FILE SYSTEM DRIVEN RAID REBUILD TECHNIQUE

• US 20150205669A1
• Filed: 01/22/2014
• Published: 07/23/2015
• Est. Priority Date: 01/17/2014
• Status: Active Grant

• Current Assignee: NetApp, Inc.
• Original Assignee: NetApp, Inc.
• Inventors: Sundaram, Rajesh, Baddepudi, Bharat, Kimmel, Jeffrey S., Rakitzis, T. Byron
• Granted Patent: US 9,389,958 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1008 in individual solid state devices G06F11/1004 takes precedence
• CPC Class Codes: G06F 11/1068 in sector programmable memories, e.g. flash disk G06F11/1072 takes precedence
• CPC Class Codes: G06F 11/1076 Parity data used in redundant arrays of independent storages, e.g. in RAID systems
• CPC Class Codes: G06F 11/108 Parity data distribution in semiconductor storages, e.g. in SSD
• CPC Class Codes: G06F 11/1084 Degraded mode, e.g. caused by single or multiple storage removals or disk failures
• CPC Class Codes: G06F 11/1092 Rebuilding, e.g. when physically replacing a failing disk
• CPC Class Codes: G06F 11/1096 Parity calculation or recalculation after configuration or reconfiguration of the system
• CPC Class Codes: G06F 16/1847 specifically adapted to static storage, e.g. adapted to flash memory or SSD
• CPC Class Codes: G06F 2211/1057 Parity-multiple bits-RAID6, i.e. RAID 6 implementations
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/0653 Monitoring storage devices or systems
• CPC Class Codes: G06F 3/0688 Non-volatile semiconductor memory arrays
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD
• CPC Class Codes: G11C 29/52 Protection of memory contents; Detection of errors in memory contents

Abstract

In one embodiment, a file system driven RAID rebuild technique is provided. A layered file system may organize storage of data as segments spanning one or more sets of storage devices, such as solid state drives (SSDs), of a storage array, wherein each set of SSDs may form a RAID group configured to provide data redundancy for a segment. The file system may then drive (i.e., initiate) rebuild of a RAID configuration of the SSDs on a segment-by-segment basis in response to cleaning of the segment (i.e., segment cleaning). Each segment may include one or more RAID stripes that provide a level of data redundancy (e.g., single parity RAID 5 or double parity RAID 6) as well as RAID organization (i.e., distribution of data and parity) for the segment. Notably, the level of data redundancy and RAID organization may differ among the segments of the array.

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 connected to a storage array of solid state drives (SSDs) forming a storage pool;

organizing a first set of the SSDs into a first redundancy group having a first redundancy configuration;

storing the data in a first segment associated with the first redundancy group, wherein the first segment has a log-structured layout, wherein the first segment spans the first redundancy group;

in response to a failed SSD in the first redundancy group, allocating a second segment associated with a second redundancy group, wherein the second segment has a log-structured layout, wherein the second redundancy group is organized from the first set of SSDs excluding the failed SSD, wherein the second segment spans the second redundancy group, wherein the second redundancy group has a second redundancy configuration; and

rebuilding redundancy in response to cleaning the first segment, the cleaning to copy valid blocks of the data from the first segment to the second segment according to the second redundancy configuration, while omitting any deleted or overwritten blocks of the data.

2. The method of claim 1 wherein the first segment comprises a plurality of stripes according to the first redundancy configuration spanning the first redundancy group.

3. The method of claim 1 wherein the first redundancy configuration is different than the second redundancy configuration.

4. The method of claim 2 wherein a first parity distribution of the first redundancy group differs from a second parity distribution of the second redundancy group, and wherein the first parity distribution has a fixed arrangement among the plurality of stripes of the first segment.

5. The method of claim 1 wherein the first redundancy group has a same number of parity SSDs as the second redundancy group.

6. The method of claim 1 wherein the cleaning is initiated in response to an amount of free space of the storage pool being less than a free space threshold.

7. The method of claim 1 further comprising:

in response to removing an SSD from the storage array of SSDs, allocating a third segment associated with a third redundancy group, wherein the third segment has a log-structured layout, wherein the third redundancy group is organized from the first set of SSDs including a new SSD and excluding the failed SSD, wherein the third segment spans the third redundancy group, wherein the third redundancy group has a third redundancy configuration; and

cleaning the first segment by copying the data from the first segment to the third segment according to the third redundancy configuration.

8. The method of claim 1 wherein the failed SSD returns on-line.

9. The method of claim 1 where in the SSDs include flash components.

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 connected to a storage array of solid state drives (SSDs);

organizing a first set of the SSDs into a first redundancy group having a first redundancy configuration;

storing the data in a first segment associated with the first redundancy group, wherein the first segment has a log-structured layout, wherein the first segment includes a plurality of stripes according to the first redundancy configuration spanning the first redundancy group, wherein the first plurality of stripes includes a first fixed parity arrangement; and

cleaning the first segment by copying the data from the first segment to a second segment associated with a second redundancy group, wherein the second segment has a log-structured layout, wherein the second segment includes a plurality of stripes according to the first redundancy configuration spanning the second redundancy group, wherein the second plurality of stripes includes a second fixed parity arrangement where parity is stored on one or more different SSDs than the first fixed parity arrangement.

11. A system comprising:

a storage system having a memory connected to a processor via a bus;

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

a storage I/O stack executing on the processor of the storage system, the storage I/O stack when executed operable to;

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

organize a first set of SSDs into a first redundancy group having a first redundancy configuration;

store the data in a first segment associated with the first redundancy group, wherein the first segment has a log-structured layout, wherein the first segment spans the first redundancy group;

in response to a failed SSD in the first redundancy group, allocate a second segment associated with a second redundancy group, wherein the second segment has a log-structured layout, wherein the second redundancy group is organized from the first set of SSDs excluding the failed SSD, wherein the second segment spans the second redundancy group, wherein the second redundancy group has a second redundancy configuration; and

rebuild redundancy in response to cleaning the first segment, the cleaning to copy valid blocks of the data from the first segment to the second segment according to the second redundancy configuration, while omitting any deleted or overwritten blocks of the data, wherein the second segment includes a set of chunks, each chunk stored on an SSD of the second redundancy group, wherein a first chunk is written as a contiguous range with temporal locality.

12. The system of claim 11 wherein the first segment comprises a plurality of stripes according to the first redundancy configuration spanning the first redundancy group.

13. The system of claim 12 wherein a first parity distribution of the first redundancy group differs from a second parity distribution of the second redundancy group, and wherein the first parity distribution has a fixed arrangement among the plurality of stripes of the first segment.

14. The system of claim 11 wherein the first redundancy configuration is different than the second redundancy configuration.

15. The system of claim 11 wherein the first redundancy group has a same number of parity SSDs as the second redundancy group.

16. The system of claim 11 wherein operation of the storage I/O stack to clean is initiated in response to an amount of free space of the storage pool being less than a free space threshold.

17. The system of claim 11 wherein the storage I/O stack when executed is further operable to:

in response to a new SSD added to the storage pool, allocate a third segment associated with a third redundancy group, wherein the third segment has a log-structured layout, wherein the third redundancy group is organized from the first set of SSDs including the new SSD and excluding the failed SSD, wherein the third segment spans the third redundancy group, wherein the third redundancy group has a third redundancy configuration; and

clean the first segment by copying the data from the first segment to the third segment according to the third redundancy configuration.

18. The system of claim 11 wherein the failed SSD returns on-line while the first segment is being cleaned.

19. The system of claim 11 wherein the SSDs include flash components.

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

in response to the failed SSD recovering, allocate a third segment associated with a third redundancy group, wherein the third segment has a log-s structured layout, wherein the third redundancy group is organized from the first set of SSDs including the recovered SSD, wherein the third segment spans the third redundancy group, wherein the third redundancy group has a third redundancy configuration; and

clean the first segment by copying the data from the first segment to the third segment according to the third redundancy configuration.