Patent Publication Number: US-2023143598-A1

Title: In-place data recovery

Description:
CROSS REFERENCE 
     The present Application for Patent is a continuation of U.S. patent application Ser. No. 17/214,147 by MEADOWCROFT et al., entitled “IN-PLACE DATA RECOVERY,” filed Mar. 26, 2021, assigned to the assignee hereof, and expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     The volume and complexity of data that is collected, analyzed and stored is increasing rapidly over time. The computer infrastructure used to handle this data is also becoming more complex, with more processing power and more portability. As a result, data management and storage are becoming increasingly important. Significant issues with these processes include data loss or damage during transfer as well as high workload latency caused by transferring a large amount of backup data (e.g., a full snapshot) needed for data recovery. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Some embodiments are illustrated by way of example and not limited to the views of the accompanying drawing: 
         FIG.  1    is a block diagram depicting one embodiment of a networked computing environment in which the disclosed technology may be practiced, according to some embodiments. 
         FIG.  2    is a block diagram depicting one embodiment of the server of  FIG.  1   , according to some embodiments. 
         FIG.  3    is a block diagram depicting one embodiment of the storage appliance of  FIG.  1   , according to some embodiments. 
         FIG.  4    is a diagram showing an example cluster of a distributed decentralized database, according to some embodiments. 
         FIG.  5    depicts a flowchart indicating example in-place virtual machine recovery operations in a method, according to some embodiments. 
         FIG.  6    depicts a flowchart indicating example in-place virtual machine recovery operations in a method, according to some embodiments. 
         FIG.  7    depicts a block diagram illustrating a disk section of a virtual disk associated with a virtual machine, according to some embodiments. 
         FIG.  8    depicts a block diagram illustrating an architecture of software, according to some embodiments. 
         FIG.  9    illustrates a diagrammatic representation of a machine in the form of a computer system within which a set of instructions may be executed for causing a machine to perform any one or more of the methodologies discussed herein, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The description that follows includes systems, methods, techniques, instruction sequences, and computing machine program products that embody illustrative embodiments of the present disclosure. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of example embodiments. It will be evident, however, to one skilled in the art that the present inventive subject matter may be practiced without these specific details. 
     It will be appreciated that some of the examples disclosed herein are described in the context of virtual machines that are backed up by using base snapshots and incremental snapshots, for example. This should not necessarily be regarded as limiting of the disclosures. The disclosures, systems and methods described herein apply not only to virtual machines of all types that run a file system (for example), but also to network-attached storage (NAS) devices, physical machines (for example, Linux servers), and databases. 
     In existing systems, depending on the size of a given virtual machine, data restoration on the virtual machine may involve a significant amount of data transfer from a backup system to a customer&#39;s environment that hosts the virtual machine. Large amounts of data transfer may cause high workload latency, and latency of virtual machine readiness where the virtual machine is not ready for recovery before the data transfer is completed. 
     Various embodiments described herein relate to an in-place recovery system that provides an in-place data recovery technique that requires, in some examples, only changed data blocks to be identified and transferred to a virtual machine for recovery. This approach can reduce workload latency by reducing virtual machine downtime caused by transferring a large volume of backup data during a recovery process. Example embodiments also improve data integrity of a virtual machine by preserving the virtual machine&#39;s identity, defined in some examples by virtual machine configuration properties. Since the recovery is performed on the same virtual machine (i.e., in-place) at the primary storage platform where it resides, no creation of new virtual machine resulting in the transfer of configuration properties is required. Thereby all properties of the original virtual machine are preserved and remain intact. Further, since the time for recovery in some examples is proportional to the number of data blocks changed, the size of virtual machines does not directly affect the time needed for the recovery. In some examples, the time for recovery is directly or linearly proportional to the number of changed data blocks. By reducing workload latency and efficiently restoring virtual machines, a recovery system that incorporates these techniques can minimize business downtime and allow a steady growth of a customer or user base. 
     In some embodiments of an in-place recovery system, upon receiving a user request to restore a virtual machine to a version at a particular point in time (e.g., first point in time), an in-place recovery system identifies a snapshot (e.g., a first snapshot) associated with the requested version, and generates another snapshot (e.g., a second snapshot) for the virtual machine after taking the virtual machine offline (e.g., when powered off or disconnected from a network). The in-place recovery system compares the first and second snapshots and identifies the original unmodified data blocks (e.g., first data block) in the first snapshot corresponding to the data blocks that were modified (e.g., second data block) in the second snapshot. The in-place recovery system generates reverse incremental backup data that includes the original data blocks in the first snapshot and transfers the reverse incremental backup data to the same virtual machine for restoration. By restoring the virtual machine in-place, the system can leverage the virtual machine&#39;s existing data and configuration properties by only transferring the data affected by the data changes to reverse any changes that occurred subsequent to the requested version for recovery. Further, the system may disregard the snapshots captured beyond the point in time associated with the requested version. By generating a fresh snapshot (e.g., second snapshot) after the virtual machine is taken offline, the system is able to determine the modified data blocks and generate reverse incremental backup data for recovery purposes. 
     In some embodiments, the in-place recovery system identifies a block offset associated with the second data block stored in a disk of the virtual machine. The second data block in the second snapshot includes modified data derived from data content of the first data block in the first snapshot. The system overwrites the second data block with the data content of the first data block based on the identified data offset. In some embodiments, the system identifies a block length associated with the second data block and overwrites the second data block with the data content of the first data block based on the identified block length. 
     In some embodiments, the snapshot (e.g., the first snapshot) identified in the user request is stored in the in-place recovery system&#39;s computing environment instead of the customer&#39;s computing environment where the virtual machine resides. Upon receiving the user request, the in-place recovery system disconnects the virtual machine from a power source or the network in the customer&#39;s computing environment, and generates a fresh snapshot (e.g., the second snapshot) that reflects the current state of the virtual machine. The in-place recovery system reconnects the virtual machine to the virtual power source or the network once the system finishes overwriting the second data block with the reverse incremental backup data. 
     In some embodiment, the in-place recovery system is required to power off the virtual machine in order to overwrite the second data block with the reverse incremental backup data for recovery. 
     In some embodiments, the in-place recovery system deletes the second snapshot from the client environment once the virtual machine is restored in absence of a user request to keep the second snapshot. In some embodiments, the customer&#39;s computing environment is a primary storage platform. The in-place recovery system resides in a host computing environment. The primary storage platform is external to the host computing environment. 
     Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the appended drawings. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. 
       FIG.  1    depicts one embodiment of a networked computing environment  100  in which the disclosed technology may be practiced. As depicted, the networked computing environment  100  includes a data center  104 , a storage appliance  102 , and a computing device  106  in communication with each other via one or more networks  128 . The networked computing environment  100  may also include a plurality of computing devices interconnected through one or more networks  128 . The one or more networks  128  may allow computing devices and/or storage devices to connect to and communicate with other computing devices and/or other storage devices. In some cases, the networked computing environment  100  may include other computing devices and/or other storage devices not shown. The other computing devices may include, for example, a mobile computing device, a non-mobile computing device, a server, a work- station, a laptop computer, a tablet computer, a desktop computer, or an information processing system. The other storage devices may include, for example, a storage area network storage device, a networked-attached storage device, a hard disk drive, a solid-state drive, or a data storage system. 
     The data center  104  may include one or more servers, such as server  200 , in communication with one or more storage devices, such as storage device  108 . The one or more servers may also be in communication with one or more storage appliances, such as storage appliance  102 . The server  200 , storage device  108 , and storage appliance  300  may be in communication with each other via a networking fabric connecting servers and data storage units within the data center  104  to each other. The storage appliance  300  may include a data management system for backing up virtual machines and files within a virtualized infrastructure. In some embodiments, the storage appliance  300  may include an in-place recovery system  334  (as illustrated in  FIG.  3   ) for restoring virtual machines in-place with minimal data blocks being transferred for data recovery. In some embodiments, the in-place recovery system  334  is integrated into the data management system  302 . The server  200  may be used to create and manage one or more virtual machines associated with a virtualized infrastructure. 
     The one or more virtual machines may run various applications, such as a database application or a web server. The storage device  108  may include one or more hardware storage devices for storing data, such as a hard disk drive (HDD), a magnetic tape drive, a solid-state drive (SSD), a storage area network (SAN) storage device, or a Networked-Attached Storage (NAS) device. In some cases, a data center, such as data center  104 , may include thousands of servers and/or data storage devices in communication with each other. The one or more data storage devices  108  may comprise a tiered data storage infrastructure (or a portion of a tiered data storage infrastructure). The tiered data storage infrastructure may allow for the movement of data across different tiers of a data storage infrastructure between higher-cost, higher-performance storage devices (e.g., solid-state drives and hard disk drives) and relatively lower-cost, lower-performance storage devices (e.g., magnetic tape drives). 
     The one or more networks  128  may include a secure network such as an enterprise private network, an unsecure network such as a wireless open network, a local area network (LAN), a wide area network (WAN), and the Internet. The one or more networks  128  may include a cellular network, a mobile network, a wireless network, or a wired network. Each network of the one or more networks  128  may include hubs, bridges, routers, switches, and wired transmission media such as a direct-wired connection. The one or more networks  128  may include an extranet or other private network for securely sharing information or providing controlled access to applications or files. 
     A server, such as server  200 , may allow a client to download information or files (e.g., executable, text, application, audio, image, or video files) from the server  200  or to perform a search query related to particular information stored on the server  200 . In some cases, a server may act as an application server or a file server. In general, server  200  may refer to a hardware device that acts as the host in a client-server relationship or a software process that shares a resource with or performs work for one or more clients. 
     One embodiment of server  200  includes a network interface  110 , processor  112 , memory  114 , disk  116 , and virtualization manager  118  all in communication with each other. Network interface  110  allows server  200  to connect to one or more networks  128 . Network interface  110  may include a wireless network interface and/or a wired network interface. Processor  112  allows server  200  to execute computer-readable instructions stored in memory  114  in order to perform processes described herein. Processor  112  may include one or more processing units, such as one or more CPUs and/or one or more GPUs. Memory  114  may comprise one or more types of memory (e.g., RAM, SRAM, DRAM, ROM, EEPROM, Flash, etc.). Disk  116  may include a hard disk drive and/or a solid-state drive. Memory  114  and disk  116  may comprise hardware storage devices. 
     The virtualization manager  118  may manage a virtualized infrastructure and perform management operations associated with the virtualized infrastructure. The virtualization manager  118  may manage the provisioning of virtual machines running within the virtualized infrastructure and provide an interface to computing devices interacting with the virtualized infrastructure. In one example, the virtualization manager  118  may set a virtual machine having a virtual disk into a frozen state in response to a snapshot request made via an application programming interface (API) by a storage appliance, such as storage appliance  300 . Setting the virtual machine into a frozen state may allow a point in time snapshot of the virtual machine to be stored or transferred. In one example, updates made to a virtual machine that has been set into a frozen state may be written to a separate file (e.g., an update file) while the virtual disk may be set into a read-only state to prevent modifications to the virtual disk file while the virtual machine is in the frozen state. 
     The virtualization manager  118  may then transfer backup data associated with the virtual machine to a storage appliance (e.g., a storage appliance  102  or storage appliance  300  of  FIG.  1   , described further below) in response to a request made by a user via the storage appliance. For example, the backup data may include an image of the virtual machine (e.g., base snapshot) or a portion of the image of the virtual disk file (e.g., incremental snapshot) associated with the state of the virtual disk at the point in time when it is frozen. 
     In some embodiments, after the data associated with the point in time snapshot of the virtual machine has been transferred to the storage appliance  300 , the virtual machine may be released from the frozen state (i.e., unfrozen) and the updates made to the virtual machine and stored in the separate file may be merged into the virtual disk file. The virtualization manager  118  may perform various virtual machine-related tasks, such as cloning virtual machines, creating new virtual machines, monitoring the state of virtual machines, moving virtual machines between physical hosts for load balancing purposes, and facilitating backups of virtual machines. 
     In some embodiments, the storage appliance  300  and storage appliance  102  each includes a network interface  120 , processor  122 , memory  124 , and disk  126  all in communication with each other. Network interface  120  allows storage appliance  300  to connect to one or more networks  128 . Network interface  120  may include a wireless network interface and/or a wired network interface. Processor  122  allows storage appliance  300  to execute computer-readable instructions stored in memory  124  in order to perform processes described herein. Processor  122  may include one or more processing units, such as one or more CPUs and/or one or more GPUs. Memory  124  may comprise one or more types of memory (e.g., RAM, SRAM, DRAM, ROM, EEPROM, NOR Flash, NAND Flash, etc.). Disk  126  may include a hard disk drive and/or a solid-state drive. Memory  124  and disk  126  may comprise hardware storage devices. 
     In some embodiments, the storage appliance  300  may include four machines. Each of the four machines may include a multi-core CPU, 64 GB of RAM, a 400 GB SSD, three 4 TB HDDs, and a network interface controller. In this case, the four machines may be in communication with one or more networks  128  via the four network interface controllers. The four machines may comprise four nodes of a server cluster. The server cluster may comprise a set of physical machines that are connected together via a network. The server cluster may be used for storing data associated with a plurality of virtual machines, such as backup data associated with different point-in-time versions of the virtual machines. 
     The networked computing environment  100  may provide a cloud computing environment for one or more computing devices. Cloud computing may refer to Internet-based computing, wherein shared resources, software, and/or information may be provided to one or more computing devices on-demand via the Internet. The networked computing environment  100  may comprise a cloud computing environment providing Software-as-a-Service (SaaS) or Infrastructure- as-a-Service (IaaS) services. SaaS may refer to a software distribution model in which applications are hosted by a service provider and made available to end-users over the Internet. In some embodiments, the networked computing environment  100  may include a virtualized infrastructure that provides software, data processing, and/or data storage services to end-users accessing the services via the networked computing environment  100 . In one example, networked computing environment  100  may provide cloud-based work productivity or business-related applications to a computing device, such as computing device  106 . The storage appliance  102  may comprise a cloud-based data management system for backing up virtual machines and/or files within a virtualized infrastructure, such as virtual machines running on server  200 /or files stored on server  200 . 
     In some cases, networked computing environment  100  may provide remote access to secure applications and files stored within data center  104  from a remote computing device, such as computing device  106 . The data center  104  may use an access control application to manage remote access to protected resources, such as protected applications, databases, or files located within the data center  104 . To facilitate remote access to secure applications and files, a secure network connection may be established using a virtual private network (VPN). A VPN connection may allow a remote computing device, such as computing device  106 , to securely access data from a private network (e.g., from a company file server or mail server) using an unsecure public network or the Internet. The VPN connection may require client-side software (e.g., running on the remote computing device) to establish and maintain the VPN connection. The VPN client software may provide data encryption and encapsulation prior to the transmission of secure private network traffic through the Internet. 
     In some embodiments, the storage appliance  300  may manage the extraction and storage of virtual machine snapshots associated with different point in time versions of one or more virtual machines running within the data center  104 . A snapshot of a virtual machine may correspond with a state of the virtual machine at a particular point-in-time. In response to a restore command from the storage device  108 , the storage appliance  300  may restore a point-in-time version of a virtual machine (e.g., base snapshot) or restore point-in-time versions of one or more files located on the virtual machine (e.g., incremental snapshot) and transmit the restored data to the server  200 . In response to a mount command from the server  200 , the storage appliance  300  may allow a point-in-time version of a virtual machine to be mounted and allow the server  200  to read and/or modify data associated with the point-in-time version of the virtual machine. To improve storage density, the storage appliance  300  may deduplicate and compress data associated with different versions of a virtual machine and/or deduplicate and compress data associated with different virtual machines. To improve system performance, the storage appliance  300  may first store virtual machine snapshots received from a virtualized environment in a cache, such as a flash-based cache. The cache may also store popular data or frequently accessed data (e.g., based on a history of virtual machine restorations, incremental files associated with commonly restored virtual machine versions) and current day incremental files or incremental files corresponding with snapshots captured within the past 24 hours. 
     An incremental file may comprise a forward incremental file or a reverse incremental file. A forward incremental file may include a set of data representing changes that have occurred since an earlier point-in-time snapshot of a virtual machine. To generate a snapshot of the virtual machine corresponding with a forward incremental file, the forward incremental file may be combined with an earlier point in time snapshot of the virtual machine (e.g., the forward incremental file may be combined with the last full image of the virtual machine that was captured before the forward incremental file was captured and any other forward incremental files that were captured subsequent to the last full image and prior to the forward incremental file). A reverse incremental file may include a set of data representing changes from a later point-in-time snapshot of a virtual machine. To generate a snapshot of the virtual machine corresponding with a reverse incremental file, the reverse incremental file may be combined with a later point-in-time snapshot of the virtual machine (e.g., the reverse incremental file may be combined with the most recent snapshot of the virtual machine and any other reverse incremental files that were captured prior to the most recent snapshot and subsequent to the reverse incremental file). 
     The storage appliance  300  may provide a user interface (e.g., a web-based interface or a graphical user interface) that displays virtual machine backup information such as identifications of the protected virtual machines and the historical versions or time machine views for each of the protected virtual machines protected. A time machine view of a virtual machine may include snapshots of the virtual machine over a plurality of points in time. Each snapshot may comprise the state of the virtual machine at a particular point in time. Each snapshot may correspond with a different version of the virtual machine (e.g., Version 1 of a virtual machine may correspond with the state of the virtual machine at a first point in time and Version 2 of the virtual machine may correspond with the state of the virtual machine at a second point in time subsequent to the first point in time). 
     In one example, The user interface may enable an end-user of the storage appliance  300  (e.g., a system administrator or a virtualization administrator) to select a particular version of a virtual machine to be mounted. When a particular version of a virtual machine has been mounted, the particular version may be accessed by a client (e.g., a virtual machine, a physical machine, or a computing device) as if the particular version was local to the client. A mounted version of a virtual machine may correspond with a mount point directory (e.g., /snapshots/VM5Nersion23). In one example, the storage appliance  300  may run an NFS server and make the particular version (or a copy of the particular version) of the virtual machine accessible for reading and writing. The end-user of the storage appliance  300  may then select the particular version to be mounted and run an application (e.g., a data analytics application) using the mounted version of the virtual machine. In another example, the particular version may be mounted as an Internet Small Computer System Interface (iSCSI) target. 
     In some embodiments, the user interface may enable an end-user of the storage appliance  300  (e.g., a system administrator or a virtualization administrator) to select a particular version of a virtual machine to be restored. For example, a user may send, via the user interface, a request to restore a virtual machine to a version corresponding to a particular point in time (e.g., the first point in time). 
       FIG.  2    depicts one embodiment of server  200  of  FIG.  1   . The server  200  may comprise one server out of a plurality of servers that are networked together within a data center (e.g., data center  104 ). In one example, the plurality of servers may be positioned within one or more server racks within the data center. As depicted, the server  200  includes hardware-level components and software-level components. The hardware-level components include one or more processors  202 , one or more memory  204 , and one or more disks  206 . The software-level components include a hypervisor  208 , a virtualized infrastructure manager  222 , and one or more virtual machines, such as virtual machine  220 . The hypervisor  208  may comprise a native hypervisor or a hosted hypervisor. The hypervisor  208  may provide a virtual operating platform for running one or more virtual machines, such as virtual machine  220 . Virtual machine  220  includes a plurality of virtual hardware devices including a virtual processor  210 , a virtual memory  212 , and a virtual disk  214 . The virtual disk  214  may comprise a file stored within the one or more disks  206 . In one example, a virtual machine  220  may include a plurality of virtual disks  214 , with each virtual disk of the plurality of virtual disks  214  associated with a different file stored on the one or more disks  206 . Virtual machine  220  may include a guest operating system  216  that runs one or more applications, such as application  218 . 
     The virtualized infrastructure manager  222 , which may correspond with the virtualization manager  118  in  FIG.  1   , may run on a virtual machine or natively on the server  200 . The virtual machine may, for example, be or include the virtual machine  220  or a virtual machine separate from the server  200 . Other arrangements are possible. The virtualized infrastructure manager  222  may provide a centralized platform for managing a virtualized infrastructure that includes a plurality of virtual machines. The virtualized infrastructure manager  222  may manage the provisioning of virtual machines running within the virtualized infrastructure and provide an interface to computing devices interacting with the virtualized infrastructure. The virtualized infrastructure manager  222  may perform various virtualized infrastructure related tasks, such as cloning virtual machines, creating new virtual machines, monitoring the state of virtual machines, and facilitating backups of virtual machines. 
     In some embodiments, the server  200  may use the virtualized infrastructure manager  222  to facilitate backups for a plurality of virtual machines (e.g., eight different virtual machines) running on the server  200 . Each virtual machine running on the server  200  may run its own guest operating system and its own set of applications. Each virtual machine running on the server  200  may store its own set of files using one or more virtual disks associated with the virtual machine (e.g., each virtual machine may include two virtual disks that are used for storing data associated with the virtual machine). 
     In some embodiments, a data management application running on a storage appliance, such as storage appliance  102  in  FIG.  1    or storage appliance  300  in  FIG.  1   , may request a snapshot of a virtual machine running on server  200 . The snapshot of the virtual machine may be stored as one or more files, with each file associated with a virtual disk of the virtual machine. A snapshot of a virtual machine may correspond with a state of the virtual machine at a particular point in time. The particular point in time may be associated with a time stamp. In one example, a first snapshot of a virtual machine may correspond with a first state of the virtual machine (including the state of applications and files stored on the virtual machine) at a first point in time and a second snapshot of the virtual machine may correspond with a second state of the virtual machine at a second point in time subsequent to the first point in time. 
     In some embodiments, in response to a request for a snapshot of a virtual machine at a particular point in time, the virtualized infrastructure manager  222  may set the virtual machine into a frozen state or store a copy of the virtual machine at the particular point in time. The virtualized infrastructure manager  222  may then transfer data associated with the virtual machine (e.g., an image of the virtual machine or a portion of the image of the virtual machine) to the storage appliance  300  or storage appliance  102 . The data (e.g., backup data) associated with the virtual machine may include a set of files including a virtual disk file storing contents of a virtual disk of the virtual machine at the particular point in time and a virtual machine configuration file (e.g., database schema and database control logic data items) storing configuration settings for the virtual machine at the particular point in time. The contents of the virtual disk file may include the operating system used by the virtual machine, local applications stored on the virtual disk, and user files (e.g., images and word processing documents). In some cases, the virtualized infrastructure manager  222  may transfer a full image of the virtual machine to the storage appliance  102  or storage appliance  300  of  FIG.  1    or a plurality of data blocks corresponding with the full image (e.g., to enable a full image-level backup of the virtual machine to be stored on the storage appliance). In other cases, the virtualized infrastructure manager  222  may transfer a portion of an image of the virtual machine associated with data that has changed since an earlier point in time prior to the particular point in time or since a last snapshot of the virtual machine was taken. In one example, the virtualized infrastructure manager  222  may transfer only data associated with virtual blocks stored on a virtual disk of the virtual machine that have changed since the last snapshot of the virtual machine was taken. In some embodiments, the data management application may specify a first point in time and a second point in time and the virtualized infrastructure manager  222  may output one or more virtual data blocks associated with the virtual machine that have been modified between the first point in time and the second point in time. 
     In some embodiments, the server  200  or the hypervisor  208  may communicate with a storage appliance, such as storage appliance  102  in  FIG.  1    or storage appliance  300  in  FIG.  1   , using a distributed file system protocol such as Network File System (NFS) Version 3, or Server Message Block (SMB) protocol. The distributed file system protocol may allow the server  200  or the hypervisor  208  to access, read, write, or modify files stored on the storage appliance as if the files were locally stored on the server  200 . The distributed file system protocol (e.g., Network File System (“NFS”) protocol) may allow the server  200  or the hypervisor  208  to mount a directory or a portion of a file system located within the storage appliance. 
       FIG.  3    depicts one embodiment of storage appliance  300  in  FIG.  1   . The storage appliance may include a plurality of physical machines and virtual machines that may act in concert as a single computing system. Each physical machine of the plurality of physical machines may comprise a node in a cluster. In one example, the storage appliance may be positioned within a server rack within a data center. As depicted, the storage appliance  300  includes hardware-level components and software-level components. The hardware-level components include one or more physical machines, such as physical machine  314  and physical machine  324 . The physical machine  314  includes a network interface  316 , processor  318 , memory  320 , and disk  322  all in communication with each other. Processor  318  allows physical machine  314  to execute computer readable instructions stored in memory  320  to perform processes described herein. Disk  322  may include a hard disk drive and/or a solid-state drive. The physical machine  324  includes a network interface  326 , processor  328 , memory  330 , and disk  332  all in communication with each other. Processor  328  allows physical machine  324  to execute computer readable instructions stored in memory  330  to perform processes described herein. Disk  332  may include a hard disk drive and/or a solid-state drive. In some cases, disk  332  may include a flash-based SSD or a hybrid HDD/SSD drive. In some embodiments, the storage appliance  300  may include a plurality of physical machines arranged in a cluster (e.g., eight machines in a cluster). Each of the plurality of physical machines may include a plurality of multi-core CPUs, 108 GB of RAM, a 500 GB SSD, four 4 TB HDDs, and a network interface controller. 
     In some embodiments, the plurality of physical machines may be used to implement a cluster-based network fileserver. The cluster-based network file server may neither require nor use a front-end load balancer. One issue with using a front-end load balancer to host the IP address for the cluster-based network file server and to forward requests to the nodes of the cluster-based network file server is that the front-end load balancer comprises a single point of failure for the cluster-based network file server. In some cases, the file system protocol used by a server, such as server  200  in  FIG.  1   , or a hypervisor, such as hypervisor  208  in  FIG.  2   , to communicate with the storage appliance  300  may not provide a failover mechanism (e.g., NFS Version 3). In the case that no failover mechanism is provided on the client side, the hypervisor may not be able to connect to a new node within a cluster in the event that the node connected to the hypervisor fails. 
     In some embodiments, each node in a cluster may be connected to each other via a network and may be associated with one or more IP addresses (e.g., two different IP addresses may be assigned to each node). In one example, each node in the cluster may be assigned a permanent IP address and a floating IP address and may be accessed using either the permanent IP address or the floating IP address. In this case, a hypervisor, such as hypervisor  208  in  FIG.  2   , may be configured with a first floating IP address associated with a first node in the cluster. The hypervisor may connect to the cluster using the first floating IP address. In one example, the hypervisor may communicate with the cluster using the NFS Version 3 protocol. Each node in the cluster may run a Virtual Router Redundancy Protocol (VRRP) daemon. A daemon may comprise a background process. Each VRRP daemon may include a list of all floating IP addresses available within the cluster. In the event that the first node associated with the first floating IP address fails, one of the VRRP daemons may automatically assume or pick up the first floating IP address if no other VRRP daemon has already assumed the first floating IP address. Therefore, if the first node in the cluster fails or otherwise goes down, then one of the remaining VRRP daemons running on the other nodes in the cluster may assume the first floating IP address that is used by the hypervisor for communicating with the cluster. 
     In order to determine which of the other nodes in the cluster will assume the first floating IP address, a VRRP priority may be established. In one example, given a number (N) of nodes in a cluster from node(0) to node(N-1), for a floating IP address (i), the VRRP priority of nodeG) may be G-i) modulo N. In another example, given a number (N) of nodes in a cluster from node(0) to node(N-1), for a floating IP address (i), the VRRP priority of nodeG) may be (i-j) modulo N. In these cases, nodeG) will assume floating IP address (i) only if its VRRP priority is higher than that of any other node in the cluster that is alive and announcing itself on the network. Thus, if a node fails, then there may be a clear priority ordering for determining which other node in the cluster will take over the failed node&#39;s floating IP address. 
     In some cases, a cluster may include a plurality of nodes and each node of the plurality of nodes may be assigned a different floating IP address. In this case, a first hypervisor may be configured with a first floating IP address associated with a first node in the cluster, a second hypervisor may be configured with a second floating IP address associated with a second node in the cluster, and a third hypervisor may be configured with a third floating IP address associated with a third node in the cluster. 
     As depicted in  FIG.  3   , the software-level components of the storage appliance  300  may include data management system  302 , in-place recovery system  334 , a virtualization interface  304 , a distributed job scheduler  308 , a distributed metadata store  310 , a distributed file system  312 , and one or more virtual machine search indexes, such as virtual machine search index  306 . In some embodiments, the in-place recovery system  334  may be a software-level component of a storage appliance  300  in a networked computing environment  100 . In some embodiments, the in-place recovery system may be integrated into a data management system for restoring virtual machines in-place with only changed data blocks being transferred for data recovery, as explained further in  FIGS.  3 , and  5 - 7   . 
     In some embodiments, the software-level components of the storage appliance  300  may be run using a dedicated hardware-based appliance. In another embodiment, the software-level components of the storage appliance  300  may be run from the cloud (e.g., the software-level components may be installed on a cloud service provider). 
     In some cases, the data storage across a plurality of nodes in a cluster (e.g., the data storage available from the one or more physical machine (e.g., physical machine  314  and physical machine  324 )) may be aggregated and made available over a single file system namespace (e.g., /snapshots/). A directory for each virtual machine protected using the storage appliance  300  may be created (e.g., the directory for Virtual Machine A may be /snapshots/VM_A). Snapshots and other data associated with a virtual machine may reside within the directory for the virtual machine. In one example, snapshots of a virtual machine may be stored in subdirectories of the directory (e.g., a first snapshot of Virtual Machine A may reside in /snapshots/VM_A/s1/ and a second snapshot of Virtual Machine A may reside in /snapshots/VM_A/s2/). 
     The distributed file system  312  may present itself as a single file system, in which as new physical machines or nodes are added to the storage appliance  300 , the cluster may automatically discover the additional nodes and automatically increase the available capacity of the file system for storing files and other data. Each file stored in the distributed file system  312  may be partitioned into one or more chunks or shards. Each of the one or more chunks may be stored within the distributed file system  312  as a separate file. The files stored within the distributed file system  312  may be replicated or mirrored over a plurality of physical machines, thereby creating a load-balanced and fault tolerant distributed file system. In one example, storage appliance  300  may include ten physical machines arranged as a failover cluster and a first file corresponding with a snapshot of a virtual machine (e.g., /snapshots/VM_A/s1/s1.full) may be replicated and stored on three of the ten machines. 
     The distributed metadata store  310  may include a distributed database management system that provides high availability without a single point of failure. In some embodiments, the distributed metadata store  310  may comprise a database, such as a distributed document-oriented database. The distributed metadata store  310  may be used as a distributed key value storage system. In one example, the distributed metadata store  310  may comprise a distributed NoSQL key value store database. In some cases, the distributed metadata store  310  may include a partitioned row store, in which rows are organized into tables or other collections of related data held within a structured format within the key value store database. A table (or a set of tables) may be used to store metadata information associated with one or more files stored within the distributed file system  312 . The metadata information may include the name of a file, a size of the file, file permissions associated with the file, when the file was last modified, and file mapping information associated with an identification of the location of the file stored within a cluster of physical machines. In some embodiments, a new file corresponding with a snapshot of a virtual machine may be stored within the distributed file system  312  and metadata associated with the new file may be stored within the distributed metadata store  310 . The distributed metadata store  310  may also be used to store a backup schedule for the virtual machine and a list of snapshots for the virtual machine that are stored using the storage appliance  300 . 
     In some cases, the distributed metadata store  310  may be used to manage one or more versions of a virtual machine. Each version of the virtual machine may correspond with a full image snapshot of the virtual machine stored within the distributed file system  312  or an incremental snapshot of the virtual machine (e.g., a forward incremental or reverse incremental) stored within the distributed file system  312 . In some embodiments, the one or more versions of the virtual machine may correspond with a plurality of files. The plurality of files may include a single full image snapshot of the virtual machine and one or more incremental aspects derived from the single full image snapshot. The single full image snapshot of the virtual machine may be stored using a first storage device of a first type (e.g., a HDD) and the one or more incremental aspects derived from the single full image snapshot may be stored using a second storage device of a second type (e.g., an SSD). In this case, only a single full image needs to be stored and each version of the virtual machine may be generated from the single full image or the single full image combined with a subset of the one or more incremental aspects. Furthermore, each version of the virtual machine may be generated by performing a sequential read from the first storage device (e.g., reading a single file from a HDD) to acquire the full image and, in parallel, performing one or more reads from the second storage device (e.g., performing fast random reads from an SSD) to acquire the one or more incremental aspects. 
     The distributed job scheduler  308  may be used for scheduling backup jobs that acquire and store virtual machine snapshots for one or more virtual machines over time. The distributed job scheduler  308  may follow a backup schedule to back up an entire image of a virtual machine at a particular point in time or one or more virtual disks associated with the virtual machine at the particular point in time. In one example, the backup schedule may specify that the virtual machine be backed up at a snapshot capture frequency, such as every two hours or every 24 hours. Each backup job may be associated with one or more tasks to be performed in a sequence. Each of the one or more tasks associated with a job may be run on a particular node within a cluster. In some cases, the distributed job scheduler  308  may schedule a specific job to be run on a particular node based on data stored on the particular node. For example, the distributed job scheduler  308  may schedule a virtual machine snapshot job to be run on a node in a cluster that is used to store snapshots of the virtual machine in order to reduce network congestion. 
     The distributed job scheduler  308  may comprise a distributed fault tolerant job scheduler, in which jobs affected by node failures are recovered and rescheduled to be run on available nodes. In some embodiments, the distributed job scheduler  308  may be fully decentralized and implemented without the existence of a master node. The distributed job scheduler  308  may run job scheduling processes on each node in a cluster or on a plurality of nodes in the cluster. In one example, the distributed job scheduler  308  may run a first set of job scheduling processes on a first node in the cluster, a second set of job scheduling processes on a second node in the cluster, and a third set of job scheduling processes on a third node in the cluster. The first set of job scheduling processes, the second set of job scheduling processes, and the third set of job scheduling processes may store information regarding jobs, schedules, and the states of jobs using a metadata store, such as distributed metadata store  310 . In the event that the first node running the first set of job scheduling processes fails (e.g., due to a network failure or a physical machine failure), the states of the jobs managed by the first set of job scheduling processes may fail to be updated within a threshold period of time (e.g., a job may fail to be completed within 30 seconds or within minutes from being started). In response to detecting jobs that have failed to be updated within the threshold period of time, the distributed job scheduler  308  may undo and restart the failed jobs on available nodes within the cluster. 
     The job scheduling processes running on at least a plurality of nodes in a cluster (e.g., on each available node in the cluster) may manage the scheduling and execution of a plurality of jobs. The job scheduling processes may include run processes for running jobs, cleanup processes for cleaning up failed tasks, and rollback processes for rolling-back or undoing any actions or tasks performed by failed jobs. In some embodiments, the job scheduling processes may detect that a particular task for a particular job has failed and in response may perform a cleanup process to clean up or remove the effects of the particular task and then perform a rollback process that processes one or more completed tasks for the particular job in reverse order to undo the effects of the one or more completed tasks. Once the particular job with the failed task has been undone, the job scheduling processes may restart the particular job on an available node in the cluster. 
     The distributed job scheduler  308  may manage a job in which a series of tasks associated with the job are to be performed atomically (i.e., partial execution of the series of tasks is not permitted). If the series of tasks cannot be completely executed or there is any failure that occurs to one of the series of tasks during execution (e.g., a hard disk associated with a physical machine fails or a network connection to the physical machine fails), then the state of a data management system may be returned to a state as if none of the series of tasks was ever performed. The series of tasks may correspond with an ordering of tasks for the series of tasks and the distributed job scheduler  308  may ensure that each task of the series of tasks is executed based on the ordering of tasks. Tasks that do not have dependencies with each other may be executed in parallel. 
     In some cases, the distributed job scheduler  308  may schedule each task of a series of tasks to be performed on a specific node in a cluster. In other cases, the distributed job scheduler  308  may schedule a first task of the series of tasks to be performed on a first node in a cluster and a second task of the series of tasks to be performed on a second node in the cluster. In these cases, the first task may have to operate on a first set of data (e.g., a first file stored in a file system) stored on the first node and the second task may have to operate on a second set of data (e.g., metadata related to the first file that is stored in a database) stored on the second node. In some embodiments, one or more tasks associated with a job may have an affinity to a specific node in a cluster. 
     In one example, if the one or more tasks require access to a database that has been replicated on three nodes in a cluster, then the one or more tasks may be executed on one of the three nodes. In another example, if the one or more tasks require access to multiple chunks of data associated with a virtual disk that has been replicated over four nodes in a cluster, then the one or more tasks may be executed on one of the four nodes. Thus, the distributed job scheduler  308  may assign one or more tasks associated with a job to be executed on a particular node in a cluster based on the location of data to be accessed by the one or more tasks. 
     In some embodiments, the distributed job scheduler  308  may manage a first job associated with capturing and storing a snapshot of a virtual machine periodically (e.g., every 30 minutes). The first job may include one or more tasks, such as communicating with a virtualized infrastructure manager, such as the virtualized infrastructure manager  222  in  FIG.  2   , to create a frozen copy of the virtual machine and to transfer one or more chunks (or one or more files) associated with the frozen copy to a storage appliance, such as storage appliance  300  in  FIG.  1   . The one or more tasks may also include generating metadata for the one or more chunks, storing the metadata using the distributed metadata store  310 , storing the one or more chunks within the distributed file system  312 , and communicating with the virtualized infrastructure manager  222  that the frozen copy of the virtual machine may be unfrozen or released from a frozen state. The metadata for a first chunk of the one or more chunks may include information specifying a version of the virtual machine associated with the frozen copy, a time associated with the version (e.g., the snapshot of the virtual machine was taken at 5:30 p.m. on Jun. 29, 2018), and a file path to where the first chunk is stored within the distributed file system  312  (e.g., the first chunk is located at /snapshotsNM_B/s1/s1.chunk1). The one or more tasks may also include deduplication, compression (e.g., using a lossless data compression algorithm such as LZ4 or LZ77), decompression, encryption (e.g., using a symmetric key algorithm such as Triple DES or AES-256), and decryption related tasks. 
     The virtualization interface  304  may provide an interface for communicating with a virtualized infrastructure manager managing a virtualization infrastructure, such as virtualized infrastructure manager  222  in  FIG.  2   , and requesting data associated with virtual machine snapshots from the virtualization infrastructure. The virtualization interface  304  may communicate with the virtualized infrastructure manager using an Application Programming Interface (API) for accessing the virtualized infrastructure manager (e.g., to communicate a request for a snapshot of a virtual machine). In this case, storage appliance  300  may request and receive data from a virtualized infrastructure without requiring agent software to be installed or running on virtual machines within the virtualized infrastructure. The virtualization interface  304  may request data associated with virtual blocks stored on a virtual disk of the virtual machine that have changed since a last snapshot of the virtual machine was taken or since a specified prior point in time. Therefore, in some cases, if a snapshot of a virtual machine is the first snapshot taken of the virtual machine, then a full image of the virtual machine may be transferred to the storage appliance. However, if the snapshot of the virtual machine is not the first snapshot taken of the virtual machine, then only the data blocks of the virtual machine that have changed since a prior snapshot was taken may be transferred to the storage appliance. 
     The virtual machine search index  306  may include a list of files that have been stored using a virtual machine and a version history for each of the files in the list. Each version of a file may be mapped to the earliest point-in-time snapshot of the virtual machine that includes the version of the file or to a snapshot of the virtual machine that includes the version of the file (e.g., the latest point in time snapshot of the virtual machine that includes the version of the file). In some embodiments, the virtual machine search index  306  may be used to identify a version of the virtual machine that includes a particular version of a file (e.g., a particular version of a database, a spreadsheet, or a word processing document). In some cases, each of the virtual machines that are backed up or protected using storage appliance  300  may have a corresponding virtual machine search index. 
     In some embodiments, as each snapshot of a virtual machine is ingested, each virtual disk associated with the virtual machine is parsed in order to identify a file system type associated with the virtual disk and to extract metadata (e.g., file system metadata) for each file stored on the virtual disk. The metadata may include information for locating and retrieving each file from the virtual disk. The metadata may also include a name of a file, the size of the file, the last time at which the file was modified, and a content checksum for the file. Each file that has been added, deleted, or modified since a previous snapshot was captured may be determined using the metadata (e.g., by comparing the time at which a file was last modified with a time associated with the previous snapshot). Thus, for every file that has existed within any of the snapshots of the virtual machine, a virtual machine search index may be used to identify when the file was first created (e.g., corresponding with a first version of the file) and at what times the file was modified (e.g., corresponding with subsequent versions of the file). Each version of the file may be mapped to a particular version of the virtual machine that stores that version of the file. 
     In some cases, if a virtual machine includes a plurality of virtual disks, then a virtual machine search index may be generated for each virtual disk of the plurality of virtual disks. For example, a first virtual machine search index may catalog and map files located on a first virtual disk of the plurality of virtual disks and a second virtual machine search index may catalog and map files located on a second virtual disk of the plurality of virtual disks. In this case, a global file catalog or a global virtual machine search index for the virtual machine may include the first virtual machine search index and the second virtual machine search index. A global file catalog may be stored for each virtual machine backed up by a storage appliance within a file system, such as distributed file system  312  in  FIG.  3   . 
     The data management system  302  may comprise an application running on the storage appliance  300  that manages and stores one or more snapshots of a virtual machine. In one example, the data management system  302  may comprise a highest-level layer in an integrated software stack running on the storage appliance. The integrated software stack may include the data management system  302 , the virtualization interface  304 , the distributed job scheduler  308 , the distributed metadata store  310 , and the distributed file system  312 . 
     In some cases, the integrated software stack may run on other computing devices, such as a server or computing device  106  in  FIG.  1   . The data management system  302  may use the virtualization interface  304 , the distributed job scheduler  308 , the distributed metadata store  310 , and the distributed file system  312  to manage and store one or more snapshots of a virtual machine. Each snapshot of the virtual machine may correspond with a point-in-time version of the virtual machine. The data management system  302  may generate and manage a list of versions for the virtual machine. Each version of the virtual machine may map to or reference one or more chunks or one or more files stored within the distributed file system  312 . Combined together, the one or more chunks and/or the one or more files stored within the distributed file system  312  may comprise a full image of the version of the virtual machine. 
       FIG.  4    shows an example cluster  400  of a distributed decentralized database, according to some embodiments. As illustrated, the example cluster  400  includes five nodes, nodes 1-5. In some embodiments, each of the five nodes runs from different machines, such as physical machine  314  in  FIG.  3    or virtual machine  220  in  FIG.  2   . The nodes in the example cluster  400  can include instances of peer nodes of a distributed database (e.g., cluster-based database, distributed decentralized database management system, a NoSQL database, Apache Cassandra, DataStax, MongoDB, CouchDB), according to some embodiments. The distributed database system is distributed in that data is sharded or distributed across the example cluster  400  in shards or chunks and decentralized in that there is no central storage device and no single point of failure. The system operates under the assumption that multiple nodes may go down, up, or become non-responsive. 
     In some embodiments, data written to one of the nodes is replicated to one or more other nodes per a replication protocol of the example cluster  400 . For example, data written to node 1 can be replicated to nodes 2 and 3. If node 1 prematurely terminates, node 2 and/or 3 can be used to provide the replicated data. In some embodiments, each node of example cluster  400  frequently exchanges state information about itself and other nodes across the example cluster  400  using gossip protocol. Gossip protocol is a peer-to-peer communication protocol in which each node randomly shares (e.g., communicates, requests, transmits) location and state information about the other nodes in a given cluster. 
     Writing: For a given node, a sequentially written commit log captures the write activity to ensure data durability. The data is then written to an in-memory structure (e.g., a memtable, write-back cache). Each time the in-memory structure is full, the data is written to disk in a Sorted String Table data file. In some embodiments, writes are automatically partitioned and replicated throughout the example cluster  400 . 
     Reading: Any node of example cluster  400  can receive a read request (e.g., query) from an external client. If the node that receives the read request manages the data requested, the node provides the requested data. If the node does not manage the data, the node determines which node manages the requested data. The node that received the read request then acts as a proxy between the requesting entity and the node that manages the data (e.g., the node that manages the data sends the data to the proxy node, which then provides the data to an external entity that generated the request). 
     The distributed decentralized database system is decentralized in that there is no single point of failure due to the nodes being symmetrical and seamlessly replaceable. For example, whereas conventional distributed data implementations have nodes with different functions (e.g., master/slave nodes, asymmetrical database nodes, federated databases), the nodes of example cluster  400  are configured to function the same way (e.g., as symmetrical peer database nodes that communicate via gossip protocol, such as Cassandra nodes) with no single point of failure. If one of the nodes in example cluster  400  terminates prematurely (“goes down”), another node can rapidly take the place of the terminated node without disrupting service. The example cluster  400  can be a container for a keyspace, which is a container for data in the distributed decentralized database system (e.g., whereas a database is a container for containers in conventional relational databases, the Cassandra keyspace is a container for a Cassandra database system). 
       FIG.  5    depicts a flowchart of process  500  indicating example in-place virtual machine recovery operations in a method, according to some embodiments. The operations of process  500  may be performed by any number of different systems, such as the in-place recovery system  334  or the data management system  302  as described herein, or any portion thereof, such as a processor included in any of the systems. 
     The operations of process  500  starts with operation  502 . At operation  502 , the in-place recovery system  334  receives a user request via a user interface (e.g., a web-based interface or a graphical user interface) that displays virtual machine backup information such as identifications of the protected virtual machines and the historical versions or time machine views for each of the protected virtual machines protected. The user request instructs in-place recovery system  334  to restore a particular virtual machine in a primary storage platform to a version corresponding to a first point in time. The virtual machine is associated with a plurality of configuration properties, at least including a number of CPUs, the size of memory, and a number of disks associated with the particular virtual machine. In some examples, the virtual machine configuration is the arrangement of resources assigned to a virtual machine. The resources allocated to a virtual machine may include the allocated properties, such as processors, memory, disks, network adapters, user interface, etc. 
     At operation  504 , the in-place recovery system  334  identifies a first snapshot of the virtual machine based on the user request. The identification may be based on a sequence number assigned to the first snapshot in the request. In some examples, the sequence number refers to the first snapshot being captured at the first point in time. 
     At operation  506 , the in-place recovery system  334  generates a second snapshot of the virtual machine at the second point in time. The second point time is subsequent to the first point in time. At operation  508 , the in-place recovery system  334  identifies a second data block in the second snapshot that includes modified data derived from, or based on, the data content of a first data block in the first snapshot. For example, system  334  may track or use a third-party data block tracking service to track all blocks changed between the first snapshot and the second snapshot. In some examples, each snapshot is identified by a sequence number, as a unique identifier. The sequence number of each snapshot is saved along with other metadata of the snapshot. In some embodiments, the third-party data block tracking service may be VMWARE Changed Block Tracking (CBT). 
     In some embodiments, the virtual machine resides in the primary storage platform external to the in-place recovery system  334 . The first snapshot was generated for the virtual machine and transferred to the in-place recovery system  334  for backup storage. In embodiments, the first snapshot is removed from the primary storage platform after being transferred to the in-place recovery system  334  to save storage space. 
     In some embodiments, the block changes are identified at the primary storage platform using the third-party data block tracking service associated with the primary storage platform. For example, the third-party data block tracking service tracks all blocks changed before the first snapshot and the second snapshot. When the second snapshot is taken, the third-party data block tracking service may provide system  334  a record of all the blocks changed from the first snapshot corresponding to the first point in time and the second snapshot corresponding to the second point in time. Based on the record provided, system  334  may determine data blocks (e.g., including the first data block) in the first snapshot that corresponds to the data changes in the modified data blocks (e.g., including the second data block) in the second snapshot. 
     Alternatively, in some embodiments, once the second snapshot is generated for the virtual machine, it is transferred to the in-place recovery system  334  for block changes identification. Specifically, once system  334  determines data changes occurred between the first point in time and the second point in time, system  334  identifies block changes between the two snapshots. For example, system  334  identifies the data blocks (e.g., including the first data block) in the first snapshot that contains the original data content of the modified changes in the second block of the second snapshot. 
     At operation  510 , the in-place recovery system  334  generates the reverse incremental backup data (e.g., a reverse incremental file) to include the first data block. The reverse incremental data may include metadata that identifies the particular virtual machine to be recovered, the plurality of virtual machine configuration properties, and other data necessary to be included to allow the in-place virtual machine recovery. 
     At operation  512 , the in-place recovery system  334  restores the virtual machine in-place based on the reverse incremental backup data. The restored virtual machine is associated with the same set of configuration properties. Specifically, when restoring the virtual machine, the system simply writes the first data blocks to the disks of the virtual machine to be recovered to reverse the block changes after the first point in time when the first snapshot was generated. This way, the virtual machine is recovered in-place at the primary storage platform. Regardless of the size of the virtual machine, the time for recovery is linear to the number of data blocks changed. Further, no new virtual machine is created, that all configuration properties of the virtual machine are preserved. 
       FIG.  6    depicts a flowchart indicating example in-place virtual machine recovery operations in a method, according to some embodiments. The operations of process  600  may be performed by any number of different systems, such as the in-place recovery system  334  or the data management system  302  as described herein, or any portion thereof, such as a processor included in any of the systems. 
     The operation of process  600  is related to an embodiment of the in-place data recovery process where the virtual machine is disconnected when the second snapshot is taken and reconnected when the data restoration or recovery is completed. The operation of process  600  starts at operation  502 , followed by operation  504 , as discussed above. Following operation  504 , at operation  602 , the in-place recovery system  334  disconnects the virtual machine from the network in the primary storage platform or from a virtual power source. Disconnecting the virtual machine from the virtual power source may include shutting down the virtual machine following the shutdown procedure of the operating system installed in it. The purpose of disconnecting the virtual machine is to preserve the data at the time when the second snapshot is taken, so that no data changes will happen before system  334  completes the recovery process for the viral machine. 
     The operation  604  is followed by operations  506 ,  508 , and  510 , as discussed above. Following operation  510 , at operation  604 , system  334  restores the virtual machine in-place based on the reverse incremental data while the virtual machine is disconnected (e.g., offline) or shut down. At operation  606 , system  334  reconnects or turns on the virtual machine when all the data changes occurred after the first point in time has been reversed. 
       FIG.  7    depicts a block diagram illustrating a disk section of a virtual disk associated with a virtual machine, according to some embodiments. Row  1 , as shown in  FIG.  7   , includes a row of data blocks representing a portion of storage space in a virtual disk associated with the virtual machine for recovery. The first snapshot includes data or metadata referring to the data in the data blocks in Row  1 . Row  1 ′, as shown, includes data blocks of Row  1  after data changes after the first snapshot is generated. The second snapshot includes data or metadata referring to the data in the data blocks in Row  1 ′. For example, block  704  includes the data content of block  702  after data changes. Likewise, block  712  includes the data content of block  706  after data changes. 
     In some embodiments, upon identifying the first snapshot based on the user request, the in-place recovery system  334  generates or causes to generate the second snapshot. In one example, the block changes are identified at the primary storage platform using the third-party data block tracking service associated with the primary storage platform. For example, the third-party data block tracking service tracks all blocks changed (e.g., blocks  702 ,  706 ,  708 , and  710 ) between the first snapshot and the second snapshot. When the second snapshot is taken, the third-party data block tracking service may provide system  334  a record of all the blocks changed from the first snapshot corresponding to the first point in time and the second snapshot corresponding to the second point in time. Based on the record provided, system  334  may determine data blocks, such as blocks  702 ,  706 ,  708 , and  710 , in the first snapshot have been changed into the modified data blocks, such as blocks  704 ,  712 ,  714 , and  716 , in the second snapshot. System  334  may request the original data blocks  702 ,  706 ,  708 , and  710  in the first snapshot to be transferred to the virtual machine for data recovery. More data changes lead to longer recovery time. The in-place virtual machine recovery process is agnostic to the size of the virtual machine because the process identifies blocks changes and overwrites the changed blocks with the original blocks for recovery, rather than having to create a new virtual machine that involves a significant amount of data transfer. 
     In some embodiments, the data blocks are identified based on a block offset and a block length associated with the data block. For example, a block offset is the third block to the left. Therefore, the value of block offset for block  702  is identified as 2, provided that the default value of a block offset is 0. The block length of block  702  is 1, indicating one block, whereas the block length of blocks  702  and  706  is 2, indicating two blocks. The block offset and block length help identify the location of data in disks. System  334  may overwrite or causes to overwrite the corresponding data blocks to reverse the data changes during the in-place recovery process. 
       FIG.  8    is a block diagram  800  illustrating an architecture of software  802 , which can be installed on any one or more of the devices described above.  FIG.  8    is merely a non-limiting example of a software architecture, and it will be appreciated that many other architectures can be implemented to facilitate the functionality described herein. In various embodiments, the software  802  is implemented by hardware such as a machine  900  of  FIG.  9    that includes processor(s)  846 , memory  848 , and I/O components  850 . In this example architecture, the software  802  can be conceptualized as a stack of layers where each layer may provide a particular functionality. For example, the software  802  includes layers such as an operating system  804 , libraries  806 , frameworks  808 , and applications  810 . Operationally, the applications  810  invoke API calls  812  (application programming interface) through the software stack and receive messages  814  in response to the API calls  812 , consistent with some embodiments. 
     In various implementations, the operating system  804  manages hardware resources and provides common services. The operating system  804  includes, for example, a kernel  816 , services  818 , and drivers  820 . The kernel  816  acts as an abstraction layer between the hardware and the other software layers, consistent with some embodiments. For example, the kernel  816  provides memory management, processor management (e.g., scheduling), component management, networking, and security settings, among other functionality. The services  818  can provide other common services for the other software layers. The drivers  820  are responsible for controlling or interfacing with the underlying hardware, according to some embodiments. For instance, the drivers  820  can include display drivers, camera drivers, BLUETOOTH® or BLUETOOTH® Low Energy drivers, flash memory drivers, serial communication drivers (e.g., Universal Serial Bus (USB) drivers), WI-FI® drivers, audio drivers, power management drivers, and so forth. 
     In some embodiments, the libraries  806  provide a low-level common infrastructure utilized by the applications  810 . The libraries  806  can include system libraries  822  (e.g., C standard library) that can provide functions such as memory allocation functions, string manipulation functions, mathematic functions, and the like. In addition, the libraries  806  can include API libraries  824  such as media libraries (e.g., libraries to support presentation and manipulation of various media formats such as Moving Picture Experts Group-4 (MPEG4), Advanced Video Coding (H.264 or AVC), Moving Picture Experts Group Layer-3 (MP3), Advanced Audio Coding (AAC), Adaptive Multi-Rate (AMR) audio codec, Joint Photographic Experts Group (JPEG or JPG), or Portable Network Graphics (PNG)), graphics libraries (e.g., an OpenGL framework used to render in two dimensions (2D) and three dimensions (3D) in a graphic content on a display), database libraries (e.g., SQLite to provide various relational database functions), web libraries (e.g., WebKit to provide web browsing functionality), and the like. The libraries  806  can also include a wide variety of other libraries  826  to provide many other APIs to the applications  810 . 
     The frameworks  808  provide a high-level common infrastructure that can be utilized by the applications  810 , according to some embodiments. For example, the frameworks  808  provide various graphical user interface (GUI) functions, high-level resource management, high-level location services, and so forth. The frameworks  808  can provide a broad spectrum of other APIs that can be utilized by the applications  810 , some of which may be specific to a particular operating system or platform. 
     In an embodiment, the applications  810  include built-in applications  828  and a broad assortment of other applications, such as a third-party application  844 . The built-in applications  828  may include a home application, a contacts application, a browser application, a book reader application, a location application, a media application, a messaging application, a game application. According to some embodiments, the applications  810  are programs that execute functions defined in the programs. Various programming languages can be employed to create one or more of the applications  810 , structured in a variety of manners, such as object-oriented programming languages (e.g., Objective-C, Java, or C++) or procedural programming languages (e.g., C or assembly language). In a specific example, the third-party application  844  (e.g., an application developed using the ANDROID™ or IOS™ software development kit (SDK) by an entity other than the vendor of the particular platform) may be mobile software running on a mobile operating system such as IOS™, ANDROID™, WINDOWS® Phone, or another mobile operating system. In this example, the third-party application  844  can invoke the API calls  812  provided by the operating system  804  to facilitate functionality described herein. 
       FIG.  9    illustrates a diagrammatic representation of a machine  900  in the form of a computer system within which a set of instructions may be executed for causing the machine to perform any one or more of the methodologies discussed herein, according to some embodiments. Specifically,  FIG.  9    shows a diagrammatic representation of the machine  900  in the example form of a computer system, within which instructions  906  (e.g., software, a program, an application, an applet, an app, or other executable code) for causing the machine  900  to perform any one or more of the methodologies discussed herein may be executed. Additionally, or alternatively, the instructions  906  may implement the operations of the methods shown in  FIGS.  5  and  6   , or as elsewhere described herein. 
     The instructions  906  transform the general, non-programmed machine  900  into a particular machine  900  programmed to carry out the described and illustrated functions in the manner described. In alternative embodiments, the machine  900  operates as a standalone device or may be coupled (e.g., networked) to other machines. In a networked deployment, the machine  900  may operate in the capacity of a server machine or a client machine in a server-client network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine  900  may comprise, but not be limited to, a server computer, a client computer, a personal computer (PC), a tablet computer, a laptop computer, a netbook, a set-top box (STB), a PDA, an entertainment media system, a cellular telephone, a smart phone, a mobile device, a wearable device (e.g., a smart watch), a smart home device (e.g., a smart appliance), other smart devices, a web appliance, a network router, a network switch, a network bridge, or any machine capable of executing the instructions  906 , sequentially or otherwise, that specify actions to be taken by the machine  900 . Further, while only a single machine  900  is illustrated, the term “machine” shall also be taken to include a collection of machines  900  that individually or jointly execute the instructions  906  to perform any one or more of the methodologies discussed herein. 
     The machine  900  may include processor(s)  846 , memory  848 , and I/O components  850 , which may be configured to communicate with each other such as via a bus  902 . In some embodiments, the processor(s)  846  (e.g., a Central Processing Unit (CPU), a Reduced Instruction Set Computing (RISC) processor, a Complex Instruction Set Computing (CISC) processor, a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP), an ASIC, a Radio-Frequency Integrated Circuit (RFIC), another processor, or any suitable combination thereof) may include, for example, a processor  904  and a processor  908  that may execute the instructions  906 . The term “processor” is intended to include multi-core processors that may comprise two or more independent processors (sometimes referred to as “cores”) that may execute instructions contemporaneously. Although  FIG.  9    shows multiple processor(s)  846 , the machine  900  may include a single processor with a single core, a single processor with multiple cores (e.g., a multi-core processor), multiple processors with a single core, multiple processors with multiples cores, or any combination thereof. 
     The memory  848  may include a main memory  910 , a static memory  912 , and a storage unit  914 , each accessible to the processor(s)  846  such as via the bus  902 . The main memory  910 , the static memory  912 , and storage unit  914  store the instructions  906  embodying any one or more of the methodologies or functions described herein. The instructions  906  may also reside, completely or partially, within the main memory  910 , within the static memory  912 , within the storage unit  914 , within at least one of the processor(s)  846  (e.g., within the processor&#39;s cache memory), or any suitable combination thereof, during execution thereof by the machine  900 . 
     The I/O components  850  may include a wide variety of components to receive input, provide output, produce output, transmit information, exchange information, capture measurements, and so on. The specific I/O components  850  that are included in a particular machine will depend on the type of machine. For example, portable machines such as mobile phones will likely include a touch input device or other such input mechanisms, while a headless server machine will likely not include such a touch input device. It will be appreciated that the I/O components  850  may include many other components that are not shown in  FIG.  9   . The I/O components  850  are grouped according to functionality merely for simplifying the following discussion and the grouping is in no way limiting. In some embodiments, the I/O components  850  may include output components  918  and input components  920 . The output components  918  may include visual components (e.g., a display such as a plasma display panel (PDP), a light emitting diode (LED) display, a liquid crystal display (LCD), a projector, or a cathode ray tube (CRT)), acoustic components (e.g., speakers), haptic components (e.g., a vibratory motor, resistance mechanisms), other signal generators, and so forth. The input components  920  may include alphanumeric input components (e.g., a keyboard, a touch screen configured to receive alphanumeric input, a photo-optical keyboard, or other alphanumeric input components), point-based input components (e.g., a mouse, a touchpad, a trackball, a joystick, a motion sensor, or another pointing instrument), tactile input components (e.g., a physical button, a touch screen that provides location and/or force of touches or touch gestures, or other tactile input components), audio input components (e.g., a microphone), and the like. 
     In some embodiments, the I/O components  850  may include biometric components  922 , motion components  924 , environmental components  926 , or position components  928 , among a wide array of other components. For example, the biometric components  922  may include components to detect expressions (e.g., hand expressions, facial expressions, vocal expressions, body gestures, or eye tracking), measure biosignals (e.g., blood pressure, heart rate, body temperature, perspiration, or brain waves), identify a person (e.g., voice identification, retinal identification, facial identification, fingerprint identification, or electroencephalogram-based identification), and the like. The motion components  924  may include acceleration sensor components (e.g., accelerometer), gravitation sensor components, rotation sensor components (e.g., gyroscope), and so forth. The environmental components  926  may include, for example, illumination sensor components (e.g., photometer), temperature sensor components (e.g., one or more thermometers that detect ambient temperature), humidity sensor components, pressure sensor components (e.g., barometer), acoustic sensor components (e.g., one or more microphones that detect background noise), proximity sensor components (e.g., infrared sensors that detect nearby objects), gas sensors (e.g., gas detection sensors to detection concentrations of hazardous gases for safety or to measure pollutants in the atmosphere), or other components that may provide indications, measurements, or signals corresponding to a surrounding physical environment. The position components  928  may include location sensor components (e.g., a GPS receiver component), altitude sensor components (e.g., altimeters or barometers that detect air pressure from which altitude may be derived), orientation sensor components (e.g., magnetometers), and the like. 
     Communication may be implemented using a wide variety of technologies. The I/O components  850  may include communication components  930  operable to couple the machine  900  to a network  936  or devices  932  via a coupling  938  and a coupling  934 , respectively. For example, the communication components  930  may include a network interface component or another suitable device to interface with the network  936 . In further examples, the communication components  930  may include wired communication components, wireless communication components, cellular communication components, Near Field Communication (NFC) components, Bluetooth® components (e.g., Bluetooth® Low Energy), Wi-Fi® components, and other communication components to provide communication via other modalities. The devices  932  may be another machine or any of a wide variety of peripheral devices (e.g., a peripheral device coupled via a USB). 
     Moreover, the communication components  930  may detect identifiers or include components operable to detect identifiers. For example, the communication components  930  may include Radio Frequency Identification (RFID) tag reader components, NFC smart tag detection components, optical reader components (e.g., an optical sensor to detect one-dimensional bar codes such as Universal Product Code (UPC) bar code, multi-dimensional bar codes such as Quick Response (QR) code, Aztec code, Data Matrix, Dataglyph, MaxiCode, PDF417, Ultra Code, UCC RSS-2D bar code, and other optical codes), or acoustic detection components (e.g., microphones to identify tagged audio signals). In addition, a variety of information may be derived via the communication components  930 , such as location via Internet Protocol (IP) geolocation, location via Wi-Fi® signal triangulation, location via detecting an NFC beacon signal that may indicate a particular location, and so forth. 
     The various memories (i.e., memory  848 , main memory  910 , and/or static memory  912 ) and/or storage unit  914  may store one or more sets of instructions and data structures (e.g., software) embodying or utilized by any one or more of the methodologies or functions described herein. These instructions (e.g., the instructions  906 ), when executed by processor(s)  846 , cause various operations to implement the disclosed embodiments. 
     As used herein, the terms “machine-storage medium,” “device-storage medium,” “computer-storage medium” mean the same thing and may be used interchangeably in this disclosure. The terms refer to a single or multiple storage devices and/or media (e.g., a centralized or distributed database, and/or associated caches and servers) that store executable instructions and/or data. The terms shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media, including memory internal or external to processors. Specific examples of machine-storage media, computer-storage media and/or device-storage media include non-volatile memory, including by way of example semiconductor memory devices, e.g., erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), FPGA, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The terms “machine-storage media,” “computer-storage media,” and “device-storage media” specifically exclude carrier waves, modulated data signals, and other such media, at least some of which are covered under the term “signal medium” discussed below. 
     In some embodiments, one or more portions of the network  936  may be an ad hoc network, an intranet, an extranet, a VPN, a LAN, a WLAN, a WAN, a WWAN, a MAN, the Internet, a portion of the Internet, a portion of the PSTN, a plain old telephone service (POTS) network, a cellular telephone network, a wireless network, a Wi-Fi® network, another type of network, or a combination of two or more such networks. For example, the network  936  or a portion of the network  936  may include a wireless or cellular network, and the coupling  938  may be a Code Division Multiple Access (CDMA) connection, a Global System for Mobile communications (GSM) connection, or another type of cellular or wireless coupling. In this example, the coupling  938  may implement any of a variety of types of data transfer technology, such as Single Carrier Radio Transmission Technology (1xRTT), Evolution-Data Optimized (EVDO) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for GSM Evolution (EDGE) technology, third Generation Partnership Project (3GPP) including 3G, fourth generation wireless (4G) networks, Universal Mobile Telecommunications System (UMTS), High Speed Packet Access (HSPA), Worldwide Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE) standard, others defined by various standard-setting organizations, other long range protocols, or other data transfer technology. 
     The instructions  906  may be transmitted or received over the network  936  using a transmission medium via a network interface device (e.g., a network interface component included in the communication components  930 ) and utilizing any one of a number of well-known transfer protocols (e.g., hypertext transfer protocol (HTTP)). Similarly, the instructions  906  may be transmitted or received using a transmission medium via the coupling  934  (e.g., a peer-to-peer coupling) to the devices  932 . The terms “non-transitory computer-readable storage medium,” “transmission medium” and “signal medium” mean the same thing and may be used interchangeably in this disclosure. The terms “transmission medium” and “signal medium” shall be taken to include any intangible medium that is capable of storing, encoding, or carrying the instructions  906  for execution by the machine  900 , and includes digital or analog communications signals or other intangible media to facilitate communication of such software. Hence, the terms “transmission medium” and “signal medium” shall be taken to include any form of modulated data signal, carrier wave, and so forth. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a matter as to encode information in the signal. 
     The terms “machine-readable medium,” “computer-readable medium” and “device-readable medium” mean the same thing and may be used interchangeably in this disclosure. The terms are defined to include both machine-storage media and transmission media. Thus, the terms include both storage devices/media and carrier waves/modulated data signals. 
     Although examples have been described with reference to some embodiments or methods, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader scope of the embodiments. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings that form a part hereof, show by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. 
     Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.