CONSISTENT UNMAPPING OF APPLICATION DATA IN PRESENCE OF CONCURRENT, UNQUIESCED WRITERS AND READERS

• US 20120331242A1
• Filed: 06/22/2011
• Published: 12/27/2012
• Est. Priority Date: 06/22/2011
• Status: Active Grant

• Current Assignee: Vmware LLC (Broadcom, Inc.)
• Original Assignee: VMware, Inc. (Broadcom, Inc.)
• Inventors: SHAIKH, Faraz, VILAYANNUR, Murali, VAGHANI, Satyam B., JOSHI, Kiran
• Granted Patent: US 9,146,766 B2
• Time in Patent Office: Days
• US Class Current: 711/154
• CPC Class Codes: G06F 12/0253 Garbage collection, i.e. reclamation of unreferenced memory
• CPC Class Codes: G06F 12/0261 using reference counting
• CPC Class Codes: G06F 12/0269 Incremental or concurrent garbage collection, e.g. in real-time systems G06F12/0261 takes precedence
• CPC Class Codes: G06F 12/0276 Generational garbage collection
• CPC Class Codes: G06F 16/1727 Details of free space management performed by the file system saving storage space on storage systems G06F3/0608; management of blocks in storage devices G06F3/064
• CPC Class Codes: G06F 16/182 Distributed file systems
• CPC Class Codes: G06F 16/188 Virtual file systems
• CPC Class Codes: G06F 2009/45579 I/O management, e.g. providing access to device drivers or storage
• CPC Class Codes: G06F 2212/1044 Space efficiency improvement
• CPC Class Codes: G06F 2212/154 Networked environment
• CPC Class Codes: G06F 3/0608 Saving storage space on storage systems
• CPC Class Codes: G06F 3/0631 by allocating resources to storage systems
• CPC Class Codes: G06F 3/0652 Erasing, e.g. deleting, data cleaning, moving of data to a wastebasket
• CPC Class Codes: G06F 3/0665 at area level, e.g. provisioning of virtual or logical volumes
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]
• CPC Class Codes: G06F 9/45533 Hypervisors; Virtual machine monitors
• CPC Class Codes: G06F 9/45558 Hypervisor-specific management and integration aspects

Abstract

Free storage blocks previously allocated to a logical block device are released back to an underlying storage system supporting the logical block device in a manner that does not conflict with write operations that may be issued to the free storage blocks at about the same time. According to a first technique, write operations on the same storage blocks to be released are paused until the underlying storage system has completed the releasing operation or, if the write operations are issued earlier than when the underlying storage system actually performs the releasing operation, such storage blocks are not released. According to a second technique, a special file is allocated the free storage blocks, which are then made available for safe releasing.

Claims

1. A method for releasing free storage blocks previously allocated to a logical block device back to an underlying storage system supporting the logical block device, comprising:

receiving a notification from a first process of a processing entity accessing the logical block device of an intent to request a release of a set of storage blocks that are currently allocated to the logical block device but that are not being used by the logical block device, wherein the notification identifies an initial set of storage blocks to be released;

intercepting a write operation from a second process of the processing entity;

determining that the write operation corresponds to a subset of the initial set of storage blocks;

issuing the write operation to the logical block device;

receiving from the first process a request to release a set of storage blocks from the logical block device, wherein the request identifies an updated set of storage blocks; and

releasing storage blocks in the updated set that are not in the subset of storage blocks corresponding to the write operation.

2. The method of claim 1, wherein the logical block device is thinly provisioned by the underlying storage system.

3. The method of claim 2, further comprising:

receiving a second write operation from a third process of the processing entity;

determining that the second write operation pertains to storage blocks identified in the issued request to the logical block device;

waiting for a completion of the releasing of the storage blocks identified in the issued request; and

issuing the second write operation to the logical block device, whereby the underlying storage system dynamically allocates storage blocks back to the logical block device to satisfy the second write operation.

4. The method of claim 3, wherein the first process identifies the initial set of storage blocks by requesting identification of free blocks from a file system of the logical block device and identifies the updates set of storage blocks.

5. The method of claim 4, wherein the first process identifies the updated set of storage blocks by requesting identification of free blocks from the file system of the logical block device and pruning the storage blocks in the initial set that are no longer free.

6. The method of claim 1, wherein the logical block device is a virtual disk, the underlying storage system is a logical unit number (LUN) of a networked storage system, and the processing entity is a virtual machine.

7. A non-transitory computer readable storage medium comprising instructions executable in a computer system to cause the computer system to carry out a method for releasing free storage blocks previously allocated to a logical block device back to an underlying storage system supporting the logical block device, said method comprising:

receiving a notification from a first process of a processing entity accessing the logical block device of an intent to request a release of a set of storage blocks that are currently allocated to the logical block device but that are not being used by the logical block device, wherein the notification identifies an initial set of storage blocks to be released;

intercepting a write operation from a second process of the processing entity;

determining that the write operation corresponds to a subset of the initial set of storage blocks;

issuing the write operation to the logical block device;

receiving from the first process a request to release a set of storage blocks from the logical block device, wherein the request identifies an updated set of storage blocks; and

releasing storage blocks in the updated set that are not in the subset of storage blocks corresponding to the write operation.

8. The non-transitory computer readable storage medium of claim 7, wherein the logical block device is thinly provisioned by the underlying storage system.

9. The non-transitory computer readable storage medium of claim 8, wherein the method further comprises:

receiving a second write operation from a third process of the processing entity;

determining that the second write operation pertains to storage blocks identified in the issued request to the logical block device;

waiting for a completion of the releasing of the storage blocks identified in the issued request; and

issuing the second write operation to the logical block device, whereby the underlying storage system dynamically allocates storage blocks back to the logical block device to satisfy the second write operation.

10. The non-transitory computer readable storage medium of claim 9, wherein the first process identifies the initial set of storage blocks by requesting identification of free blocks from a file system of the logical block device and identifies the updates set of storage blocks.

11. The non-transitory computer readable storage medium of claim 10, wherein the first process identifies the updated set of storage blocks by requesting identification of free blocks from the file system of the logical block device and pruning the storage blocks in the initial set that are no longer free.

12. The non-transitory computer readable storage medium of claim 7, wherein the logical block device is a virtual disk, the underlying storage system is a logical unit number (LUN) of a networked storage system, and the processing entity is a virtual machine.

13. A method for issuing a command to release free storage blocks previously allocated to a logical block device back to an underlying storage system supporting the logical block device, comprising:

identifying a set of free blocks to be released;

updating the set of free blocks to remove those free blocks that have already been released;

allocating the free blocks in the updated set to a file; and

issuing a command to release the free blocks allocated to the file.

14. The method of claim 13, further comprising:

maintaining a data structure to track blocks for which the command to release has been issued; and

updating the data structure to include the free blocks allocated to the file.

15. The method of claim 13, wherein the command is issued to a thinly provisioned disk.

16. The method of claim 15, wherein the thinly provisioned disk is a thinly provisioned virtual disk of a virtual machine, and the file is a file of the virtual machine.

17. A non-transitory computer readable storage medium comprising instructions executable in a computer system to cause the computer system to carry out a method for issuing a command to release free storage blocks previously allocated to a logical block device back to an underlying storage system supporting the logical block device, comprising:

identifying a set of free blocks to be released;

updating the set of free blocks to remove those free blocks that have already been released;

allocating the free blocks in the updated set to a file; and

issuing a command to release the free blocks allocated to the file.

18. The non-transitory computer readable storage medium of claim 17, wherein the method further comprises:

maintaining a data structure to track blocks for which the command to release has been issued; and

updating the data structure to include the free blocks allocated to the file.

19. The menon-transitory computer readable storage medium of claim 17, wherein the command is issued to a thinly provisioned disk.

20. The non-transitory computer readable storage medium of claim 19, wherein the thinly provisioned disk is a thinly provisioned virtual disk of a virtual machine, and the file is a file of the virtual machine.