Optimized segment cleaning technique

• US 10,133,511 B2
• Filed: 09/12/2014
• Issued: 11/20/2018
• Est. Priority Date: 09/12/2014
• Status: Active Grant

• Current Assignee: NetApp, Inc.
• Original Assignee: NetApp, Inc.
• Inventors: Muth, John, McClanahan, Edward D., Patel, Dhaval, Swaminathan, Manish
• Primary Examiner(s): Rossiter, Sean D
• Assistant Examiner(s): Choi, Charles J
• Application Number:
  US14/484,820
• Publication Number:
  US 20160077746A1
• Time in Patent Office: 1,530 Days
• Field of Search: 711159
• CPC Class Codes: G06F 2212/7205 Cleaning, compaction, garbage collection, erase control
• CPC Class Codes: G06F 3/0608 Saving storage space on storage systems
• CPC Class Codes: G06F 3/061 Improving I/O performance
• CPC Class Codes: G06F 3/0644 Management of space entities, e.g. partitions, extents, pools
• CPC Class Codes: G06F 3/0652 Erasing, e.g. deleting, data cleaning, moving of data to a wastebasket
• CPC Class Codes: G06F 3/0673 Single storage device
• CPC Class Codes: G06F 3/0688 Non-volatile semiconductor memory arrays

Abstract

An optimized segment cleaning technique is configured to efficiently clean one or more selected portions or segments of a storage array coupled to one or more nodes of a cluster. A bottom-up approach of the segment cleaning technique is configured to read all blocks of a segment to be cleaned (i.e., an “old” segment) to locate extents stored on the SSDs of the old segment and examine extent metadata to determine whether the extents are valid and, if so, relocate the valid extents to a segment being written (i.e., a “new” segment). A top-down approach of the segment cleaning technique obviates reading of the blocks of the old segment to locate the extents and, instead, examines the extent metadata to determine the valid extents of the old segment. A hybrid approach may extend the top-down approach to include only full stripe read operations needed for relocation and reconstruction of blocks as well as retrieval of valid extents from the stripes, while also avoiding any unnecessary read operations of the bottom-down approach.

Claims

1. A method comprising:

receiving a write request directed towards a logical unit (LUN), the write request having data and processed at a node of a cluster, the node having a processor, a memory and connected to a storage array of solid state drives (SSDs);

generating a first key from the data;

storing the data as a first extent in a first segment according to a log-structured layout, the first segment spanning a set of the SSDs, the first segment associated with a first segment identifier (ID), the first extent including the first key;

using an in-core metadata table to determine whether the first extent is valid when the first segment is above a capacity threshold;

reading the first extent from the first segment to determine whether the first extent is valid when the first segment is below the capacity threshold;

in response to determining that the first extent is valid, cleaning the first segment by copying the first extent from the first segment to a second segment, the second segment having the log-structured layout and associated with a second segment ID different than the first segment ID; and

updating an entry of the in-core metadata table to include the second segment ID, the entry including the first key.

2. The method of claim 1 wherein cleaning the first segment further comprises:

copying the first extent from a first location of the first segment to a second location of the second segment.

3. The method of claim 2 further comprising:

in response to determining that the first extent is valid, updating the entry to include the second location.

4. The method of claim 1 further comprising:

finding the entry of the in-core metadata table using the first key; and

using the entry to determine whether the first extent is valid.

5. The method of claim 1 further comprising:

examining metadata of the first extent read from the first segment;

finding the entry of the in-core metadata table using the first key of the first extent, the entry having an entry segment ID;

matching the entry segment ID to the first segment ID of the first segment; and

in response to matching the entry segment ID to first segment ID of the first segment, copying the first extent to the second segment.

6. The method of claim 1 further comprising:

scanning the in-core metadata table using the first segment ID to find the entry, the entry having the first segment ID and the first key;

copying the first extent from a first location of the first segment to a second location of the second segment; and

updating the entry to include the second location.

7. The method of claim 1 wherein a first approach to segment cleaning is used when a SSD of the set of the SSDs is inaccessible, wherein a second approach to segment cleaning is used when the first segment is below the capacity threshold, wherein the first approach to segment cleaning reads all extents included in the first segment, and wherein the second approach to segment cleaning reads only valid extents included in the first segment.

8. The method of claim 1 further comprising:

reading a block of the first segment as a stripe read operation spanning the set of the SSDs of the first segment, wherein the first extent and a second extent are included in the block of the first segment, wherein the first extent is compressed, and wherein a first location of the first extent equals a second location of the second extent.

9. The method of claim 1 further comprising:

coalescing reading of a first location of the first extent with a second location of a second extent, wherein the first extent and the second extent are included in a block of the first segment.

10. A method comprising:

receiving a write request directed towards a logical unit (LUN), the write request having data and processed at a node of a cluster, the node having a memory and connected to a storage array of solid state drives (SSDs);

associating the data with a first key;

storing the data as a first extent in a first segment according to a log-structured layout, the first segment spanning a set of the SSDs, the first segment associated with a first segment identifier (ID), the first extent including the first key;

scanning an in-core metadata table using the first segment ID to find an entry to determine whether the first extent is valid when the first segment is above a capacity threshold, the entry having the first segment ID and the first key;

reading the first extent from the first segment to determine whether the first extent is valid when the first segment is below the capacity threshold;

in response to determining that the first extent is valid, copying the first extent from the first segment to a location on a second segment, the second segment having the log-structured layout and associated with a second segment ID different than the first segment ID; and

updating the entry of the in-core metadata table to include the second segment ID and the location.

11. A system comprising:

a storage system having a memory connected to a processor;

a storage array coupled to the storage system having one or more solid state drives (SSDs);

a storage I/O stack executing on the processor of the storage system, the storage I/O stack configured to;

receive a write request directed towards a logical unit (LUN), the write request having data;

generate a first key from the data;

store the data as a first extent in a first segment according to a log-structured layout, the first segment spanning a set of the SSDs, the first segment associated with a first segment identifier (ID), the first extent including the first key;

use an in-core metadata table to determine whether the first extent is valid when the first segment is above a capacity threshold;

read the first extent from the first segment to determine whether the first extent is valid when the first segment is below the capacity threshold;

in response to determining that the first extent is valid, clean the first segment by copying the first extent from the first segment to a second segment, the second segment having the log-structured layout and associated with a second segment ID different than the first segment ID; and

update an entry of the in-core metadata table to include the second segment ID, the entry including the first key.

12. The system of claim 11 wherein the storage I/O stack configured to clean the first segment is further configured to:

copy the first extent from a first location to a second location.

13. The system of claim 11 wherein the storage I/O stack is further configured to:

find the entry of the in-core metadata table using the first key; and

use the entry to determine whether the first extent is valid.

14. The system of claim 12 wherein the storage I/O stack is further configured to:

in response to determining that the first extent is valid, update the entry to include the second location.

15. The system of claim 11 wherein the storage I/O stack is further configured to:

examine metadata of the first extent read from the first segment;

find the entry of the in-core metadata table using the first key of the first extent, the entry having an entry segment ID;

match the entry segment ID to the first segment ID of the first segment; and

in response to matching the entry segment ID to the first segment ID of the first segment, copy the first extent to the second segment.

16. The system of claim 11 wherein the storage I/O stack is further configured to:

scan the in-core metadata table using the first segment ID to find the entry, the entry having the first segment ID and the first key;

copy the first extent from a first location to a second location; and

update the entry to include the second location.

17. The system of claim 11 wherein a first approach to segment cleaning is used when a SSD of the set of the SSDs is inaccessible, wherein a second approach to segment cleaning is used when the first segment is below the capacity threshold, wherein the first approach to segment cleaning reads all extents included in the first segment, and wherein the second approach to segment cleaning reads only valid extents included in the first segment.

18. The system of claim 11 wherein the storage I/O stack is further configured to:

read a block of the first segment as a full stripe read operation spanning the set of the SSDs of the first segment, wherein the first extent and a second extent are included in the block of the first segment, wherein the first extent is compressed, and wherein a first location of the first extent equals a second location of the second extent.

19. The system of claim 18 wherein the full stripe read operation occurs in response to a failed SSD of the set of the SSDs of the first segment.

20. The system of claim 11 wherein the storage I/O stack is further configured to:

coalesce reading of a first location of the first extent with a second location of a second extent, wherein the first extent and the second extent are included in a block of the first segment.