Patent Application
20230169036
Snapshot technology is commonly used to preserve point-in-time (PIT) state and data of a virtual computing instance (VCI), such as a virtual machine. Snapshots of VCIs are used for various applications, such as VCI replication, VCI rollback and data protection for backup and recovery.
Current snapshot technology can be classified into two types of snapshot techniques. The first type of snapshot techniques includes redo-log based snapshot techniques, which involve maintaining changes for each snapshot in separate redo logs. A concern with this approach is that the snapshot technique cannot be scaled to manage a large number of snapshots, for example, hundreds of snapshots. In addition, this approach requires intensive computations to consolidate across different snapshots.
The second type of snapshot techniques includes tree-based snapshot techniques, which involve creating a chain or series of snapshots to maintain changes to the underlying data using a B tree structure, such as a B+ tree structure. Significant advantage of the tree-based snapshot techniques over the redo-log based snapshot techniques is the scalability of the tree-based snapshot techniques. However, the snapshot B tree structures of the tree-based snapshot techniques may include many nodes that are shared by multiple snapshots. Thus, physical extents in physical storage where the nodes of the snapshot B tree structures are written may be shared by multiple snapshots. Consequently, the physical extents for the snapshot B tree structures need to be efficiently managed, especially when the snapshots are selectively deleted.
Throughout the description, similar reference numbers may be used to identify similar elements.
As used herein, the term “virtual computing instance” refers to any software processing entity that can run on a computer system, such as a software application, a software process, a virtual machine or a virtual container. A virtual machine is an emulation of a physical computer system in the form of a software computer that, like a physical computer, can run an operating system and applications. A virtual machine may be comprised of a set of specification and configuration files and is backed by the physical resources of the physical host computer. A virtual machine may have virtual devices that provide the same functionality as physical hardware and have additional benefits in terms of portability, manageability, and security. An example of a virtual machine is the virtual machine created using VMware vSphere® solution made commercially available from VMware, Inc of Palo Alto, California. A virtual container is a package that relies on virtual isolation to deploy and run applications that access a shared operating system (OS) kernel. An example of a virtual container is the virtual container created using a Docker engine made available by Docker, Inc. In this disclosure, the virtual computing instances will be described as being virtual machines, although embodiments of the invention described herein are not limited to virtual machines (VMs).
The cluster management server 108 of the distributed storage system 100 operates to manage and monitor the cluster 106 of host computers 104. The cluster management server 108 may be configured to allow an administrator to create the cluster 106, add host computers to the cluster and delete host computers from the cluster. The cluster management server 108 may also be configured to allow an administrator to change settings or parameters of the host computers in the cluster regarding the VSAN 102, which is formed using the local storage resources of the host computers in the cluster. The cluster management server 108 may further be configured to monitor the current configurations of the host computers and any VCIs running on the host computers, for example, VMs. The monitored configurations may include hardware and/or software configurations of each of the host computers. The monitored configurations may also include VCI hosting information, i.e., which VCIs (e.g., VMs) are hosted or running on which host computers. The monitored configurations may also include information regarding the VCIs running on the different host computers in the cluster.
The cluster management server 108 may also perform operations to manage the VCIs and the host computers 104 in the cluster 106. As an example, the cluster management server 108 may be configured to perform various resource management operations for the cluster, including VCI placement operations for either initial placement of VCIs and/or load balancing. The process for initial placement of VCIs, such as VMs, may involve selecting suitable host computers for placement of the virtual instances based on, for example, memory and central processing unit (CPU) requirements of the VCIs, the current memory and CPU loads on all the host computers in the cluster, and the memory and CPU capacity of all the host computers in the cluster.
In some embodiments, the cluster management server 108 may be a physical computer. In other embodiments, the cluster management server may be implemented as one or more software programs running on one or more physical computers, such as the host computers 104 in the cluster 106, or running on one or more VCIs, which may be hosted on any host computers. In an implementation, the cluster management server is a VMware vCenter™ server with at least some of the features available for such a server.
As illustrated in
The hypervisor 112 of each host computer 104, which is a software interface layer, enables sharing of the hardware resources of the host computer by VMs 124, running on the host computer using virtualization technology. With the support of the hypervisor 112, the VMs provide isolated execution spaces for guest software. In other embodiments, the hypervisor may be replaced with an appropriate virtualization software to support a different type of VCIs.
The VSAN module 114 of each host computer 104 provides access to the local storage resources of that host computer (e.g., handle storage input/output (I/O) operations to data objects stored in the local storage resources as part of the VSAN 102) by other host computers 104 in the cluster 106 or any software entities, such as VMs 124, running on the host computers in the cluster. As an example, the VSAN module of each host computer allows any VM running on any of the host computers in the cluster to access data stored in the local storage resources of that host computer, which may include virtual disks (or portions thereof) of VMs running on any of the host computers and other related files of those VMs. In addition, the VSAN module generates and manages snapshots of storage objects, such as virtual disk files of the VMs, in an efficient manner.
In an embodiment, the VSAN module 114 leverages B tree structures, such as copy-on-write (COW) B+ tree structures, to organize storage objects and their snapshots taken at different times. An example of a COW B+ tree structure for one storage object managed by the VSAN module 114 in accordance with an embodiment of the invention is illustrated in
When a modification of the storage object is made, after the first snapshot SS1 is created, a new root node and one or more index and leaf nodes are created. In
In
In
In this manner, multiple snapshots of a storage object can be created at different times. These multiple snapshots create a hierarchy of snapshots.
As more COW B+ tree snapshots are created for a storage object, e.g., a virtual disk of a virtual machine, more nodes are shared by the various snapshots. The nodes of the COW B+ tree structure, including the shared nodes, are stored in physical extents, which are one or more contiguous data blocks of physical storage, such as physical disks. Thus, the same physical extents may be shared by multiple snapshots. When a snapshot is being deleted, the physical extents associated with the snapshot, i.e., accessible to the snapshot, may be removed depending on the sharing status of the physical extents, as described below.
In an embodiment, as illustrated in
In an embodiment, the logical maps and middle logical map may be stored in B tree structures. In a particular implementation, the logical maps are stored in a COW B+ tree structure, as illustrated in
In some embodiments, a performance-efficient method is used to manage the shared status of physical extents in the distributed storage system 100. In these embodiments, each physical extent is assigned with a monotonically increased sequence value, e.g., a monotonically increased sequence number, which is used as extent ownership value. In some embodiments, MBA values are used as the extent ownership values, as described herein. However, in other embodiments, the extent ownership values may be any monotonically increased sequence values, which are assigned to or associated with the physical extents. In some embodiments, the monotonically increased sequence values may include alphanumeric characters or exclusively numbers. In the embodiments where MBA values are used as extent ownership values, each snapshot is assigned with a minimum extent ownership value, i.e., minMBA, the minimum MBA of all physical extents owned by the snapshot. In addition, each physical extent has the following property: the physical extent accessible to a snapshot and whose physical extent MBA is smaller than the minMBA of the snapshot is shared between the snapshot and its parent snapshot. Relying on this property, the system can quickly determine the shared status of a physical extent to be overwritten for write requests at the running point (i.e., the current state of a storage object). Unshared physical extents are reused for updates. However, shared physical extents are copied out first to new physical extents, which are then used for updates. This approach is more performance efficient than some state-of-art methods, such as shared bits, to manage the shared status of physical extents since no input/output (IO) is required to update the shared status of each physical extent individually.
When deleting a snapshot, the physical extents exclusively owned by the snapshot can be removed. Physical extents shared with the child snapshot may be unlinked from the snapshot being deleted, but the physical extents themselves should be kept for the child snapshot. For the shared physical extents that have been unlinked from the snapshot being deleted, these physical extents cannot be updated in-place since the physical extents are needed as is for the child snapshot. Thus, in order to update these extents, new physical extents should be created for modification. However, there is a problem when the parent snapshot of the running point is being deleted with respect to the physical extents shared between the parent snapshot and the running point. Unlike the other unlinked shared physical extents, parent snapshot physical extents shared with the running point that have been unlinked should be reused for updates, i.e., updated in-place rather than a new physical extent being created. Thus, there is a need to identify shared physical extents that have been unlinked from the parent snapshot of the running point for deletion of the parent snapshot.
In the distributed storage system 100, the snapshot manager 400 of each VSAN module 114 in the respective host computer 104 is able to properly manage shared physical extents that have been unlinked from the parent snapshot of the running point of a storage object, which is being handled by that VSAN module, when the parent snapshot is being deleted. In an embodiment, when the snapshot manager starts to delete the parent snapshot of the running point of a storage object, the snapshot manager will transfer the ownership of all physical extents owned by the parent snapshot to the running point immediately. This is achieved by updating the minMBA of the running point to the minMBA of the parent snapshot. After the ownership of all physical extents previously owned by the parent snapshot is transferred to the running point, any overwrite related to such physical extents at the running point will be executed in-place.
For the physical extents of the parent snapshot being deleted, the snapshot manager checks whether the physical extents are exclusively accessible to the parent snapshot. In an embodiment, all physical extents exclusively accessible to the parent snapshot can be checked efficiently by iterating all physical extents in the snapshot logical map and the running point logical map in parallel to find the difference. A physical extent is exclusively accessible to the parent snapshot if the extent ownership value assigned to the physical extent, e.g., MBA of the physical extent, is only found in the snapshot logical map. Thus, a physical extent is not exclusively accessible to the parent snapshot if the extent ownership value assigned to the physical extent is found in both the snapshot logical map and the running point logical map. Each physical extent accessible to the parent snapshot but not accessible to the running point needs to be removed in the course of the snapshot physical deletion. These physical extents are not accessible to the running point (namely, these physical extents are exclusively owned by the parent snapshot) and cannot be accessed for any client request, so it is safe to delete the physical extent. For the physical extent that is accessible to both the running point and the parent snapshot, the snapshot manager will just leave the physical extent as it is since this physical extent is already owned by the running point and its lifecycle will be managed by the running point. In this way, physical extents exclusively owned by the parent snapshot being deleted are removed and the logical map of the running point is kept intact. This deletion operation of the parent snapshot of the running point of a storage object is described in more detail below.
An operation executed by a particular snapshot manager 400 in the distributed storage system 100 to delete the parent snapshot of the running point of a storage object in accordance with an embodiment is described with reference to a process flow diagram of
The operation begins at step 502, where a request for deletion of the parent snapshot of the running point of the storage object is received at the snapshot manager 400. The deletion request may have originated from a user input or a software process running on any of the host computers 104 in the storage system 100. In an embodiment, the cluster manager server 108 may be used to enter the deletion request by the user, such as an administrator.
Next, at step 504, the minMBA of the running point is updated to the minMBA of the parent snapshot by the snapshot manager 400. That is, the minMBA of the running point is changed from its previous value to the minMBA of the parent snapshot. As a result, any physical extent with an MBA value equal to or greater than the new minMBA value of the running point will be deemed to be owned by the running point. Thus, if any logical block is overwritten that has an MBA value equal to or larger than the new minMBA value of the running point, the physical extent corresponding to the logical block is reused. However, if any logical block is overwritten that has an MBA value smaller than the new minMBA value of the running point, the physical extent is copied to a new physical extent and the new physical extent is updated.
Next, at step 506, a target logical block of the parent snapshot is selected for deletion by the snapshot manager 400. In an embodiment, the target logical block may be selected based on an order of increasing or decreasing block numbers, e.g., LBAs. Thus, if the logical block is selected based on an order of increasing block numbers, the logical block of the parent snapshot with the lowest block number that has not yet been processed for deletion is selected. In another embodiment, the target logical block may be randomly selected from the logical blocks of the parent snapshot that have not yet been processed for deletion.
Next, at step 508, a determination is made by the snapshot manager 400 whether the physical extent corresponding to the target logical block is exclusively accessible to the parent snapshot. In an embodiment, this determination can be efficiently made by iterating through all MBAs, which are assigned to the physical extents, in the parent snapshot logical map and the running point logical map in parallel to find MBAs that are only in the parent snapshot logical map. That is, if an MBA is found only in the parent snapshot logical map, then the physical extent assigned to that MBA is exclusively accessible to the parent snapshot.
If the physical extent corresponding to the target logical block is exclusively accessible to the parent snapshot, the operation proceeds to step 510, where the physical extent corresponding to the target logical block is deleted, e.g., all data in the physical extent is actually deleted or may be considered to have been deleted. Any physical extent accessible to the parent snapshot of the running point but not accessible to the running point needs to be removed in the course of the deletion of the parent snapshot. These physical extents are not accessible to the running point and cannot be accessed for any client request. Thus, it is safe to delete such physical extents.
However, if the physical extent corresponding to the target logical block is not exclusively accessible to the parent snapshot, i.e., shared by both the parent snapshot and the running point, the operation proceeds to step 512, where no action is taken on the physical extent corresponding to the target logical block, i.e., the physical extent is left as is. Such physical extent is already owned by the running point, and thus, its lifecycle will be managed by the running point. Thus, the physical extent will be reused for any updates by the running point.
Next, at step 514, a determination is made by the snapshot manager 400 whether the current logical block being processed is the last logical block of the parent snapshot. If no, then the operation proceeds back to step 508 to select the next logical block of the parent snapshot of the running point to process. However, if the current logical block is the last logical block of the parent snapshot, then the operation comes to an end.
In other embodiments, rather than processing one logical block of the parent snapshot of the running point of the storage object at a time, multiple logical blocks of the parent snapshot of the running point may be processed in parallel to delete physical extents that correspond to the logical blocks that are only accessible to the parent snapshot of the running point. In other embodiments, all the logical blocks of the parent snapshot of the running point that are only accessible to the parent snapshot of the running point may be found first and then the physical extents that correspond to those logical blocks may be deleted.
The deletion operation of the parent snapshot of the running point of a storage object is further described using an example with the following layout of physical extents for the running point and its parent snapshot at t=T0:
In this example, four logical blocks of the running point and its parent snapshot, i.e., block 0, block 1, block 2 and block 3, are illustrated with physical extent associations, if any. Also, in this example, the minMBA of the parent snapshot is M0, and the minMBA of the running point is M4. As shown in the above table, blocks 0, 1, 2 and 3 were written at the parent snapshot with middle block addresses (MBAs) M0, M1, M2 and M3, respectively. As used herein, [Mx] means that the block was written and associated with the mapping extent Mx, and [--] means that the block has not been written at the parent snapshot or the running point. Thus, in this example, MBAs are used as the extent ownership values.
The logical map of the parent snapshot maintains the mapping between each logical block and its MBA (which is mapped to a corresponding PBA) for the four (4) written blocks. The logical map of the running point also contains the mapping between each logical block and its MBA (which is also mapped to a corresponding PBA) for these four (4) written blocks.
At t=T1, the logical block 0 is overwritten in the running point. The logical block 0 has an MBA value of M0, which is smaller than the minMBA of the running point, which is M4. Thus, the block 0 is shared by the running point and its parent snapshot, and a new physical extent associated with M4 is created to hold the mapping for data of the logical block 0. As a result, M4 will be referenced in the logical map of the running point instead of M0, as illustrated in the following table.
This process of overwriting the logical block 0 can be illustrated using examples of logical maps of the running point and its parent snapshot. In this example, before creating the physical extent associated with M4, the logical maps of the parent snapshot and the running point are as follows:
At t=T2, the snapshot manager for the storage object starts to delete the parent snapshot of the running point in response to an instruction to delete the parent snapshot, which may be initiated by a user or a process running in the distributed storage system 100. As a result, the minMBA of the running point is updated to M0 from M4. However, the layout of the extents for the parent snapshot and the running point has not changed, as illustrated in the following table.
At t=T3, the logical block 1 of the parent snapshot is overwritten. In this scenario, since the MBA value of M1 for the block 1 is larger than the minMBA of the running point, which is M0, the block 1 is deemed to be owned by the running point and the extent with M1 is reused, as illustrated in the following table.
At t=T4, the snapshot manager starts to process the first logical block of the parent snapshot, i.e., the logical block 0, to determine whether the physical extent mapped to the logical block should be removed or not. Since the physical extent with M0 for the logical block 0 is not accessible to the running point, i.e., exclusively accessible to the parent snapshot being deleted, the physical extent with M0 will be removed, as illustrated in the following table.
At t=T5, the snapshot manager starts to process the rest of the logical blocks of the parent snapshot, i.e., the logical blocks 1, 2 and 3, to determine whether these block should be removed or not. Since the physical extents with M1, M2 and M3 for the logical blocks 1, 2 and 3 are accessible to the running point, i.e., not exclusively accessible to the parent snapshot being deleted, these physical data blocks will be left alone as is, i.e., the physical extents will not be removed, as illustrated in the following table.
Turning now to
The CLOM 602 operates to validate storage resource availability, and the DOM 604 operates to create components and apply configuration locally through the LSOM 606. The DOM 604 also operates to coordinate with counterparts for component creation on other host computers 104 in the cluster 106. All subsequent reads and writes to storage objects funnel through the DOM 604, which will take them to the appropriate components. The LSOM 606 operates to monitor the flow of storage I/O operations to the local storage 122, for example, to report whether a storage resource is congested. The CMMDS 608 is responsible for monitoring the VSAN cluster’s membership, checking heartbeats between the host computers in the cluster, and publishing updates to the cluster directory. Other software components use the cluster directory to learn of changes in cluster topology and object configuration. For example, the DOM uses the contents of the cluster directory to determine the host computers in the cluster storing the components of a storage object and the paths by which those host computers are reachable.
The RDT manager 610 is the communication mechanism for storage-related data or messages in a VSAN network, and thus, can communicate with the VSAN modules 114 in other host computers 104 in the cluster 106. As used herein, storage-related data or messages (simply referred to herein as “messages”) may be any pieces of information, which may be in the form of data streams, that are transmitted between the host computers 104 in the cluster 106 to support the operation of the VSAN 102. Thus, storage-related messages may include data being written into the VSAN 102 or data being read from the VSAN 102. In an embodiment, the RDT manager uses the Transmission Control Protocol (TCP) at the transport layer and it is responsible for creating and destroying on demand TCP connections (sockets) to the RDT managers of the VSAN modules in other host computers in the cluster. In other embodiments, the RDT manager may use remote direct memory access (RDMA) connections to communicate with the other RDT managers.
As illustrated in
A computer-implemented method for deleting parent snapshots of running points of storage objects stored in a storage system in accordance with an embodiment of the invention is described with reference to a flow diagram of
The components of the embodiments as generally described in this document and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.
Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.
Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
Although the operations of the method(s) herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be implemented in an intermittent and/or alternating manner.
It should also be noted that at least some of the operations for the methods may be implemented using software instructions stored on a computer useable storage medium for execution by a computer. As an example, an embodiment of a computer program product includes a computer useable storage medium to store a computer readable program that, when executed on a computer, causes the computer to perform operations, as described herein.
Furthermore, embodiments of at least portions of the invention can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
The computer-useable or computer-readable medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device), or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disc, and an optical disc. Current examples of optical discs include a compact disc with read only memory (CD-ROM), a compact disc with read/write (CD-R/W), a digital video disc (DVD), and a Blu-ray disc.
In the above description, specific details of various embodiments are provided. However, some embodiments may be practiced with less than all of these specific details. In other instances, certain methods, procedures, components, structures, and/or functions are described in no more detail than to enable the various embodiments of the invention, for the sake of brevity and clarity.
Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.
