System and method for reallocating blocks in checkpointing bitmap-based file systems

• US 8,370,301 B1
• Filed: 06/12/2007
• Issued: 02/05/2013
• Est. Priority Date: 03/21/2003
• Status: Active Grant

• Current Assignee: NetApp, Inc.
• Original Assignee: NetApp, Inc.
• Inventors: Chen, Raymond C.
• Primary Examiner(s): Saeed, Usmaan
• Application Number:
  US11/761,829
• Time in Patent Office: 2,065 Days
• Field of Search: None
• US Class Current: 707/640
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: G06F 16/10 File systems; File servers
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data
• CPC Class Codes: Y10S 707/99954 Version management

Abstract

A computerized file system has a first software layer for writing data blocks to persistent storage, and a second software layer for receiving requests from a client, and in response to receiving a request passing a command to the first software layer. A current bit map shows data blocks of persistent storage which are allocated to holding data of the file system. A safe copy of the current bit map is maintained. A third copy of the current bit map is passed, at a selected time, to the first software layer to enable the first software layer to write data blocks containing the bit map current at the selected time to the persistent storage, and simultaneously changing the current bit map as maintained in a computer memory while data blocks containing the bit map current at the selected time are written to the persistent storage.

Claims

1. A method for operating a storage system, comprising:

maintaining a first portion of a storage operating system of the storage system for writing data to persistent storage operatively connected to the storage system;

maintaining a second portion of the storage operating system for managing a plurality of bitmaps that track an allocation status of blocks of the persistent storage;

maintaining a first bitmap of the plurality of bitmaps;

maintaining a second bitmap comprising a first copy of the first bitmap;

determining that the first portion is to write the first bitmap to the persistent storage while the second portion is to modify at least one of the first bitmap and the second bitmap;

in response to determining that the first bitmap is to be written to the persistent storage while the second portion is to modify the at least one of the first bitmap and the second bitmap, creating a third bitmap comprising a second copy of the first bitmap;

in response to creating the third bitmap, using the third bitmap by the first portion to be written to the persistent storage, and using the at least one of the first bitmap and the second bitmap by the second portion for modifications;

executing a block allocation procedure to allocate a data block to the persistent storage;

marking the data block as allocated in the first bitmap and the second bitmap; and

waiting until the first portion finishes writing the data block to the persistent storage, and in response to finishing, discarding the third bitmap.

2. The method as in claim 1, further comprising:

finishing writing the third bitmap to the persistent storage, and in response, discarding the third bitmap.

3. The method as in claim 1, further comprising:

using a redundant array of independent disk (RAID) portion as the first portion.

4. The method as in claim 1, further comprising:

using an active map as the first bitmap.

5. The method as in claim 1, further comprising:

determining whether the second bitmap exists, and in response to determining the second bitmap does not exist, creating the second bitmap.

6. The method as in claim 1, further comprising:

using a file system portion as the second portion.

7. The method as in claim 1, further comprising:

waiting until the third bitmap is written to the persistent storage; and

in response to the third bitmap being written to the persistent storage, discarding the second bitmap.

8. The method as in claim 1, further comprising:

determining whether a first data block associated with the first bitmap is allocated in a snapshot;

determining whether the first data block is free in the second bitmap; and

allocating the first data block in response to determining the first data block is not allocated in the snapshot and in response to determining the first data block is free in the second bitmap.

9. The method as in claim 1, further comprising:

modifying memory pointers to create the second bitmap by having the memory pointers point to the first bitmap.

10. A computerized storage system, comprising:

a first portion of a storage operating system of the storage system configured to write data to persistent storage operatively connected to the computerized storage system;

a second portion of the storage operating system configured to manage a plurality of bitmaps that track an allocation status of blocks of the persistent storage;

the second portion further configured to maintain a first bitmap of the plurality of bitmaps to show data allocation of the persistent storage;

the second portion further configured to maintain a second bitmap comprising a first copy of the first bitmap;

the second portion further configured to maintain a third bitmap comprising a second copy of the first bitmap;

the first portion further configured to write the third bitmap to the persistent storage while a modification to at least one of the first bitmap and the second bit map is to occur;

the second portion further configured to use the at least one of the first bitmap and the second bitmap for modifications, wherein the first portion is further configured to write the third bitmap to the persistent storage;

a processor configured to;

execute block allocation procedure to allocate a data block to the persistent storage;

mark the data block as allocated in the first bitmap and the second bitmap; and

wait until the first portion finishes writing the data block to the persistent storage, and in response to finishing, discard the third bitmap.

11. The computerized storage system of claim 10, further comprising:

the first portion further configured to discard the third bitmap in response to finishing writing the third bitmap to the persistent storage.

12. The computerized storage system of claim 10, further comprising:

wherein the first portion comprises a redundant array of independent disks (RAID) portion.

13. The computerized storage system of claim 12, further comprising:

wherein the first bitmap comprises an active map.

14. The computerized storage system of claim 10, further comprising:

wherein the second bitmap is created in response to the second portion determining the second bitmap does not exist.

15. The computerized storage system of claim 10, further comprising:

wherein the second portion comprises a file system portion.

16. The computerized storage system of claim 10, further comprising:

a process configured to determine whether a first data block associated with the first bitmap is allocated in a snapshot;

the process further configured to determine whether the first data block is free in the second bitmap; and

the process further configured to allocate the block in response to determining the first data block is not allocated in the snapshot and in response to determining the first data block is free in the second bitmap.

17. The computerized storage system of claim 10, further comprising:

a memory configured to store the second bitmap, wherein the second portion is further configured to modify pointers in the memory to point to the first bitmap to create the second bitmap.

18. A non-transitory computer readable media containing executable program instructions executed by a processor, comprising:

program instructions that maintain a first portion of a storage operating system of a storage system for writing data to persistent storage operatively connected to the storage system;

program instructions that maintain a second portion of the storage operating system for managing a plurality of bitmaps that track an allocation status of blocks of the persistent storage;

program instructions that maintain a first bitmap of the plurality of bitmaps;

program instructions that maintain a second bitmap comprising a first copy of the first bitmap;

program instructions that determine that the first portion is to write the first bitmap to the persistent storage while the second portion is to modify at least one of the first bitmap and the second bitmap;

program instructions that, in response to determining that the first bitmap is to be written to the persistent storage while the second portion is to modify the at least one of the first bitmap and the second bitmap, create a third bitmap comprising a second copy of the first bitmap;

program instructions that, in response to creating the third bitmap, use the third bitmap by the first portion to be written to the persistent storage, and program instructions that use the at least one of the first bitmap and the second bitmap by the second portion for modifications;

program instructions that execute a block allocation procedure to allocate a data block to the persistent storage;

program instructions that mark the data block as allocated in the first bitmap and the second bitmap; and

program instructions that wait until the first portion finishes writing the data block to the persistent storage, and in response to finishing, discarding the third bitmap.