Patent Publication Number: US-8996837-B1

Title: Providing multi-tenancy within a data storage apparatus

Description:
BACKGROUND 
     Data storage systems typically include one or more physical storage processors (SPs) accessing an array of disk drives and/or electronic flash drives. Each SP is connected to a network, such as the Internet and/or a storage area network (SAN), and receives transmissions over the network from host computing devices (“hosts”). The transmissions from the hosts include “IO requests,” also called “host IOs.” Some IO requests direct the SP to read data from an array, whereas other IO requests direct the SP to write data to the array. Also, some IO requests perform block-based data requests, where data are specified by LUN (Logical Unit Number) and offset values, whereas others perform file-based requests, where data are specified using file names and paths. Block-based IO requests typically conform to a block-based protocol, such as Fibre Channel or iSCSI (Internet SCSI, where SCSI is an acronym for Small Computer System Interface), for example. File-based IO requests typically conform to a file-based protocol, such as NFS (Network File System), CIFS (Common Internet File System), or SMB (Server Message Block), for example. 
     In some data storage systems, an SP may operate one or more virtual data movers. As is known, a virtual data mover is a logical grouping of file systems and servers that is managed by the SP and provides a separate context for managing host data stored on the array. A single SP may provide multiple virtual data movers for different users or groups. For example, a first virtual data mover may organize data for users in a first department of a company, whereas a second virtual data mover may organize data for users in a second department of the company. Each virtual data mover may include any number of host file systems for storing user data. As a virtual data mover requires additional storage to store more host data, the data storage system typically provides LUN slices to that virtual data mover from a pool of LUN slices which is shared among all of the virtual data movers of the data storage system, e.g., free LUN slices which have been reclaimed by the data storage system for reuse. 
     SUMMARY 
     Unfortunately, there are deficiencies to the above-described conventional approach to sharing LUN slices among all of the virtual data movers of a data storage system. For example, suppose that the finance department and the engineering department of the same company share the same data storage system. In this situation, LUN slices which may have been used by the finance department to store confidential financial data may be released back to the pool when no longer needed and then provided to the engineering department. Accordingly, such operation may present a data security concern. 
     It should be understood that some data storage systems could erase LUN slices prior to releasing them back to the pool (e.g., overwrite the LUN slices with zeroes). However, even in these situations, there is added overhead and there may still be the perception of risk. 
     Furthermore, since the LUN slices used by different departments of the company may reside on the same storage drives (e.g., the same flash memory drive, the same magnetic disk drive, etc.), all departments sharing the same storage drives are affected by any activities relating to these storage drives. For example, any storage drive upgrade or replacement must be coordinated with all departments sharing these storage drives, perhaps making the upgrade/replacement process more difficult to schedule and/or perform. Similarly, a failure of a particular storage drive may negatively affect both departments since both departments must now compete for access during a failover or recovery process. 
     In contrast to the above-described conventional approach which shares LUN slices among all of the virtual data movers of a data storage system, improved techniques are directed to establishing one-to-one relationships between slice pools and sets of virtual storage processors (VSPs) to provide multi-tenancy within a data storage apparatus. Here, the resources of the data storage apparatus are capable of being partitioned from the network down to the storage units to enable tenants to independently operate without intruding on each other and creating unnecessary risks. For example, two departments within the same company may utilize the same data storage system, but utilize their own slice pools. Moreover, such slice pools may be formed from separate groups of storage units thus freeing the departments from any storage unit interdependency. 
     One embodiment is directed to a method of providing multi-tenancy within a data storage apparatus. The method includes dividing, by processing circuitry, storage units of the data storage apparatus into multiple groups of storage units. The method further includes forming, by the processing circuitry, segregated slice pools from the multiple groups of storage units. Each segregated slice pool is formed from a different group of storage units. The method further includes allocating, by the processing circuitry, slices from the segregated slice pools to mutually exclusive sets of virtual storage processors (VSPs) on the data storage apparatus. Each mutually exclusive set of VSPs operates as a separate tenant of the data storage apparatus. 
     In some arrangements, allocating the slices from the segregated slice pools to the mutually exclusive sets of VSPs includes (i) reassigning slices from a first slice pool formed from a first group of storage units only to a first set of VSPs, and (ii) reassigning slices from a second slice pool formed from a second group of storage units only to a second set of VSPs. Such an arrangement prevents the slices from the first slice pool from being used by the second set of VSPs, and vice versa. 
     In some arrangements, the method further includes, prior to allocating the slices, appointing newly created VSPs on the data storage apparatus to the mutually exclusive sets of VSP. In these arrangements, each newly created VSP is appointed to exactly one of the mutually exclusive sets of VSPs. 
     In some arrangements, appointing the newly created VSPs includes appointing more than one VSP to a particular mutually exclusive set of VSPs to enable multiple VSPs of the particular mutually exclusive set of VSPs to share slices of the same slice pool. Accordingly, the slices of the same slice pool can be shared among more than VSP, but not shared with a VSP of a different set. 
     In some arrangements, appointing the newly created VSPs includes appointing exactly one VSP to each mutually exclusive set of VSPs to provide a one-to-one correspondence between VSP and slice pool. In these arrangements, only one VSP is allowed to access each slice pool. 
     In some arrangements, forming the segregated slice pools from the multiple groups of storage units includes creating the first slice pool from the first group of storage units, and creating the second slice pool from the second group of storage units. In these arrangements, at least one slice pool includes (i) a first tier of storage units providing a first data access speed level and (ii) a second tier of storage units providing a second data access speed level which is slower that the first data access speed level. Accordingly, different types of storage units can be used in the same slice pool to provide multiple storage tiers based on access speed. 
     In some arrangements, forming the segregated slice pools from the multiple groups of storage units includes creating slice pools from different RAID groups. For example, the first slice pool may be created from the first group of storage units, the first group of storage units being configured as a first redundant apparatus of independent disks (RAID) group. Likewise, the second slice pool may be created from the second group of storage units, the second group of storage units being configured as a second RAID group which is separate from the first RAID group, and so on. In these arrangements, each RAID group operates in accordance with a predefined RAID level. 
     In some arrangements, the method further includes steering host input/output (I/O) requests received from host applications to a particular set of VSPs which is allocated slices from a particular segregated slice pool formed from a particular group of storage units. Such operation maintains host data isolation from host I/O request receipt by the particular set of VSPs to host data storage within the particular group of storage units. Such an arrangement provides effective partitioning of host data from the network down to the storage units. 
     It should be understood that, in the cloud context, the electronic circuitry is formed by remote computer resources distributed over a network. Such a computing environment is capable of providing certain advantages such as enhanced fault tolerance, load balancing, processing flexibility, etc. 
     Other embodiments are directed to electronic systems and apparatus, processing circuits, computer program products, and so on. Some embodiments are directed to various methods, electronic components and circuitry which are involved in providing multi-tenancy within a data storage apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. In the accompanying drawings, 
         FIG. 1  is a block diagram showing an example data storage apparatus in an environment wherein improved techniques hereof may be practiced, the data storage apparatus including a storage processor having multiple virtualized storage processors (VSPs); 
         FIG. 2  is a block diagram showing example features of the front end of  FIG. 1  in additional detail; 
         FIG. 3  is a block diagram showing an example set of file systems of a VSP of  FIG. 1 ; 
         FIG. 4  is a table showing an example set of records stored in a configuration database that defines a VSP that can be run on the storage processor of  FIG. 1 ; 
         FIGS. 5A and 5B  are block diagrams showing example arrangements of virtualized storage processors; and 
         FIG. 6  is a flowchart showing an example process for managing host data using a VSP. 
         FIG. 7  is a block diagram illustrating how a LUN slice pool is formed from a set of Flare LUNs. 
         FIG. 8  is a block diagram of multi-tenant configuration which is supported by the data storage apparatus of  FIG. 1 . 
         FIG. 9  is a flowchart of a procedure which is performed by the data storage apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     Embodiments of the invention will now be described. It is understood that such embodiments are provided by way of example to illustrate various features and principles of the invention, and that the invention hereof is broader than the specific example embodiments disclosed. 
     An improved technique is directed to establishing one-to-one relationships between slice pools and sets of virtual storage processors (VSPs) to provide multi-tenancy within a data storage apparatus. Here, the resources of the data storage apparatus are capable of being partitioned from the network down to the storage units to enable tenants to independently operate without intruding on each other to prevent creation of unnecessary risks. For example, two departments within the same company may utilize the same data storage system, but utilize their own slice pools. Moreover, such slice pools may be formed from separate groups of storage units thus freeing the departments from any storage unit interdependency. 
     Data Storage System Details 
     In a typical virtual data mover arrangement, the SP has a root file system with mount points to which the host file systems of each virtual data mover are mounted. Thus, the SP and all its virtual data movers form a single, large directory and all share a common namespace. Hosts can access their virtual data mover-managed data by connecting to the SP over the network, logging on, and specifying paths relative to the SP&#39;s root where their data are kept. The typical arrangement thus requires hosts to access data of a virtual data mover using paths that are referenced to and dependent upon the root of the SP. 
     In addition, settings for prescribing virtual data mover operations are conventionally stored in the root file system of the SP. Many of these settings are global to all virtual data movers operating on the SP; others may be specific to particular virtual data movers. 
     Unfortunately, the intermingling of virtual data mover content within an SP&#39;s root file system impairs the ease of mobility and management of virtual data movers. For example, administrators wishing to move a virtual data mover (e.g., its file systems, settings, and servers) from one SP to another SP must typically perform many steps on a variety different data objects. File systems, server configurations, and other settings may need to be moved one at a time. Also, as the contents of different virtual data movers are often co-located, care must be taken to ensure that changes affecting one virtual data mover do not disrupt the operation of other virtual data movers. 
     In contrast with the conventional approach, an improved technique for managing host data in a data storage apparatus provides virtualized storage processors (VSPs) as substantially self-describing and independent entities. Each VSP has its own namespace, which is independent of the namespace of any other VSP. Each VSP also has its own network address. Hosts may thus access VSPs directly, without having to include path information relative to the SP on which the VSPs are operated. VSPs can thus be moved from one physical SP to another with little or no disruption to hosts, which may in many cases continue to access the VSPs on the new SPs using the same paths as were used to access the VSPs on the original SPs. 
     In some examples, each VSP includes within its namespace a configuration file system storing configuration settings for operating the VSP. These configuration settings include, for example, network interface settings and internal settings that describe the VSPs “personality,” i.e., the manner in which the VSP interacts on the network. By providing these settings as part of the VSP itself (e.g., within the file systems of the VSP), the VSP can be moved from one physical SP to another substantially as a unit. The increased independence of the VSP from its hosting SP promotes many aspects of VSP management, including, for example, migration, replication, failover, trespass, multi-tenancy, load balancing, and gateway support. 
     In some examples, the independence of VSPs is further promoted by storing data objects of VSPs in the form of respective files. These data objects may include, for example, file systems, LUNs, virtual storage volumes (vVols), and virtual machine disks (VMDKs). Each such file is part of a set of internal file systems of the data storage apparatus. Providing data objects in the form of files of a set of internal file systems promotes independence of VSPs and unifies management of file-based objects and block-based objects. 
     In accordance with improvements hereof, certain embodiments are directed to a method of managing host data on a data storage apparatus connected to a network. The method includes storing a network address and a set of host data objects accessible within a namespace of a virtualized storage processor (VSP) operated by a physical storage processor of the data storage apparatus. The namespace includes only names of objects that are specific to the VSP. The method further includes receiving, by the physical storage processor, a transmission over the network from a host computing device. The transmission is directed to a network address and includes an IO request designating a pathname to a host data object to be written or read. The method still further includes identifying the host data object designated by the IO request by (i) matching the network address to which the transmission is directed with the network address stored for the VSP, to identify the VSP as the recipient of the IO request, and (ii) locating the host data object within the namespace of the VSP using the pathname. The IO request is then processed to complete the requested read or write operation on the identified host data object. 
     Other embodiments are directed to computerized apparatus and computer program products. Some embodiments involve activity that is performed at a single location, while other embodiments involve activity that is distributed over a computerized environment (e.g., over a network). 
     An improved technique for managing host data in a data storage apparatus provides virtualized storage processors (VSPs) as substantially self-describing and independent constructs. 
       FIG. 1  shows an example environment  100  in which embodiments of the improved technique hereof can be practiced. Here, multiple host computing devices (“hosts”)  110 ( 1 ) through  110 (N), access a data storage apparatus  116  over a network  114 . The data storage apparatus  116  includes a physical storage processor, or “SP,”  120  and storage  180 . The storage  180  is provided, for example, in the form of hard disk drives and/or electronic flash drives. Although not shown in  FIG. 1 , the data storage apparatus  116  may include multiple SPs like the SP  120 . For instance, multiple SPs may be provided as circuit board assemblies, or “blades,” which plug into a chassis that encloses and cools the SPs. The chassis has a backplane for interconnecting the SPs, and additional connections may be made among SPs using cables. It is understood, however, that no particular hardware configuration is required, as any number of SPs (including a single one) can be provided and the SP  120  can be any type of computing device capable of processing host IOs. 
     The network  114  can be any type of network, such as, for example, a storage area network (SAN), local area network (LAN), wide area network (WAN), the Internet, some other type of network, and/or any combination thereof. In an example, the hosts  110 ( 1 -N) connect to the SP  120  using various technologies, such as Fibre Channel, iSCSI, NFS, SMB 3.0, and CIFS, for example. Any number of hosts  110 ( 1 -N) may be provided, using any of the above protocols, some subset thereof, or other protocols besides those shown. As is known, Fibre Channel and iSCSI are block-based protocols, whereas NFS, SMB 3.0, and CIFS are file-based protocols. The SP  120  is configured to receive 10 requests  112 ( 1 -N) in transmissions from the hosts  110 ( 1 -N) according to both block-based and file-based protocols and to respond to such IO requests  112 ( 1 -N) by reading or writing the storage  180 . 
     The SP  120  is seen to include one or more communication interfaces  122 , control circuitry (e.g., a set of processors  124 ), and memory  130 . The communication interfaces  122  include, for example, adapters, such as SCSI target adapters and network interface adapters, for converting electronic and/or optical signals received from the network  114  to electronic form for use by the SP  120 . The set of processors  124  includes one or more processing chips and/or assemblies. In a particular example, the set of processors  124  includes numerous multi-core CPUs. The memory  130  includes both volatile memory (e.g., RAM), and non-volatile memory, such as one or more ROMs, disk drives, solid state drives (SSDs), and the like. The set of processors  124  and the memory  130  are constructed and arranged to carry out various methods and functions as described herein. Also, the memory  130  includes a variety of software constructs realized in the form of executable instructions. When the executable instructions are run by the set of processors  124 , the set of processors  124  are caused to carry out the operations of the software constructs. Although certain software constructs are specifically shown and described, it is understood that the memory  130  typically includes many other software constructs, which are not shown, such as various applications, processes, and daemons. 
     As shown, the memory  130  includes an operating system  134 , such as Unix, Linux, or Windows™, for example. The operating system  134  includes a kernel  136 . The memory  130  is further seen to include a container  132 . In an example, the container  132  is a software process that provides an isolated userspace execution context within the operating system  134 . In various examples, the memory  130  may include multiple containers like the container  132 , with each container providing its own isolated userspace instance. Although containers provide isolated environments that do not directly interact (and thus promote fault containment), different containers can be run on the same kernel  136  and can communicate with one another using inter-process communication (IPC) mediated by the kernel  136 . Containers are well-known features of Unix, Linux, and other operating systems. 
     In the example of  FIG. 1 , only a single container  132  is shown. Running within the container  132  is an IO stack  140  and multiple virtualized storage processors (VSPs)  150 ( 1 - 3 ). The IO stack  140  provides an execution path for host IOs (e.g.,  112 ( 1 -N)) and includes a front end  142  and a back end  144 . The VSPs  150 ( 1 - 3 ) each run within the container  132  and provide a separate context for managing host data. In an example, each VSP manages a respective set of host file systems and/or other data objects and uses servers and settings for communicating over the network  114  with its own individual network identity. Although three VSPs are shown, it is understood that the SP  120  may include as few as one VSP or as many VSPs as the computing resources of the SP  120  and storage resources of the storage  180  allow. 
     Although the VSPs  150 ( 1 - 3 ) each present an independent and distinct identity, it is evident that the VSPs  150 ( 1 - 3 ) are not, in this example, implemented as independent virtual machines. Rather, all VSPs  150 ( 1 - 3 ) operate in userspace and employ the same kernel  136  of the SP  120 . Although it is possible to implement the VSPs  150 ( 1 - 3 ) as independent virtual machines (each including a virtualized kernel), it has been observed that VSPs perform faster when the kernel  136  is not virtualized. 
     Also, it is observed that the VSPs  150 ( 1 - 3 ) all run within the container  132 , i.e., within a single userspace instance. Again, the arrangement shown reflects a deliberate design choice aimed at optimizing VSP performance. It is understood, though, that alternative implementations could provide different VSPs in different containers, or could be provided without containers at all. 
     The memory  130  is further seen to store a configuration database  170 . The configuration database  170  stores system configuration information, including settings related to the VSPs  150 ( 1 - 3 ) and their data objects. In other implementations, the configuration database  170  is stored elsewhere in the data storage apparatus  116 , such as on a disk drive separate from the SP  120  but accessible to the SP  120 , e.g., over a backplane or network. 
     In operation, the hosts  110 ( 1 -N) issue IO requests  112 ( 1 -N) to the data storage apparatus  116 . The IO requests  112 ( 1 -N) may include both block-based requests and file-based requests. The SP  120  receives the IO requests  112 ( 1 -N) at the communication interfaces  122  and passes the IO requests to the IO stack  140  for further processing. 
     At the front end  142  of the IO stack  140 , processing includes associating each of the IO requests  112 ( 1 -N) with a particular one of the VSPs  150 ( 1 - 3 ). In an example, each VSP stores a network address (e.g., an IP address) in a designated location within its file systems. The front end  142  identifies the network address to which each IO request is directed and matches that address with one of the network addresses stored with the VSPs  150 ( 1 - 3 ). The front end  142  thus uses the network address to which each IO request is sent to identify the VSP to which the IO request is directed. Further processing of the IO request is then associated (e.g., tagged) with an identifier of the matching VSP, such that the IO request is processed within a particular VSP context. Any data logging, metrics collection, fault reporting, or messages generated while the IO request is being processed are stored with the associated VSP (e.g., in a file system dedicated to the VSP). Also, any path information provided with the IO request (e.g., to a particular directory and file name) is interpreted within the namespace of the identified VSP. 
     Processing within the front end  142  may further include caching data provided with any write IOs and mapping host data objects (e.g., host file systems, LUNs, vVols, VMDKs, etc.) to underlying files stored in a set of internal file systems. Host IO requests received for reading and writing both file systems and LUNs are thus converted to reads and writes of respective files. The IO requests then propagate to the back end  144 , where commands are executed for reading and/or writing the physical storage  180 . 
     In an example, processing through the IO stack  140  is performed by a set of threads maintained by the SP  120  in a set of thread pools. When an IO request is received, a thread is selected from the set of thread pools. The IO request is tagged with a VSP identifier, and the selected thread runs with the context of the identified VSP. Typically, multiple threads from different thread pools contribute to the processing of each IO request (there are many processing layers). Multiple threads from the thread pools can process multiple IO requests simultaneously, i.e., in parallel, on the data objects of any one VSP or multiple VSPs. 
     Although  FIG. 1  shows the front end  142  and the back end  144  together in an “integrated” form, the front end  142  and back end  144  may alternatively be provided on separate SPs. For example, the IO stack  140  may be implemented in a “modular” arrangement, with the front end  142  on one SP and the back end  144  on another SP. The IO stack  140  may further be implemented in a “gateway” arrangement, with multiple SPs running respective front ends  142  and with a back end provided within a separate storage array. The back end  144  performs processing that is similar to processing natively included in many block-based storage arrays. Multiple front ends  142  can thus connect to such arrays without the need for providing separate back ends. In all arrangements, processing through both the front end  142  and back end  144  is preferably tagged with the particular VSP context such that the processing remains VSP-aware. 
       FIG. 2  shows portions of the front end  142  in additional detail. Here, and describing the architecture generally without regard to any particular VSP, it is seen that a set of lower-deck file systems  202  represents LUNs and host file systems in the form of files. Any number of lower-deck file systems  202  may be provided. In one arrangement, a single lower-deck file system may include, as files, any number of LUNs and/or host file systems, as well as their snaps (i.e., point-in-time copies). In another arrangement, a different lower-deck file system is provided for each primary object to be stored, e.g., for each LUN and for each host file system. Additional arrangements provide groups of host file systems and/or groups of LUNs together in a single lower deck file system. The lower-deck file system for any object may include a file storing the object itself, as well as files storing any snaps of the object. Each lower-deck file system  202  has an inode table (e.g.,  232 ,  242 ), which provides a unique inode for each file stored in the lower-deck file system. The inode table of each lower-deck file system stores properties of each file in the respective lower-deck file system, such as ownership and block locations at which the file&#39;s data are stored. Lower-deck file systems are built upon storage elements managed by a storage pool  204 . 
     The storage pool  204  organizes elements of the storage  180  in the form of slices. A “slice” is an increment of storage space, such as 256 MB in size, which is obtained from the storage  180 . The pool  204  may allocate slices to lower-deck file systems  202  for use in storing their files. The pool  204  may also deallocate slices from lower-deck file systems  202  if the storage provided by the slices is no longer required. In an example, the storage pool  204  creates slices by accessing RAID groups formed from the storage  180 , dividing the RAID groups into FLUs (Flare LUNs), and further dividing the FLU&#39;s into slices. 
     Continuing with reference to the example shown in  FIG. 2 , a user object layer  206  includes a representation of a LUN  210  and of an HFS (host file system)  212 , and a mapping layer  208  includes a LUN-to-file mapping  220  and an HFS-to-file mapping  222 . The LUN-to-file mapping  220  maps the LUN  210  to a first file F1 ( 236 ), and the HFS-to-file mapping  222  maps the HFS  212  to a second file F2 ( 246 ). Through the LUN-to-file mapping  220 , any set of blocks identified in the LUN  210  by a host IO request is mapped to a corresponding set of blocks within the first file  236 . Similarly, through the HFS-to-file mapping  222 , any file or directory of the HFS  212  is mapped to a corresponding set of blocks within the second file  246 . The HFS  212  is also referred to herein as an “upper-deck file system,” which is distinguished from the lower-deck file systems  202 , which are for internal use. 
     In this example, a first lower-deck file system  230  includes the first file  236  and a second lower-deck file system  240  includes the second file  246 . Each of the lower-deck file systems  230  and  240  includes an inode table ( 232  and  242 , respectively). The inode tables  232  and  242  provide information about files in respective lower-deck file systems in the form of inodes. For example, the inode table  232  of the first lower-deck file system  230  includes an inode  234 , which provides file-specific information about the first file  236 . Similarly, the inode table  242  of the second lower-deck file system  240  includes an inode  244 , which provides file-specific information about the second file  246 . The information stored in each inode includes location information (e.g., block locations) where the respective file is stored, and may thus be accessed as metadata to identify the locations of the files  236  and  246  in the storage  180 . 
     Although a single file is shown for each of the lower-deck file systems  230  and  240 , it is understood that each of the lower-deck file systems  230  and  240  may include any number of files, each with its own entry in the respective inode table. In one example, each lower-deck file system stores not only the file F1 or F2 for the LUN  210  or HFS  212 , but also snaps of those objects. For instance, the first lower-deck file system  230  stores the first file  236  along with a different file for every snap of the LUN  210 . Similarly, the second lower-deck file system  240  stores the second file  246  along with a different file for every snap of the HFS  212 . 
     As shown, a set of slices  260  is allocated by the storage pool  204  for storing the first file  236  and the second file  246 . In the example shown, slices S1 through S4 are used for storing the first file  236 , and slices S5 through S7 are used for storing the second file  246 . The data that make up the LUN  210  are thus stored in the slices S1 through S4, whereas the data that make up the HFS  212  are stored in the slices S5 through S7. 
     In some examples, each of the lower-deck file systems  230  and  240  is associated with a respective volume, such as a sparse LUN. Sparse LUNs provide an additional layer of mapping between the lower-deck file systems  202  and the pool  204  and allow the lower-deck file systems to operate as file systems normally do, by accessing underlying volumes. Additional details about sparse LUNs and their relation to lower-deck file systems may be found in U.S. Pat. No. 7,631,155, which is hereby incorporated by reference in its entirety. The incorporated patent uses the term “container file system” to refer to a construct similar to the lower-deck file system disclosed herein. 
     Although the example of  FIG. 2  shows storage of a LUN  210  and a host file system  212  in respective lower-deck file systems  230  and  240 , it is understood that other data objects may be stored in one or more lower-deck file systems in a similar manner. These may include, for example, file-based vVols, block-based vVols, and VMDKs. 
       FIG. 3  shows an example set of components of the data storage apparatus  116  that are associated with a particular VSP  300  (i.e., any of the VSPs  150 ( 1 - 3 )). The components shown in  FIG. 3  include components that are managed in the context of the VSP  300  and components that form the “personality” of the VSP  300 . These components may be referred to herein as “included” within the VSP  300 , by which it is meant that the components are associated with the VSP  300  within the data storage apparatus  116  and are not associated with any other VSP. It is thus seen that the VSP  300  “includes” a number of lower-deck file systems hosting various host data objects, as well as internal data objects. 
     For example, the VSP  300  includes a first lower-deck file system  310  and a second lower-deck file system  320 . The first lower-deck file system  310  includes a file FA, which provides a file representation of a first host file system  312 . Similarly, the second lower-deck file system  320  includes a file FB, which provides a file representation of a second host file system  322 . The host file systems  312  and  322  are upper-deck file systems, which may be made available to hosts  110 ( 1 -N) for storing file-based host data. HFS-to-file mappings, like the HFS-to-file mapping  222 , are understood to be present (although not shown in  FIG. 3 ) for expressing the files FA and FB in the form of upper-deck file systems. Although only two host file systems  312  and  322  are shown, it is understood that the VSP  300  may include any number of host file systems. In an example, a different lower-deck file system is provided for each host file system. The lower-deck file system stores the file representation of the host file system, and, if snaps are turned on, any snaps of the host file system. In a similar manner to that described in connection with  FIG. 2 , each of the lower-deck file systems  310  and  320  includes a respective inode table, allowing the files FA and FB and their snaps to be indexed within the respective lower-deck file systems and accessed within the storage  180 . 
     In some examples, the VSP  300  also includes one or more lower-deck file systems for storing file representations of LUNs. For example, a lower-deck file system  330  stores a file FC, which provides a file representation of a LUN  332 . A LUN-to-file mapping (not shown but similar to the mapping  320 ) expresses the file FC in the form of a LUN, which may be made available to hosts  110 ( 1 -N) for storing block-based host data. In an example, the lower-deck file system  330  stores not only the file FC, but also snaps thereof, and includes an inode table in essentially the manner described above. 
     The VSP  300  further also includes a lower-deck file system  340 . In an example, the lower-deck file system  340  stores file representations FD and FE of two internal file systems of the VSP  300 —a root file system  342  and a configuration file system  344 . In an alternative arrangement, the files FD and FE are provided in different lower-deck file systems. In an example, the lower-deck file system  340  also stores snaps of the files FD and FE, and files are accessed within the lower-deck file system  340  via file system-to-file mappings and using an inode table, substantially as described above. 
     In an example, the root file system  342  has a root directory, designated with the slash (“/”), and sub-directories as indicated. Any number of sub-directories may be provided within the root file system in any suitable arrangement with any suitable file structure; the example shown is merely illustrative. As indicated, one sub-directory (“Local”) stores, for example, within constituent files, information about the local environment of the SP, such as local IP sub-net information, geographical location, and so forth. Another sub-directory (“Rep”) stores replication information, such as information related to any ongoing replication sessions. Another sub-directory (“Cmd Svc”) stores command service information, and yet another sub-directory (“MPs”) stores mount points. 
     In the example shown, the directory “MPs” of the root file system  342  provides mount points (e.g., directories) on which file systems are mounted. For example, the host file systems  312  and  322  are respectively mounted on mount points MP1 and MP2, and the configuration file system  344  is mounted on the mount point MP3. In an example, establishment of the mount points MP1-MP3 and execution of the mounting operations for mounting the file systems  312 ,  322 ,  344  onto the mount points MP1-MP4 are provided in a batch file stored in the configuration file system  344  (e.g., in Host Objects). It is understood that additional mount points may be provided for accommodating additional file systems. 
     The root file system  342  has a namespace, which includes the names of the root directory, sub-directories, and files that belong to the root file system  342 . The file systems  312 ,  322 , and  344  also each have respective namespaces. The act of mounting the file systems  312 ,  322 , and  344  onto the mount points MP1, MP2, and MP3 of the root file system  342  serves to join the namespace of each of the file systems  312 ,  322 , and  344  with the namespace of the root file system  342 , to form a single namespace that encompasses all the file systems  312 ,  322 ,  342 , and  344 . This namespace is specific to the VSP  300  and is independent of namespaces of any other VSPs. 
     Also, it is understood that the LUN  332  is also made available to hosts  110   a - n  through the VSP  300 . For example, hosts  110   a - n  can send read and write IO requests to the LUN  332  (e.g., via Fibre Channel and/or iSCSI commands) and the SP  120  services the requests for the VSP  300 , e.g., by operating threads tagged with the context of the VSP  300 . Although  FIG. 3  shows both the LUN  322  and the host file systems  312  and  322  together in a single VSP  300 , other examples may provide separate VSPs for LUNs and for file systems. 
     Although the VSP  300  is seen to include file systems and LUNs, other host objects may be included, as well. These include, for example, file-based vVols, block-based vVols, and VMDKs. Such host objects may be provided as file representations in lower-deck file systems and made available to hosts  110   a - n.    
     As its name suggests, the configuration file system  344  stores configuration settings for the VSP  300 . These settings include settings for establishing the “personality” of the VSP  300 , i.e., the manner in which the VSP  300  interacts over the network  114 . Although the configuration file system  344  is shown with a particular directory structure, it is understood that any suitable directory structure can be used. In an example, the configuration file system  344  stores the following elements:
         IF Config. Interface configuration settings of any network interface used for processing IO requests and tagged with a context of the VSP  300 . IF Config includes the IP address of the VSP, as well as related network information, such as sub-masks and related IP information.   CIFS. Configuration settings and names of one or more CIFS servers used in the context of the VSP  300 . The CIFS servers manage IO requests provided in the CIFS protocol. By including the CIFS configuration within the configuration file system  344 , the CIFS configuration becomes part of the VSP  300  itself and remains with the VSP  300  even as the VSP  300  is moved from one SP to another SP. This per-VSP configuration of CIFS also permits each VSP to have its own customized CIFS settings, which may be different from the settings of CIFS servers used by other VSPs.   NFS. Configuration settings and names of one or more NFS servers used in the context of the VSP  300 . The NFS servers manage IO requests provided in the NFS protocol. By including the NFS configuration within the configuration file system  344 , the NFS configuration becomes part of the VSP  300  itself and remains with the VSP  300  even as the VSP  300  is moved from one SP to another SP. This per-VSP configuration of NFS also permits each VSP to have its own customized NFS settings, which may be different from the settings of NFS servers used by other VSPs.   Exports. NFS exports, CIFS shares, and the like for all supported protocols. For security and management of host access, users are typically given access only to specified resources mounted to the root file system  342 , e.g., host file systems, sub-directories of those file systems, and/or particular LUNs. Access to these resources is provided by performing explicit export/share operations, which expose entry points to the resources for host access. In an example, these export/share operations are included within one or more batch files, which may be executed when the VSP  300  is started. Exports are typically VSP-specific, and depend upon the particular data being hosted and the access required.   CAVA/NDMP: CAVA (Celerra Anti-Virus Agent) configuration file, including location of external server for performing virus checking operations. NDMP (Network Data Management Protocol) provides backup configuration information. CAVA and NDMP settings are configurable on a per-VSP basis.   NIS/DNS/LDAP: Local configurations and locations of external servers for providing resolution of IP addresses. NIS (Network Information Service), DNS (Directory Name System), and LDAP (Lightweight Directory Access Protocol) settings are configurable on a per-VSP basis. The DNS configuration stores local host name and domain name of the VSP  300 , as well as the location of a DNS server for resolving host names.   Host Objects: Identifiers for all host file systems (e.g.,  312  and  322 ), LUNs (e.g., LUN  332 ), and other host objects included within the VSP  300 . Host objects may also include batch files and/or lists of instructions for establishing mount points in the root file system  342  and for mounting the host file system(s) and LUN(s) to the mount points.   Parameters: Low-level settings (e.g., registry settings) for configuring VSP  300 . These include cache settings and settings for specifying a maximum number of threads running on the SP  120  that may be used to service IO requests within the context of the VSP  300 . Parameters are configurable on a per-VSP basis.   Statistics: Metrics, log files, and other information pertaining to activities within the context of the VSP  300 . Statistics are updated as they accumulate.
 
Many configuration settings are established at startup of the VSP  300 . Some configuration settings are updated as the VSP  300  is operated. The configuration file system  344  preferably does not store host data.
       

     Although  FIG. 3  has been shown and described with reference to a particular VSP  300 , it is understood that all of the VSPs  150 ( 1 - 3 ) may include a root file system, a configuration file system, and at least one host file system or LUN, substantially as shown. Particular host objects and configuration settings differ, however, from one VSP to another. 
     By storing the configuration settings of VSPs within the file systems of the VSPs themselves and providing a unique namespace for each VSP, VSPs are made to be highly independent, both of other VSPs and of the particular SPs on which they are provided. For example, migrating a VSP from a first data storage system to a second data storage system involves copying its lower-deck file systems (or some subset thereof) from a source SP on the first data storage system to a target SP on the second, starting the VSP&#39;s servers on the target SP in accordance with the configuration settings, and resuming operation on the target SP. As the paths for accessing data objects on VSPs are not rooted to the SPs on which they are run, hosts may often continue to access migrated VSPs using VSPs using the same instructions as were used prior to moving the VSPs. Similar benefits can be enjoyed when moving a VSP from one SP to another SP in the same data storage system. To move a VSP from a first SP to a second SP, The VSP need merely be shut down (i.e., have its servers stopped) on the first SP and resumed (i.e., have its servers started up again) on the second SP. 
       FIG. 4  shows an example record  400  of the configuration database  170 , which are used to define a particular VSP having a VSP identifier (ID)  410 . The VSP ID  410  may identify one of the VSPs  150 ( 1 - 3 ) or some other VSP of the data storage apparatus  116 . The record  400  specifies, for example, an owning SP (physical storage processor), authentication, and identifiers of the data objects associated with the listed VSP. The data object identifiers include identifiers of the root file system, configuration file system, and various host file systems (or other host objects) that may be accessed in the context of the listed VSP. The record  400  may also identify the lower-deck file system used to store each data object. The record  400  may further specify host interfaces that specify IO protocols that the listed VSP is equipped to handle. 
     Although  FIG. 4  shows only a single record  400  for a single VSP, it is understood that the configuration database  170  may store records, like the record  400 , for any number of VSPs, including all VSPs of the data storage apparatus  116 . During start-up of the data storage apparatus  116 , or at some other time, a computing device of the data storage apparatus  116  reads the configuration database  170  and launches a particular VSP or a group of VSPs on the identified SPs. As a VSP is starting, the SP that owns the VSP reads the configuration settings of the configuration file system  344  to configure the various servers of the VSP and to initialize its communication protocols. The VSP may then be operated on the identified SP, i.e., the SP may then be operated with the particular VSP&#39;s context. 
     It is understood that VSPs  150 ( 1 - 3 ) operate in connection with the front end  142  of the IO stack  140 . The VSPs  150 ( 1 - 3 ) thus remain co-located with their respective front ends  142  in modular and gateway arrangements. 
       FIGS. 5A and 5B  show two different example arrangements of VSPs. In  FIG. 5A , the VSPs  150 ( 1 - 3 ) access the storage pool  204 . Thus, the lower-deck file systems of the VSPs  150 ( 1 - 3 ) all derive the slices needed to store their underlying file systems and other data objects from the pool  204 . In  FIG. 5B , multiple storage pools  550 ( 1 - 3 ) are provided, one for each of the VSPs  150 ( 1 - 3 ), respectively. Providing different pools for respective VSPs promotes data isolation among the VSPs, and may be better suited for applications involving multiple tenants in which each tenant&#39;s data must be kept separate from the data of other tenants. 
       FIG. 6  shows an example method  600  for managing host data on a data storage apparatus connected to a network. The method  600  that may be carried out in connection with the data storage apparatus  116 . The method  600  is typically performed by the software constructs, described in connection with  FIGS. 1-3 , which reside in the memory  130  of the storage processor  120  and are run by the set of processors  124 . The various acts of the method  600  may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in orders different from those illustrated, which may include performing some acts simultaneously, even though the acts are shown as sequential in the illustrated embodiments. 
     At step  610 , a network address and a set of host data objects are stored in a data storage apparatus. The set of host data objects are accessible within a namespace of a virtualized storage processor (VSP) operated by a physical storage processor of the data storage apparatus. The namespace includes only names of objects that are specific to the VSP. For example, an IP address of the VSP  300  is stored in a file of a directory of the configuration file system  344 . The VSP  300  runs on the SP  120  of the data storage apparatus  116 . A set of host objects, including host file systems  312  and  322 , and LUN  332 , are also stored in the data storage apparatus  116 . These host objects are made accessible within the namespace of the VSP  300  by mounting these data objects to mount points MP1-MP4 within the root file system  342  and thus merging their namespaces with that of the root file system  342 . The resulting merged namespace includes only names of objects that are specific to the VSP  300 . 
     At step  612 , a transmission is received by the physical storage processor over the network from a host computing device. The transmission is directed to a network address and includes an IO request designating a pathname to a host data object to be written or read. For example, the SP  120  receives a transmission over the network  114  from one of the hosts  110 ( 1 -N). The transmission is directed to a particular IP address and includes an IO request (e.g., one of  112 ( 1 -N)). The IO request designates a location of a host data object to be written or read (e.g., a pathname for a file-based object or a block designation for a block-based object). The location may point to any of the host file systems  312  or  322 , to the LUN  332 , or to any file or offset range accessible through the host file systems  312  or  322  or the LUN  332 , respectively. The location may also point to a vVol or VMDK, for example, or to any other object which is part of the namespace of the VSP  300 . 
     At step  614 , the host data object designated by the IO request is identified by (i) matching the network address to which the transmission is directed with the network address stored for the VSP, to identify the VSP as the recipient of the IO request, and (ii) locating the host data object within the namespace of the VSP using the pathname. For example, each of the VSPs  150 ( 1 - 3 ) stores an IP address in its configuration file system  344 . When an IO request is received, an interface running within the front end  142  of the IO stack  140  checks the IP address to which the IO request is directed and matches that IP address with one of the IP addresses stored for the VSPs  150 ( 1 - 3 ). The VSP whose IP address matches the IP address to which the IO request is directed is identified as the recipient of the IO request. The IO request arrives to the SP  120  with a pathname to the host data object to be accessed. The front end  142  looks up the designated pathname within the identified VSP to identify the particular data object to which the IO request is directed. 
     At step  616 , the IO request is processed to complete the requested read or write operation on the identified host data object. For example, the front end  142  and the back end  144  process the IO request to perform an actual read or write to the designated host data object on the storage  180 . 
     An improved technique has been described for managing host data in a data storage apparatus. The technique provides virtualized storage processors (VSPs) as substantially self-describing and independent entities. Each VSP has its own namespace, which is independent of the namespace of any other VSP. Each VSP also has its own network address. Hosts may thus access VSPs directly, without having to include path information relative to the SP on which the VSP is operated. VSPs can thus be moved from one physical SP to another with little or no disruption to hosts, which may continue to access the VSPs on the new SPs using the same paths as were used when the VSPs were running on the original SPs. 
     As used throughout this document, the words “comprising,” “including,” and “having” are intended to set forth certain items, steps, elements, or aspects in an open-ended fashion. Also, and unless explicitly indicated to the contrary, the word “set” as used herein indicates one or more of something. Although certain embodiments are disclosed herein, it is understood that these are provided by way of example only and the invention is not limited to these particular embodiments. 
     Having described certain embodiments, numerous alternative embodiments or variations can be made. For example, embodiments have been shown and described in which host file systems, LUNs, vVols, VMDKs, and the like are provided in the form of files of underlying lower-deck file systems. Although this arrangement provides advantages for simplifying management of VSPs and for unifying block-based and file-based operations, the use of lower-deck file systems is merely an example. Indeed, host file systems, LUNs, vVols, VMDKs, and the like may be provided for VSPs in any suitable way. 
     Also, although the VSPs  150 ( 1 - 3 ) are shown and described as userspace constructs that run within the container  132 , this is also merely an example. Alternatively, different VSPs may be provided in separate virtual machines running on the SP  120 . For example, the SP  120  is equipped with a hypervisor and a virtual memory manager, and each VSP runs in a virtual machine having a virtualized operating system. 
     Also, the improvements or portions thereof may be embodied as a non-transient computer-readable storage medium, such as a magnetic disk, magnetic tape, compact disk, DVD, optical disk, flash memory, Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA), and the like (shown by way of example as medium  650  in  FIG. 6 ). Multiple computer-readable media may be used. The medium (or media) may be encoded with instructions which, when executed on one or more computers or other processors, implement the various methods described herein. Such medium (or media) may be considered an article of manufacture or a machine, and may be transportable from one machine to another. 
     VSP Multi-Tenancy 
       FIG. 7  shows how a storage pool  204  of slices  250  of the data storage apparatus  116  is formed from a set of Flare LUNs. In particular, each Flare LUN includes multiple storage units which are configured into RAID groups operating in accordance with a predefine RAID level (e.g., RAID level 5, RAID level 6, RAID level 10, etc.). The RAID groups are then divided into LUNs and LUN slices  250  which are then supplied to the pool  204 . 
     By way of example only, the storage pool  204  is formed of slices  250  from different types of storage units or HDDs to provide multiple storage tiers based on access speed. In particular, a tier of flash drives forms a first tier of storage. Additionally, a tier of fast magnetic drives forms a second tier of storage. Furthermore, a tier of slow magnetic drives forms a third tier of storage. Accordingly, the storage pool  204  includes slices  250  from an assortment of different types of storage. 
       FIG. 8  shows a multi-tenant configuration  800  which is supported by the data storage apparatus  116  (also see  FIGS. 5A and 5B ). As shown in  FIG. 8 , a first set  802 (A) of VSPs  150 (A)( 1 ),  150 (A)( 2 ), . . . accesses storage pool  204 (A) of slices  250 . Likewise, a second set  802 (B) of VSPs  150 (B)( 1 ),  150 (B)( 2 ), . . . accesses storage pool  204 (B), and so on. The storage pools  204 (A),  204 (B), . . . (collectively, storage pools  204 ) are segregated in that they do not share slices  250 . Furthermore, the storage pools  204  do not share storage units. 
     It should be understood that, in contrast to a conventional approach which shares LUN slices among all of the virtual data movers of a data storage system, the configuration  800  establishes one-to-one relationships between slice pools  204  and sets  802  of VSPs  150  to provide multi-tenancy within the data storage apparatus  116 . That is, the resources of the data storage apparatus  116  are partitioned (see dashed line  804  in  FIG. 8 ) to enable tenants to independently operate without intruding on each other and creating unnecessary risks. Each tenant is a mutually exclusive (i.e., non-overlapping) set  802  of VSPs  150 . For example, a finance department and an engineering department within the same company may utilize the same data storage apparatus  116 , but utilize their own slice pools  204 . 
     It should be further understood that establishing multiple tenants may occur at setup time (e.g., during an initial setup phase of the data storage apparatus  116 , as a new VSP  150  is added, and so on). In some arrangements, each set  802  of VSPs  150  is permitting to include more than one VSP  150  (e.g., see  FIGS. 5A and 8 ), i.e., VSPs  150  of the same set  802  share slices  250  of the same slice pool  204 . In other arrangements, each set  802  of VSPs is permitted to include exactly one (or at most one) VSP  150  to provide a one-to-one correspondence between VSP  150  and slice pool  204 . 
       FIG. 9  shows a flowchart of a procedure  900  which is performed by the data storage apparatus  116  to provide multi-tenancy within the data storage apparatus  116 . At  902 , the data storage apparatus  116  divides storage units of the data storage apparatus  116  into multiple groups of storage units. In particular, as shown in  FIGS. 7 and 8 , each group is capable of including different types of storage units (e.g., flash drives, fast magnetic drives, slow magnetic drives, etc.) thus enabling storage of host data based on access criteria (e.g., placing the more frequently accessed host data on slices  250  of the faster storage units). 
     At  904 , the data storage apparatus  116  forms segregated slice pools  204  from the multiple groups of storage units. Each segregated slice pool  204  is formed from a different group of storage units (also see  FIGS. 7 and 8 ). 
     At  906 , the data storage apparatus  116  allocates slices  250  from the segregated storage pools  204  to mutually exclusive sets  802  of VSPs  150  on the data storage apparatus  116 , and each mutually exclusive set  802  of VSPs  150  operates as a separate tenant of the data storage apparatus  116 . It should be understood that such allocation involves reuse of pool slices  250  but only by the same set of  802  of VSPs  150 . 
     As described above, improved techniques are directed to establishing one-to-one relationships between slice pools  204  and sets  802  of VSPs  150  to provide multi-tenancy within a data storage apparatus  116 . Here, the resources of the data storage apparatus  116  are capable of being partitioned from the network down to the storage units to enable tenants to independently operate without intruding on each other and creating unnecessary risks. For example, multiple departments within the same company may utilize the same data storage apparatus  116 , but utilize their own storage pools  204 . Moreover, such storage pools  204  may be formed from separate groups of storage units thus freeing the departments from any storage unit interdependency. 
     While various embodiments of the present disclosure have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims. 
     Further, although features are shown and described with reference to particular embodiments hereof, such features may be included in any of the disclosed embodiments and their variants. Thus, it is understood that features disclosed in connection with any embodiment can be included as variants of any other embodiment, whether such inclusion is made explicit herein or not. Those skilled in the art will therefore understand that various changes in form and detail may be made to the embodiments disclosed herein without departing from the scope of the disclosure. Such modifications and enhancements are intended to belong to various embodiments of the disclosure.