily support such automated path discovery, in which case alternative techniques can be used to discover paths. 
     The particular features and functionality of the illustrative embodiments described above can be varied in other embodiments. 
     Also, as mentioned previously, different instances of the above-described algorithms and other storage device access data receiving and processing techniques can be performed by different MPIO drivers in different host devices. 
     The particular storage device access data receiving and processing arrangements described above are therefore presented by way of illustrative example only. Numerous alternative arrangements of these and other features can be used in implementing the storage device access data receiving and processing functionality in other illustrative embodiments. 
     The illustrative embodiments disclosed herein can provide a number of significant advantages relative to conventional arrangements that fail to provide efficient techniques for analyzing whether storage volumes associated with given groups in a response buffer are subject to state changes. Advantageously, the embodiments configure a multi-path layer of one or more host devices to include functionality for retrieving and analyzing portions of storage device access data indicating state changes, leading to enhanced overall performance. For example, using access state request generation and analysis logic, a multi-path layer advantageously requests and receives an ANA log page that provides only changed ANA descriptors instead of each ANA descriptor whether the ANA descriptor has been changed or not changed. By only receiving modified ANA descriptors, the embodiments eliminate the need to parse through entire response buffers including data for every group descriptor to determine whether there have been changes to storage volumes for each group. 
     Using current approaches, host device parsing of a Get Log Page command output is complex and consumes relatively large amounts of time since response buffers include data for ANA groups where there have been no state changes. Even when there is a small number of ANA groups where state changes have occurred, conventional techniques require parsing through data associated with every ANA group in order to determine whether and where changes may have occurred. Accordingly, with current approaches, host device software requires multiple computation cycles to parse Get Log Page command outputs, making it difficult for host device multi-pathing software to control IO operations, especially when IO operations fail during non-disruptive upgrades and migrations. 
     With the techniques of the embodiments, the host devices generate and send a Get Log Page command that requests only changed ANA log descriptors so that a storage array processing the command returns only changed group descriptors to the host device. As a result, the host device reads and parses only information corresponding to changed group descriptors, which results in faster turnaround time to apply state changes to multipathing decisions. 
     These and other illustrative embodiments provide significant advantages over conventional practice. For example, such embodiments are much more efficient and effective than conventional multipathing solutions that require parsing of larger portions of data before recognizing ANA state changes. Unlike former approaches, according to the embodiments, parsing time is reduced considerably by reducing the size of a response buffer by limiting its content to data for groups where changes have occurred, resulting in increased IO operation performance. 
     Illustrative embodiments provide techniques for host devices to request and receive only changed ANA descriptors and the corresponding NSIDs, requiring less time to parse through response logs from a storage array and apply changes. Advantageously, such pinpointed data in a response buffer enables host device software to conclude correct ANA states much more quickly, and avoids parsing through data where there were no ANA state changes. The embodiments therefore provide for efficient and timely multi-pathing decisions to be made in cases where ANA states are often transitioning during storage array tasks like volume-migration, array non-disruptive upgrades and other such case(s) where ANA state changes occur. 
     It is to be appreciated that the particular advantages described above are associated with particular illustrative embodiments and need not be present in other embodiments. Also, the particular types of information processing system features and functionality as illustrated in the drawings and described above are exemplary only, and numerous other arrangements may be used in other embodiments. 
     It was noted above that portions of an information processing system as disclosed herein may be implemented using one or more processing platforms. Illustrative embodiments of such platforms will now be described in greater detail. These and other processing platforms may be used to implement at least portions of other information processing systems in other embodiments. A given such processing platform comprises at least one processing device comprising a processor coupled to a memory. 
     One illustrative embodiment of a processing platform that may be used to implement at least a portion of an information processing system comprises cloud infrastructure including virtual machines implemented using a hypervisor that runs on physical infrastructure. The cloud infrastructure further comprises sets of applications running on respective ones of the virtual machines under the control of the hypervisor. It is also possible to use multiple hypervisors each providing a set of virtual machines using at least one underlying physical machine. Different sets of virtual machines provided by one or more hypervisors may be utilized in configuring multiple instances of various components of the system. 
     These and other types of cloud infrastructure can be used to provide what is also referred to herein as a multi-tenant environment. One or more system components such as virtual machines, or portions thereof, are illustratively implemented for use by tenants of such a multi-tenant environment. 
     Cloud infrastructure as disclosed herein can include cloud-based systems such as Amazon Web Services, Google Cloud Platform and Microsoft Azure. Virtual machines provided in such systems can be used to implement a fast tier or other front-end tier of a multi-tier storage system in illustrative embodiments. A capacity tier or other back-end tier of such a multi-tier storage system can be implemented using one or more object stores such as Amazon S3, Google Cloud Platform Cloud Storage, and Microsoft Azure Blob Storage. 
     In some embodiments, the cloud infrastructure additionally or alternatively comprises a plurality of containers illustratively implemented using respective operating system kernel control groups of one or more container host devices. For example, a given container of cloud infrastructure illustratively comprises a Docker container or other type of LXC implemented using a kernel control group. The containers may run on virtual machines in a multi-tenant environment, although other arrangements are possible. The containers may be utilized to implement a variety of different types of functionality within the system  100 . For example, containers can be used to implement respective compute nodes or storage nodes of a cloud-based system. Again, containers may be used in combination with other virtualization infrastructure such as virtual machines implemented using a hypervisor. 
     Another illustrative embodiment of a processing platform that may be used to implement at least a portion of an information processing system comprises a plurality of processing devices which communicate with one another over at least one network. The network may comprise any type of network, including by way of example a global computer network such as the Internet, a WAN, a LAN, a satellite network, a telephone or cable network, a cellular network, a wireless network such as a WiFi or WiMAX network, or various portions or combinations of these and other types of networks. 
     Each processing device of the processing platform comprises a processor coupled to a memory. The processor may comprise a microprocessor, a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a graphics processing unit (GPU) or other type of processing circuitry, as well as portions or combinations of such circuitry elements. The memory may comprise random access memory (RAM), read-only memory (ROM), flash memory or other types of memory, in any combination. The memory and other memories disclosed herein should be viewed as illustrative examples of what are more generally referred to as “processor-readable storage media” storing executable program code of one or more software programs. 
     Articles of manufacture comprising such processor-readable storage media are considered illustrative embodiments. A given such article of manufacture may comprise, for example, a storage array, a storage disk or an integrated circuit containing RAM, ROM, flash memory or other electronic memory, or any of a wide variety of other types of computer program products. The term “article of manufacture” as used herein should be understood to exclude transitory, propagating signals. 
     Also included in the processing device is network interface circuitry, which is used to interface the processing device with the network and other system components, and may comprise conventional transceivers. 
     As another example, portions of a given processing platform in some embodiments can comprise converged infrastructure such as VxRail™, VxRack™, VxRack™ FLEX, VxBlock™ or Vblock® converged infrastructure from Dell Technologies. 
     Again, these particular processing platforms are presented by way of example only, and other embodiments may include additional or alternative processing platforms, as well as numerous distinct processing platforms in any combination, with each such platform comprising one or more computers, servers, storage devices or other processing devices. 
     It should therefore be understood that in other embodiments different arrangements of additional or alternative elements may be used. At least a subset of these elements may be collectively implemented on a common processing platform, or each such element may be implemented on a separate processing platform. 
     Also, numerous other arrangements of computers, servers, storage devices or other components are possible in an information processing system as disclosed herein. Such components can communicate with other elements of the information processing system over any type of network or other communication media. 
     As indicated previously, components of an information processing system as disclosed herein can be implemented at least in part in the form of one or more software programs stored in memory and executed by a processor of a processing device. For example, at least portions of the functionality of host devices  102 , SAN  104  and storage array  105  are illustratively implemented in the form of software running on one or more processing devices. As a more particular example, the instances of path selection logic  114 , access state request generation and analysis logic  116  and access state notification logic  122  may be implemented at least in part in software, as indicated previously herein. 
     It should again be emphasized that the above-described embodiments are presented for purposes of illustration only. Many variations and other alternative embodiments may be used. For example, the disclosed techniques are applicable to a wide variety of other types of information processing systems, utilizing other arrangements of host devices, networks, storage systems, storage arrays, storage devices, processors, memories, IO queues, MPIO drivers, path selection logic, access state request generation and analysis logic, access state notification logic and additional or alternative components. Also, the particular configurations of system and device elements and associated processing operations illustratively shown in the drawings can be varied in other embodiments. For example, a wide variety of different MPIO driver configurations and associated storage device access data receiving and processing arrangements can be used in other embodiments. Moreover, the various assumptions made above in the course of describing the illustrative embodiments should also be viewed as exemplary rather than as requirements or limitations. Numerous other alternative embodiments within the scope of the appended claims will be readily apparent to those skilled in the art.