Patent Publication Number: US-11656939-B2

Title: Storage cluster memory characterization

Description:
BACKGROUND 
     Solid-state memory, such as flash, is currently in use in solid-state drives (SSD) to augment or replace conventional hard disk drives (HDD), writable CD (compact disk) or writable DVD (digital versatile disk) drives, collectively known as spinning media, and tape drives, for storage of large amounts of data. Flash and other solid-state memories have operation and wear characteristics that differ from spinning media. Yet, many solid-state drives are designed to conform to hard disk drive standards for compatibility reasons, which makes it difficult to provide enhanced features or take advantage of unique aspects of flash and other solid-state memory. 
     It is within this context that the embodiments arise. 
     SUMMARY 
     In some embodiments, a method for die-level monitoring in a storage cluster is provided. The method includes distributing user data throughout a plurality of storage nodes through erasure coding, wherein the plurality of storage nodes are housed within a chassis that couples the storage nodes as a storage cluster. Each of the plurality of storage nodes has a non-volatile solid-state storage with non-volatile memory and the user data is accessible via the erasure coding from a remainder of the plurality of storage nodes in event of two of the plurality of storage nodes being unreachable. The method includes producing diagnostic information that diagnoses the non-volatile memory of the non-volatile solid-state storage of each of the plurality of storage nodes, on a basis of per package, per die, per plane, per block, or per page, the producing performed by each of the plurality of storage nodes. The method includes writing the diagnostic information to a memory in the storage cluster, wherein a processor performs at least one method operation. 
     Other aspects and advantages of the embodiments will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments. 
         FIG.  1    is a perspective view of a storage cluster with multiple storage nodes and internal storage coupled to each storage node to provide network attached storage, in accordance with some embodiments. 
         FIG.  2    is a system diagram of an enterprise computing system, which can use one or more of the storage clusters of  FIG.  1    as a storage resource in some embodiments. 
         FIG.  3    is a block diagram showing multiple storage nodes and non-volatile solid-state storage with differing capacities, suitable for use in the storage cluster of  FIG.  1    in accordance with some embodiments. 
         FIG.  4    is a block diagram showing an interconnect switch coupling multiple storage nodes in accordance with some embodiments. 
         FIG.  5    is a multiple level block diagram, showing contents of a storage node and contents of one of the non-volatile solid-state storage units in accordance with some embodiments. 
         FIG.  6    is a multiple level block diagram, showing a controller, flash dies, and interior details of flash dies in accordance with some embodiments. 
         FIG.  7    is a flow diagram of a method for die-level monitoring in a storage array, which can be practiced on or by embodiments of the storage cluster, storage nodes and/or non-volatile solid-state storages in accordance with some embodiments. 
         FIG.  8    is an illustration showing an exemplary computing device which may implement the embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments below describe a storage cluster that stores user data, such as user data originating from one or more user or client systems or other sources external to the storage cluster. The storage cluster distributes user data across storage nodes housed within a chassis, using erasure coding and redundant copies of metadata. Erasure coding refers to a method of data protection or reconstruction in which data is stored across a set of different locations, such as disks, storage nodes or geographic locations. Flash memory is one type of solid-state memory that may be integrated with the embodiments, although the embodiments may be extended to other types of solid-state memory or other storage medium, including non-solid-state memory. Control of storage locations and workloads are distributed across the storage locations in a clustered peer-to-peer system. Tasks such as mediating communications between the various storage nodes, detecting when a storage node has become unavailable, and balancing I/Os (inputs and outputs) across the various storage nodes, are all handled on a distributed basis. Data is laid out or distributed across multiple storage nodes in data fragments or stripes that support data recovery in some embodiments. Ownership of data can be reassigned within a cluster, independent of input and output patterns. This architecture described in more detail below allows a storage node in the cluster to fail, with the system remaining operational, since the data can be reconstructed from other storage nodes and thus remain available for input and output operations. In various embodiments, a storage node may be referred to as a cluster node, a blade, or a server. 
     The storage cluster is contained within a chassis, i.e., an enclosure housing one or more storage nodes. A mechanism to provide power to each storage node, such as a power distribution bus, and a communication mechanism, such as a communication bus that enables communication between the storage nodes are included within the chassis. The storage cluster can run as an independent system in one location according to some embodiments. In one embodiment, a chassis contains at least two instances of the power distribution and the internal and external communication bus which may be enabled or disabled independently. The internal communication bus may be an Ethernet bus, however, other technologies such as Peripheral Component Interconnect (PCI) Express, InfiniBand, and others, are equally suitable. The chassis provides a port for an external communication bus for enabling communication between multiple chassis, directly or through a switch, and with client systems. The external communication may use a technology such as Ethernet, InfiniBand, Fibre Channel, etc. In some embodiments, the external communication bus uses different communication bus technologies for inter-chassis and client communication. If a switch is deployed within or between chassis, the switch may act as a translation between multiple protocols or technologies. When multiple chassis are connected to define a storage cluster, the storage cluster may be accessed by a client using either proprietary interfaces or standard interfaces such as network file system (NFS), common internet file system (CIFS), small computer system interface (SCSI) or hypertext transfer protocol (HTTP). Translation from the client protocol may occur at the switch, chassis external communication bus or within each storage node. 
     Each storage node may be one or more storage servers and each storage server is connected to one or more non-volatile solid-state memory units, which may be referred to as storage units. One embodiment includes a single storage server in each storage node and between one to eight non-volatile solid-state memory units, however this one example is not meant to be limiting. The storage server may include a processor, dynamic random access memory (DRAM) and interfaces for the internal communication bus and power distribution for each of the power buses. Inside the storage node, the interfaces and storage unit share a communication bus, e.g., PCI Express, in some embodiments. The non-volatile solid-state memory units may directly access the internal communication bus interface through a storage node communication bus, or request the storage node to access the bus interface. The non-volatile solid-state memory unit contains an embedded central processing unit (CPU), solid-state storage controller, and a quantity of solid-state mass storage, e.g., between 2-32 terabytes (TB) in some embodiments. An embedded volatile storage medium, such as DRAM, and an energy reserve apparatus are included in the non-volatile solid-state memory unit. In some embodiments, the energy reserve apparatus is a capacitor, super-capacitor, or battery that enables transferring a subset of DRAM contents to a stable storage medium in the case of power loss. In some embodiments, the non-volatile solid-state memory unit is constructed with a storage class memory, such as phase change or other resistive random access memory (RRAM) or magnetoresistive random access memory (MRAM) that substitutes for DRAM and enables a reduced power hold-up apparatus. 
     One of many features of the storage nodes and non-volatile solid-state storage units discussed below is the ability to track and provide diagnostic information about flash memory on a per package, die, plane, block or page basis. Flash wear, changes or trends can be tracked over time. In some embodiments, flash writes or reads can be biased, based on the diagnostic information. A flash block with a relatively high level of wear can be avoided for new writes, which are instead directed to flash blocks with lower levels of wear. These and further details of the storage memory are discussed below. 
       FIG.  1    is a perspective view of a storage cluster  160 , with multiple storage nodes  150  and internal solid-state memory coupled to each storage node to provide network attached storage or storage area network, in accordance with some embodiments. A network attached storage, storage area network, or a storage cluster, or other storage memory, could include one or more storage clusters  160 , each having one or more storage nodes  150 , in a flexible and reconfigurable arrangement of both the physical components and the amount of storage memory provided thereby. The storage cluster  160  is designed to fit in a rack, and one or more racks can be set up and populated as desired for the storage memory. The storage cluster  160  has a chassis  138  having multiple slots  142 . It should be appreciated that chassis  138  may be referred to as a housing, enclosure, or rack unit. In one embodiment, the chassis  138  has fourteen slots  142 , although other numbers of slots are readily devised. For example, some embodiments have four slots, eight slots, sixteen slots, thirty-two slots, or other suitable number of slots. Each slot  142  can accommodate one storage node  150  in some embodiments. Chassis  138  includes flaps  148  that can be utilized to mount the chassis  138  on a rack. Fans  144  provide air circulation for cooling of the storage nodes  150  and components thereof, although other cooling components could be used, or an embodiment could be devised without cooling components. A switch fabric  146  couples storage nodes  150  within chassis  138  together and to a network for communication to the memory. In an embodiment depicted in  FIG.  1   , the slots  142  to the left of the switch fabric  146  and fans  144  are shown occupied by storage nodes  150 , while the slots  142  to the right of the switch fabric  146  and fans  144  are empty and available for insertion of storage node  150  for illustrative purposes. This configuration is one example, and one or more storage nodes  150  could occupy the slots  142  in various further arrangements. The storage node arrangements need not be sequential or adjacent in some embodiments. Storage nodes  150  are hot pluggable, meaning that a storage node  150  can be inserted into a slot  142  in the chassis  138 , or removed from a slot  142 , without stopping or powering down the system. Upon insertion or removal of storage node  150  from slot  142 , the system automatically reconfigures in order to recognize and adapt to the change. Reconfiguration, in some embodiments, includes restoring redundancy and/or rebalancing data or load. 
     Each storage node  150  can have multiple components. In the embodiment shown here, the storage node  150  includes a printed circuit board  158  populated by a CPU  156 , i.e., processor, a memory  154  coupled to the CPU  156 , and a non-volatile solid-state storage  152  coupled to the CPU  156 , although other mountings and/or components could be used in further embodiments. The memory  154  has instructions which are executed by the CPU  156  and/or data operated on by the CPU  156 . As further explained below, the non-volatile solid-state storage  152  includes flash or, in further embodiments, other types of solid-state memory. 
       FIG.  2    is a system diagram of an enterprise computing system  102 , which can use one or more of the storage nodes, storage clusters and/or non-volatile solid-state storage of  FIG.  1    as a storage resource  108 . For example, flash storage  128  of  FIG.  2    may integrate the storage nodes, storage clusters and/or non-volatile solid-state storage of  FIG.  1    in some embodiments. The enterprise computing system  102  has processing resources  104 , networking resources  106  and storage resources  108 , including flash storage  128 . A flash controller  130  and flash memory  132  are included in the flash storage  128 . In various embodiments, the flash storage  128  could include one or more storage nodes or storage clusters, with the flash controller  130  including the CPUs, and the flash memory  132  including the non-volatile solid-state storage of the storage nodes. In some embodiments flash memory  132  may include different types of flash memory or the same type of flash memory. The enterprise computing system  102  illustrates an environment suitable for deployment of the flash storage  128 , although the flash storage  128  could be used in other computing systems or devices, larger or smaller, or in variations of the enterprise computing system  102 , with fewer or additional resources. The enterprise computing system  102  can be coupled to a network  140 , such as the Internet, in order to provide or make use of services. For example, the enterprise computing system  102  could provide cloud services, physical computing resources, or virtual computing services. 
     In the enterprise computing system  102 , various resources are arranged and managed by various controllers. A processing controller  110  manages the processing resources  104 , which include processors  116  and random-access memory (RAM)  118 . Networking controller  112  manages the networking resources  106 , which include routers  120 , switches  122 , and servers  124 . A storage controller  114  manages storage resources  108 , which include hard drives  126  and flash storage  128 . Other types of processing resources, networking resources, and storage resources could be included with the embodiments. In some embodiments, the flash storage  128  completely replaces the hard drives  126 . The enterprise computing system  102  can provide or allocate the various resources as physical computing resources, or in variations, as virtual computing resources supported by physical computing resources. For example, the various resources could be implemented using one or more servers executing software. Files or data objects, or other forms of data, are stored in the storage resources  108 . 
     In various embodiments, an enterprise computing system  102  could include multiple racks populated by storage clusters, and these could be located in a single physical location such as in a cluster or a server farm. In other embodiments the multiple racks could be located at multiple physical locations such as in various cities, states or countries, connected by a network. Each of the racks, each of the storage clusters, each of the storage nodes, and each of the non-volatile solid-state storage could be individually configured with a respective amount of storage space, which is then reconfigurable independently of the others. Storage capacity can thus be flexibly added, upgraded, subtracted, recovered and/or reconfigured at each of the non-volatile solid-state storages. As mentioned previously, each storage node could implement one or more servers in some embodiments. 
       FIG.  3    is a block diagram showing multiple storage nodes  150  and non-volatile solid-state storage  152  with differing capacities, suitable for use in the chassis of  FIG.  1   . Each storage node  150  can have one or more units of non-volatile solid-state storage  152 . Each non-volatile solid-state storage  152  may include differing capacity from other non-volatile solid-state storage  152  on a storage node  150  or in other storage nodes  150  in some embodiments. Alternatively, all of the non-volatile solid-state storages  152  on a storage node or on multiple storage nodes can have the same capacity or combinations of the same and/or differing capacities. This flexibility is illustrated in  FIG.  3   , which shows an example of one storage node  150  having mixed non-volatile solid-state storage  152  of four, eight and thirty-two TB capacity, another storage node  150  having non-volatile solid-state storage  152  each of thirty-two TB capacity, and still another storage node having non-volatile solid-state storage  152  each of eight TB capacity. Various further combinations and capacities are readily devised in accordance with the teachings herein. In the context of clustering, e.g., clustering storage to form a storage cluster, a storage node can be or include a non-volatile solid-state storage  152 . Non-volatile solid-state storage  152  is a convenient clustering point as the non-volatile solid-state storage  152  may include a non-volatile random access memory (NVRAM) component, as will be further described below. 
     Referring to  FIGS.  1  and  3   , storage cluster  160  is scalable, meaning that storage capacity with non-uniform storage sizes is readily added, as described above. One or more storage nodes  150  can be plugged into or removed from each chassis and the storage cluster self-configures in some embodiments. Plug-in storage nodes  150 , whether installed in a chassis as delivered or later added, can have different sizes. For example, in one embodiment a storage node  150  can have any multiple of 4 TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, a storage node  150  could have any multiple of other storage amounts or capacities. Storage capacity of each storage node  150  is broadcast, and influences decisions of how to stripe the data. For maximum storage efficiency, an embodiment can self-configure as wide as possible in the stripe, subject to a predetermined requirement of continued operation with loss of up to one, or up to two, non-volatile solid-state storage units  152  or storage nodes  150  within the chassis. 
       FIG.  4    is a block diagram showing a communications interconnect  170  and power distribution bus  172  coupling multiple storage nodes  150 . Referring back to  FIG.  1   , the communications interconnect  170  can be included in or implemented with the switch fabric  146  in some embodiments. Where multiple storage clusters  160  occupy a rack, the communications interconnect  170  can be included in or implemented with a top of rack switch, in some embodiments. As illustrated in  FIG.  4   , storage cluster  160  is enclosed within a single chassis  138 . External port  176  is coupled to storage nodes  150  through communications interconnect  170 , while external port  174  is coupled directly to a storage node. External power port  178  is coupled to power distribution bus  172 . Storage nodes  150  may include varying amounts and differing capacities of non-volatile solid-state storage  152  as described with reference to  FIG.  3   . In addition, one or more storage nodes  150  may be a compute only storage node as illustrated in  FIG.  4   . Authorities  168  are implemented on the non-volatile solid-state storages  152 , for example as lists or other data structures stored in memory. In some embodiments the authorities are stored within the non-volatile solid-state storage  152  and supported by software executing on a controller or other processor of the non-volatile solid-state storage  152 . In a further embodiment, authorities  168  are implemented on the storage nodes  150 , for example as lists or other data structures stored in the memory  154  and supported by software executing on the CPU  156  of the storage node  150 . Authorities  168  control how and where data is stored in the non-volatile solid-state storages  152  in some embodiments. This control assists in determining which type of erasure coding scheme is applied to the data, and which storage nodes  150  have which portions of the data. Each authority  168  may be assigned to a non-volatile solid-state storage  152 . Each authority may control a range of inode numbers, segment numbers, or other data identifiers which are assigned to data by a file system, by the storage nodes  150 , or by the non-volatile solid-state storage  152 , in various embodiments. 
     Every piece of data, and every piece of metadata, has redundancy in the system in some embodiments. In addition, every piece of data and every piece of metadata has an owner, which may be referred to as an authority. If that authority is unreachable, for example through failure of a storage node, there is a plan of succession for how to find that data or that metadata. In various embodiments, there are redundant copies of authorities  168 . Authorities  168  have a relationship to storage nodes  150  and non-volatile solid-state storage  152  in some embodiments. Each authority  168 , covering a range of data segment numbers or other identifiers of the data, may be assigned to a specific non-volatile solid-state storage  152 . In some embodiments the authorities  168  for all of such ranges are distributed over the non-volatile solid-state storages  152  of a storage cluster. Each storage node  150  has a network port that provides access to the non-volatile solid-state storage(s)  152  of that storage node  150 . Data can be stored in a segment, which is associated with a segment number and that segment number is an indirection for a configuration of a RAID (redundant array of independent disks) stripe in some embodiments. The assignment and use of the authorities  168  thus establishes an indirection to data. Indirection may be referred to as the ability to reference data indirectly, in this case via an authority  168 , in accordance with some embodiments. A segment identifies a set of non-volatile solid-state storage  152  and a local identifier into the set of non-volatile solid-state storage  152  that may contain data. In some embodiments, the local identifier is an offset into the device and may be reused sequentially by multiple segments. In other embodiments the local identifier is unique for a specific segment and never reused. The offsets in the non-volatile solid-state storage  152  are applied to locating data for writing to or reading from the non-volatile solid-state storage  152  (in the form of a RAID stripe). Data is striped across multiple units of non-volatile solid-state storage  152 , which may include or be different from the non-volatile solid-state storage  152  having the authority  168  for a particular data segment. 
     If there is a change in where a particular segment of data is located, e.g., during a data move or a data reconstruction, the authority  168  for that data segment should be consulted, at that non-volatile solid-state storage  152  or storage node  150  having that authority  168 . In order to locate a particular piece of data, embodiments calculate a hash value for a data segment or apply an inode number or a data segment number. The output of this operation points to a non-volatile solid-state storage  152  having the authority  168  for that particular piece of data. In some embodiments there are two stages to this operation. The first stage maps an entity identifier (ID), e.g., a segment number, inode number, or directory number to an authority identifier. This mapping may include a calculation such as a hash or a bit mask. The second stage is mapping the authority identifier to a particular non-volatile solid-state storage  152 , which may be done through an explicit mapping. The operation is repeatable, so that when the calculation is performed, the result of the calculation repeatably and reliably points to a particular non-volatile solid-state storage  152  having that authority  168 . The operation may include the set of reachable storage nodes as input. If the set of reachable non-volatile solid-state storage units changes the optimal set changes. In some embodiments, the persisted value is the current assignment (which is always true) and the calculated value is the target assignment the cluster will attempt to reconfigure towards. This calculation may be used to determine the optimal non-volatile solid-state storage  152  for an authority in the presence of a set of non-volatile solid-state storage  152  that are reachable and constitute the same cluster. The calculation also determines an ordered set of peer non-volatile solid-state storage  152  that will also record the authority to non-volatile solid-state storage mapping so that the authority may be determined even if the assigned non-volatile solid-state storage is unreachable. A duplicate or substitute authority  168  may be consulted if a specific authority  168  is unavailable in some embodiments. 
     With reference to  FIGS.  1 - 4   , two of the many tasks of the CPU  156  on a storage node  150  are to break up write data, and reassemble read data. When the system has determined that data is to be written, the authority  168  for that data is located as above. When the segment ID for data is already determined the request to write is forwarded to the non-volatile solid-state storage  152  currently determined to be the host of the authority  168  determined from the segment. The host CPU  156  of the storage node  150 , on which the non-volatile solid-state storage  152  and corresponding authority  168  reside, then breaks up or shards the data and transmits the data out to various non-volatile solid-state storage  152 . The transmitted data is written as a data stripe in accordance with an erasure coding scheme. In some embodiments, data is requested to be pulled, and in other embodiments, data is pushed. In reverse, when data is read, the authority  168  for the segment ID containing the data is located as described above. The host CPU  156  of the storage node  150  on which the non-volatile solid-state storage  152  and corresponding authority  168  reside requests the data from the non-volatile solid-state storage and corresponding storage nodes pointed to by the authority. In some embodiments the data is read from flash storage as a data stripe. The host CPU  156  of storage node  150  then reassembles the read data, correcting any errors (if present) according to the appropriate erasure coding scheme, and forwards the reassembled data to the network. In further embodiments, some or all of these tasks can be handled in the non-volatile solid-state storage  152 . In some embodiments, the segment host requests the data be sent to storage node  150  by requesting pages from storage and then sending the data to the storage node making the original request. 
     In some systems, for example in UNIX-style file systems, data is handled with an index node or inode, which specifies a data structure that represents an object in a file system. The object could be a file or a directory, for example. Metadata may accompany the object, as attributes such as permission data and a creation timestamp, among other attributes. A segment number could be assigned to all or a portion of such an object in a file system. In other systems, data segments are handled with a segment number assigned elsewhere. For purposes of discussion, the unit of distribution is an entity, and an entity can be a file, a directory or a segment. That is, entities are units of data or metadata stored by a storage system. Entities are grouped into sets called authorities. Each authority has an authority owner, which is a storage node that has the exclusive right to update the entities in the authority. In other words, a storage node contains the authority, and that the authority, in turn, contains entities. 
     A segment is a logical container of data in accordance with some embodiments. A segment is an address space between medium address space and physical flash locations, i.e., the data segment number, are in this address space. Segments may also contain meta-data, which enable data redundancy to be restored (rewritten to different flash locations or devices) without the involvement of higher level software. In one embodiment, an internal format of a segment contains client data and medium mappings to determine the position of that data. Each data segment is protected, e.g., from memory and other failures, by breaking the segment into a number of data and parity shards, where applicable. The data and parity shards are distributed, i.e., striped, across non-volatile solid-state storage  152  coupled to the host CPUs  156  (See  FIG.  5   ) in accordance with an erasure coding scheme. Usage of the term segments refers to the container and its place in the address space of segments in some embodiments. Usage of the term stripe refers to the same set of shards as a segment and includes how the shards are distributed along with redundancy or parity information in accordance with some embodiments. 
     A series of address-space transformations takes place across an entire storage system. At the top is the directory entries (file names) which link to an inode. Modes point into medium address space, where data is logically stored. Medium addresses may be mapped through a series of indirect mediums to spread the load of large files, or implement data services like deduplication or snapshots. Medium addresses may be mapped through a series of indirect mediums to spread the load of large files, or implement data services like deduplication or snapshots. Segment addresses are then translated into physical flash locations. Physical flash locations have an address range bounded by the amount of flash in the system in accordance with some embodiments. Medium addresses and segment addresses are logical containers, and in some embodiments use a 128 bit or larger identifier so as to be practically infinite, with a likelihood of reuse calculated as longer than the expected life of the system. Addresses from logical containers are allocated in a hierarchical fashion in some embodiments. Initially, each non-volatile solid-state storage  152  may be assigned a range of address space. Within this assigned range, the non-volatile solid-state storage  152  is able to allocate addresses without synchronization with other non-volatile solid-state storage  152 . 
     Data and metadata is stored by a set of underlying storage layouts that are optimized for varying workload patterns and storage devices. These layouts incorporate multiple redundancy schemes, compression formats and index algorithms. Some of these layouts store information about authorities and authority masters, while others store file metadata and file data. The redundancy schemes include error correction codes that tolerate corrupted bits within a single storage device (such as a NAND flash chip), erasure codes that tolerate the failure of multiple storage nodes, and replication schemes that tolerate data center or regional failures. In some embodiments, low density parity check (LDPC) code is used within a single storage unit. Reed-Solomon encoding is used within a storage cluster, and mirroring is used within a storage grid in some embodiments. Metadata may be stored using an ordered log structured index (such as a Log Structured Merge Tree), and large data may not be stored in a log structured layout. 
     In order to maintain consistency across multiple copies of an entity, the storage nodes agree implicitly on two things through calculations: (1) the authority that contains the entity, and (2) the storage node that contains the authority. The assignment of entities to authorities can be done by pseudorandomly assigning entities to authorities, by splitting entities into ranges based upon an externally produced key, or by placing a single entity into each authority. Examples of pseudorandom schemes are linear hashing and the Replication Under Scalable Hashing (RUSH) family of hashes, including Controlled Replication Under Scalable Hashing (CRUSH). In some embodiments, pseudo-random assignment is utilized only for assigning authorities to nodes because the set of nodes can change. The set of authorities cannot change so any subjective function may be applied in these embodiments. Some placement schemes automatically place authorities on storage nodes, while other placement schemes rely on an explicit mapping of authorities to storage nodes. In some embodiments, a pseudorandom scheme is utilized to map from each authority to a set of candidate authority owners. A pseudorandom data distribution function related to CRUSH may assign authorities to storage nodes and create a list of where the authorities are assigned. Each storage node has a copy of the pseudorandom data distribution function, and can arrive at the same calculation for distributing, and later finding or locating an authority. Each of the pseudorandom schemes requires the reachable set of storage nodes as input in some embodiments in order to conclude the same target nodes. Once an entity has been placed in an authority, the entity may be stored on physical devices so that no expected failure will lead to unexpected data loss. In some embodiments, rebalancing algorithms attempt to store the copies of all entities within an authority in the same layout and on the same set of machines. 
     Examples of expected failures include device failures, stolen machines, datacenter fires, and regional disasters, such as nuclear or geological events. Different failures lead to different levels of acceptable data loss. In some embodiments, a stolen storage node impacts neither the security nor the reliability of the system, while depending on system configuration, a regional event could lead to no loss of data, a few seconds or minutes of lost updates, or even complete data loss. 
     In the embodiments, the placement of data for storage redundancy is independent of the placement of authorities for data consistency. In some embodiments, storage nodes that contain authorities do not contain any persistent storage. Instead, the storage nodes are connected to non-volatile solid-state storage units that do not contain authorities. The communications interconnect between storage nodes and non-volatile solid-state storage units consists of multiple communication technologies and has non-uniform performance and fault tolerance characteristics. In some embodiments, as mentioned above, non-volatile solid-state storage units are connected to storage nodes via PCI express, storage nodes are connected together within a single chassis using Ethernet backplane, and chassis are connected together to form a storage cluster. Storage clusters are connected to clients using Ethernet or fiber channel in some embodiments. If multiple storage clusters are configured into a storage grid, the multiple storage clusters are connected using the Internet or other long-distance networking links, such as a “metro scale” link or private link that does not traverse the internet. 
     Authority owners have the exclusive right to modify entities, to migrate entities from one non-volatile solid-state storage unit to another non-volatile solid-state storage unit, and to add and remove copies of entities. This allows for maintaining the redundancy of the underlying data. When an authority owner fails, is going to be decommissioned, or is overloaded, the authority is transferred to a new storage node. Transient failures make it non-trivial to ensure that all non-faulty machines agree upon the new authority location. The ambiguity that arises due to transient failures can be achieved automatically by a consensus protocol such as Paxos, hot-warm failover schemes, via manual intervention by a remote system administrator, or by a local hardware administrator (such as by physically removing the failed machine from the cluster, or pressing a button on the failed machine). In some embodiments, a consensus protocol is used, and failover is automatic. If too many failures or replication events occur in too short a time period, the system goes into a self-preservation mode and halts replication and data movement activities until an administrator intervenes in accordance with some embodiments. 
     As authorities are transferred between storage nodes and authority owners update entities in their authorities, the system transfers messages between the storage nodes and non-volatile solid-state storage units. With regard to persistent messages, messages that have different purposes are of different types. Depending on the type of the message, the system maintains different ordering and durability guarantees. As the persistent messages are being processed, the messages are temporarily stored in multiple durable and non-durable storage hardware technologies. In some embodiments, messages are stored in RAM, NVRAM and on NAND flash devices, and a variety of protocols are used in order to make efficient use of each storage medium. Latency-sensitive client requests may be persisted in replicated NVRAM, and then later NAND, while background rebalancing operations are persisted directly to NAND. 
     Persistent messages are persistently stored prior to being replicated. This allows the system to continue to serve client requests despite failures and component replacement. Although many hardware components contain unique identifiers that are visible to system administrators, manufacturer, hardware supply chain and ongoing monitoring quality control infrastructure, applications running on top of the infrastructure address virtualize addresses. These virtualized addresses do not change over the lifetime of the storage system, regardless of component failures and replacements. This allows each component of the storage system to be replaced over time without reconfiguration or disruptions of client request processing. 
     In some embodiments, the virtualized addresses are stored with sufficient redundancy. A continuous monitoring system correlates hardware and software status and the hardware identifiers. This allows detection and prediction of failures due to faulty components and manufacturing details. The monitoring system also enables the proactive transfer of authorities and entities away from impacted devices before failure occurs by removing the component from the critical path in some embodiments. 
       FIG.  5    is a multiple level block diagram, showing contents of a storage node  150  and contents of a non-volatile solid-state storage  152  of the storage node  150 . Data is communicated to and from the storage node  150  by a network interface controller (NIC)  202  in some embodiments. Each storage node  150  has a CPU  156 , and one or more non-volatile solid-state storage  152 , as discussed above. Moving down one level in  FIG.  5   , each non-volatile solid-state storage  152  has a relatively fast non-volatile solid-state memory, such as non-volatile random access memory (NVRAM)  204 , and flash memory  206 . In some embodiments, NVRAM  204  may be a component that does not require program/erase cycles (e.g., DRAM, MRAM, or phase change memory (PCM)), and can be a memory that can support being written vastly more often than the memory is read from. Moving down another level in  FIG.  5   , the NVRAM  204  is implemented in one embodiment as high speed volatile memory, such as dynamic random access memory (DRAM)  216 , backed up by energy reserve  218 . Energy reserve  218  provides sufficient electrical power to keep the DRAM  216  powered long enough for contents to be transferred to the flash memory  206  in the event of power failure. In some embodiments, energy reserve  218  is a capacitor, super-capacitor, battery, or other device, that supplies a suitable supply of energy sufficient to enable the transfer of the contents of DRAM  216  to a stable storage medium in the case of power loss. The flash memory  206  is implemented as multiple flash dies  222 , which may be referred to as packages of flash dies  222  or an array of flash dies  222 . It should be appreciated that the flash dies  222  could be packaged in any number of ways, with a single die per package, multiple dies per package (i.e. multichip packages), in hybrid packages, as dies on a printed circuit board or other substrate. In some embodiments, the hybrid package may include a combination of memory types, such as NVRAM, random access memory (RAM), CPU, field programmable gate array (FPGA), or different sized flash memory in the same package. In the embodiment shown, the non-volatile solid-state storage  152  has a controller  212  or other processor, and an input output (I/O) port  210  coupled to the controller  212 . I/O port  210  is coupled to the CPU  156  and/or the network interface controller  202  of the flash storage node  150 . Flash input output (I/O) port  220  is coupled to the flash dies  222 , and a direct memory access unit (DMA)  214  is coupled to the controller  212 , the DRAM  216  and the flash dies  222 . In the embodiment shown, the I/O port  210 , controller  212 , DMA unit  214  and flash I/O port  220  are implemented on a programmable logic device (PLD)  208 , e.g., a field programmable gate array (FPGA). In this embodiment, each flash die  222  has pages, organized as sixteen kB (kilobyte) pages  224 , and a register  226  through which data can be written to or read from the flash die  222 . In further embodiments, other types of solid-state memory are used in place of, or in addition to flash memory illustrated within flash die  222 . 
       FIG.  6    is a multiple level block diagram, showing a controller  212 , flash dies  222 , and interior details of flash dies  222 . Diagnostic information relating to the flash memory  206  can be obtained on a per flash package  602 , per flash die  222 , per flash plane  604 , per flash block  606 , and/or per flash page  224  basis across the entirety of a storage cluster  160 , in some embodiments. In the example shown in  FIG.  6   , the flash memory  206  includes multiple flash packages  602 . Each flash package  602  includes multiple flash dies  222 , each of which in turn includes multiple flash planes  604 . Each flash plane  604  includes multiple flash blocks  606  each of which in turn includes multiple flash pages  224 . The diagnostic information is gathered or generated by the controller  212  of each non-volatile solid-state storage unit and forwarded to the CPU  156  of the corresponding storage node. In some embodiments, the CPU  156  performs further analysis on the diagnostic information and generates further diagnostic information. The controller  212  and/or the CPU  156  can write the diagnostic information to a memory in the storage cluster, for example the flash memory  206  or the DRAM  216  of a non-volatile solid-state storage unit, the memory  154  (See  FIG.  1   ) coupled to the CPU  156  in a storage node, or other memory of the storage cluster, storage node, or non-volatile solid-state storage unit. The diagnostic information can be stored as metadata, in some embodiments. 
     One type of diagnostic information is obtained by tracking bit errors per flash page  224  or per codeword. Each flash page  224  has multiple codewords, in some embodiments. Incidents of error correction could be reported and these incidents may be used as a source on which to base the diagnostic information. For example, the controller  212  could track bit errors of the flash memory  206  and forward the information about the bit errors to the CPU  156 , which could then tabulate this and/or generate further diagnostic information. Bit errors, or error corrections, can be tracked from feedback from an error correction block  608  in the controller  212  in some embodiments. The CPU  156  or the controller  212  could track wear of flash blocks  606  in the flash memory  206 , e.g., by establishing and updating a wear list in memory coupled as described above, responsive to or based on some of the diagnostic information. Such tracking could include ranking flash blocks  606  as to levels of wear, or comparing flash blocks  606  as to levels of wear. The flash memory  206  can be characterized over time, based on the diagnostic information. Characterization information could indicate changes or trends in the flash memory  206 , such as increases in the rate of errors or error correction over time. This characterization can be performed at any of the levels of granularity discussed above. 
     In some embodiments, the characterization or diagnostic information combines lower-level information from the flash memory  206  itself, such as bit error rates or types of errors (e.g. a zero is read as a one or a one is read as a zero), with higher-level application data. The higher-level application data could include retention time (e.g. how long a particular piece of data has been in the flash memory  206 ), file type, frequencies or relative arrival times of updates, erases or writes for specific files or other pieces of data, inter-arrival times, performance metrics, cacheability, etc. For example, the wear list expresses wear per flash package  602 , die  222 , block  606  or other portion of flash memory  206 , in terms of age, number of reads, number of writes, number of erasure cycles, and/or other parameters. In some embodiments, a retention list is established and maintained, which tracks how old data is in a particular flash package  602 , die  222 , block  606  or other portion of flash memory, i.e., how long the data has resided since it was last written. Either of these metrics, or a combination of these or other metrics, could be used to characterize the flash memory. Temperature, in a temperature list or table, could also be used. Various further tables and categories for characterizing flash could be added. In this manner, monitoring of the flash memory  206  is combined across multiple dimensions of flash and system metrics. Results of the monitoring can be indexed into a table or other data structure, in order to determine changes to flash settings for specific portions of the flash memory  206  to optimize reads, writes or erases (e.g., to an address range). This is in contrast to standard solid-state drives, which do not have access to die-level monitoring, and cannot make adjustments to that level of granularity. 
     In some embodiments, the CPU  156  sends the diagnostic information, or summarizes the diagnostic information in a report and sends the report, via a network. The diagnostic information or the report could be sent to an appropriate person or organization, which could include an owner or operator of a storage cluster, a manufacturer of storage nodes, a manufacturer of flash memory  206 , flash packages  602  or flash dies  222  or other interested or authorized party. These reports could benefit the manufacturers, which can use the information for warranty service and/or to highlight manufacturing and reliability problems and guide improvements. The reports also benefit users, who can plan system maintenance, repairs and upgrades based on the details in the reports. Actual behavior of the flash memory  206  over time can be compared to predicted behavior or to warranties if applicable. 
     The CPU  156  or the controller  212  could make decisions based on the diagnostic information. For example, if it is determined that a flash block  606  has a high level of wear, the CPU  156  or the controller  212  could determine to write some of the user data to another flash block  606  with a lower level of wear. The controller  212  may bias a read from the flash memory, or a write to the flash memory  206 , as a response to producing or obtaining the diagnostic information. Depending on the type of flash, and whether specific features are available on flash dies  222 , this biasing can take different forms. Biasing the writes or the reads may extend the lifespan of some or all of the flash memory  206 . For example, some types of flash dies  222  may support a variable write time, a variable write voltage, a variable read time, a variable reference voltage, a variable reference current or a variable number of reads. The controller  212  could determine, based on the diagnostic information, to direct a flash die  222  to apply a specified value of one of the above variable parameters to a specified write or read. The specified value could be applied to specified writes or reads to flash pages  224 , flash blocks  606 , flash dies  222 , and/or flash packages  602 . The controller  212  could determine to apply a stronger error correction code for a particular flash page  224  or flash block  606 , or apply a different program and/or read mechanism to adjust for particular conditions such as high error rate, long retention time, and various combinations, etc. Thus, the granularity of the application of variable parameters to writes or reads of the flash memory  206  can match and be supported by the granularity of the diagnostic information itself. 
     The flash memory is a multi-dimensional space where sampling and extrapolation can be used. Data points that are close to sampling points for various dimensions (location, retention time, file type, etc.) can be used to predict what the ideal parameter settings should be for that operation, e.g., read, write, erase, etc. Predictions (based on matches and/or data extrapolation) are a type of use of the diagnostic information or system telemetry. In some embodiments, the controller  212  samples the reads or the writes of a particular flash page  224 , flash block  606 , flash die  222  or flash package  602 , determines diagnostic information, extrapolates, determines a parameter setting, and applies that parameter setting for an extrapolated region or space. 
     Continuing with the above examples, the variable parameters are applicable to multiple scenarios. In a case where a flash block  606  is experiencing an increase in read errors, the controller  212  could direct the flash block  606  to perform repeated reads at differing reference voltages or reference currents. If a variable reference voltage or a reference current is not available, the controller  212  could perform the multiple reads without varying the reference voltage or current. The controller  212 , or the CPU  156  could then perform statistical analysis of the reads and determine a most likely bit value for each read of data in the flash block  606 . In cases where a variable write parameter is supported in flash dies  222 , a value of a variable write parameter can be selected in an attempt to increase write or read reliability of the flash die  222 . Similarly, in cases where a variable read parameter is supported in flash dies  222 , a value of a variable read parameter can be selected in an attempt to increase read reliability of the flash die  222 . In some embodiments a value for a variable write or read parameter could be selected in response to a determination that some portion of flash memory  206  has greater wear relative to another portion. As a further example, some types of flash dies  222  may have and support changing from multilevel cell (MLC) operation to single cell (SLC) operation. SLC flash has one bit per cell, and MLC flash has more than one bit per cell. Examples of MLC flash include two bits per cell for four levels, three bits per cell (also known as triple level cell or TLC) for eight levels, four bits per cell (also known as quad level cell or QLC) and so on. The CPU  156  or the controller  212  could direct a flash die  222  to change from MLC operation to SLC operation in order to increase reliability of reads or writes. This change may be in response to determining that some portion of the flash memory  206  has greater wear relative to another portion. 
       FIG.  7    is a flow diagram of a method for die-level monitoring in a storage array, which can be practiced on or by embodiments of the storage cluster, storage nodes and/or non-volatile solid-state storages in accordance with some embodiments. Actions of the method can be performed by a processor, such as the CPU of a storage node or the controller of a non-volatile solid-state storage. User data is distributed throughout a plurality of storage nodes, with erasure coding, in an action  702 . The user data is accessible via the erasure coding, even if two of the storage nodes become unreachable. User data is read, with error correction as applicable, in an action  704 . Bit errors and/or error correction incidents are tracked, in an action  706 . Error information is forwarded from non-volatile solid-state storages to storage nodes, in an action  708 . 
     Continuing with  FIG.  7   , diagnostic information is generated at various levels, in an action  710 . For example, the diagnostic information could be generated at the level of the flash package, flash die, flash plane, flash block, or flash page. The flash memory is characterized over time, in an action  712 . This characterization could be performed at any or all of the above levels. The diagnostic information is sent to an appropriate destination possibly via a network, in an action  714 . In a decision action  716 , it is determined whether a flash block has a high level of wear. This determination is based on the diagnostic information. If the answer is no, flow branches back to the action  706 , to continue tracking bit errors or error correction. If the answer is yes, a flash block does have a high level of wear, flow proceeds to the decision action  718 . In the decision action  718 , it is determined whether to write to a differing flash block. If the answer is yes, the writing should be to a differing flash block, flow branches back to the action  706 , to continue tracking bit errors or error correction. If the answer is no, the writing should be to the block that has the high level of wear, flow proceeds to the decision action  720 . 
     In the decision action  720 , it is determined whether to bias a write. If the answer is no, flow proceeds to the decision action  724 . If the answer is yes, flow proceeds to the action  722  where a variable write parameter is determined and applied. In the decision action  724 , is determined whether to bias a read. If the answer is no, flow proceeds back to the action  706 , to continue tracking bit errors or error correction. If the answer is yes, flow proceeds to the action  726 . In the action  726 , a variable read parameter is determined and applied. Flow then proceeds back to the action  706 , to continue tracking bit errors or error correction. In variations of the above method, the determinations of whether to bias a write or a read could be made in differing orders, or could be based on other aspects of diagnostic information. Diagnostic information could be stored in various memory locations in a storage cluster. 
     It should be appreciated that the methods described herein may be performed with a digital processing system, such as a conventional, general-purpose computer system. Special purpose computers, which are designed or programmed to perform only one function may be used in the alternative.  FIG.  8    is an illustration showing an exemplary computing device which may implement the embodiments described herein. The computing device of  FIG.  8    may be used to perform embodiments of the functionality for a storage node or a non-volatile solid-state storage in accordance with some embodiments. The computing device includes a central processing unit (CPU)  801 , which is coupled through a bus  805  to a memory  803 , and mass storage device  807 . Mass storage device  807  represents a persistent data storage device such as a disc drive, which may be local or remote in some embodiments. The mass storage device  807  could implement a backup storage, in some embodiments. Memory  803  may include read only memory, random access memory, etc. Applications resident on the computing device may be stored on or accessed via a computer readable medium such as memory  803  or mass storage device  807  in some embodiments. Applications may also be in the form of modulated electronic signals modulated accessed via a network modem or other network interface of the computing device. It should be appreciated that CPU  801  may be embodied in a general-purpose processor, a special purpose processor, or a specially programmed logic device in some embodiments. 
     Display  811  is in communication with CPU  801 , memory  803 , and mass storage device  807 , through bus  805 . Display  811  is configured to display any visualization tools or reports associated with the system described herein. Input/output device  809  is coupled to bus  505  in order to communicate information in command selections to CPU  801 . It should be appreciated that data to and from external devices may be communicated through the input/output device  809 . CPU  801  can be defined to execute the functionality described herein to enable the functionality described with reference to  FIGS.  1 - 7   . The code embodying this functionality may be stored within memory  803  or mass storage device  807  for execution by a processor such as CPU  801  in some embodiments. The operating system on the computing device may be MS-WINDOWS™, UNIX™, LINUX™, iOS™, CentOS™, Android, Redhat Linux™, z/OS™, or other known operating systems. It should be appreciated that the embodiments described herein may be integrated with virtualized computing system also. 
     Detailed illustrative embodiments are disclosed herein. However, specific functional details disclosed herein are merely representative for purposes of describing embodiments. Embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. 
     It should be understood that although the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one step or calculation from another. For example, a first calculation could be termed a second calculation, and, similarly, a second step could be termed a first step, without departing from the scope of this disclosure. As used herein, the term “and/or” and the “/” symbol includes any and all combinations of one or more of the associated listed items. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     With the above embodiments in mind, it should be understood that the embodiments might employ various computer-implemented operations involving data stored in computer systems. These operations are those requiring physical manipulation of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. Further, the manipulations performed are often referred to in terms, such as producing, identifying, determining, or comparing. Any of the operations described herein that form part of the embodiments are useful machine operations. The embodiments also relate to a device or an apparatus for performing these operations. The apparatus can be specially constructed for the required purpose, or the apparatus can be a general-purpose computer selectively activated or configured by a computer program stored in the computer. In particular, various general-purpose machines can be used with computer programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized apparatus to perform the required operations. 
     A module, an application, a layer, an agent or other method-operable entity could be implemented as hardware, firmware, or a processor executing software, or combinations thereof. It should be appreciated that, where a software-based embodiment is disclosed herein, the software can be embodied in a physical machine such as a controller. For example, a controller could include a first module and a second module. A controller could be configured to perform various actions, e.g., of a method, an application, a layer or an agent. 
     The embodiments can also be embodied as computer readable code on a non-transitory computer readable medium. The computer readable medium is any data storage device that can store data, which can be thereafter read by a computer system. Examples of the computer readable medium include hard drives, network attached storage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and other optical and non-optical data storage devices. The computer readable medium can also be distributed over a network coupled computer system so that the computer readable code is stored and executed in a distributed fashion. Embodiments described herein may be practiced with various computer system configurations including hand-held devices, tablets, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers and the like. The embodiments can also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a wire-based or wireless network. 
     Although the method operations were described in a specific order, it should be understood that other operations may be performed in between described operations, described operations may be adjusted so that they occur at slightly different times or the described operations may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing. 
     In various embodiments, one or more portions of the methods and mechanisms described herein may form part of a cloud-computing environment. In such embodiments, resources may be provided over the Internet as services according to one or more various models. Such models may include Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). In IaaS, computer infrastructure is delivered as a service. In such a case, the computing equipment is generally owned and operated by the service provider. In the PaaS model, software tools and underlying equipment used by developers to develop software solutions may be provided as a service and hosted by the service provider. SaaS typically includes a service provider licensing software as a service on demand. The service provider may host the software, or may deploy the software to a customer for a given period of time. Numerous combinations of the above models are possible and are contemplated. 
     Various units, circuits, or other components may be described or claimed as “configured to” perform a task or tasks. In such contexts, the phrase “configured to” is used to connote structure by indicating that the units/circuits/components include structure (e.g., circuitry) that performs the task or tasks during operation. As such, the unit/circuit/component can be said to be configured to perform the task even when the specified unit/circuit/component is not currently operational (e.g., is not on). The units/circuits/components used with the “configured to” language include hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Reciting that a unit/circuit/component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. 112, sixth paragraph, for that unit/circuit/component. Additionally, “configured to” can include generic structure (e.g., generic circuitry) that is manipulated by software and/or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the task(s) at issue. “Configured to” may also include adapting a manufacturing process (e.g., a semiconductor fabrication facility) to fabricate devices (e.g., integrated circuits) that are adapted to implement or perform one or more tasks. 
     The foregoing description, for the purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the embodiments and its practical applications, to thereby enable others skilled in the art to best utilize the embodiments and various modifications as may be suited to the particular use contemplated. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.