Method and system for path selection in a network

• US 8,619,555 B2
• Filed: 11/17/2010
• Issued: 12/31/2013
• Est. Priority Date: 11/17/2010
• Status: Active Grant

• Current Assignee: NetApp, Inc.
• Original Assignee: NetApp, Inc.
• Inventors: Dallas, William D., Busick, Chris
• Primary Examiner(s): Hsu, Alpus H
• Assistant Examiner(s): PATEL, DHARMESH J
• Application Number:
  US12/948,498
• Publication Number:
  US 20120124414A1
• Time in Patent Office: 1,140 Days
• Field of Search: 709/239, 709/241, 370/238, 370/244, 370/248, 370/395.32, 710/29, 710/38, 714/2, 714/48
• US Class Current: 370/228
• CPC Class Codes: G06F 11/2005 using redundant communication controllers
• CPC Class Codes: G06F 11/2007 using redundant communication media
• CPC Class Codes: H04L 41/069 using logs of notifications; Post-processing of notifications
• CPC Class Codes: H04L 45/12 Shortest path evaluation
• CPC Class Codes: H04L 45/22 Alternate routing
• CPC Class Codes: H04L 45/28 using route fault recovery
• CPC Class Codes: H04L 67/1097 for distributed storage of data in networks, e.g. transport arrangements for network file system [NFS], storage area networks [SAN] or network attached storage [NAS]

Abstract

Method and system for handling error events on a current path for processing an I/O request for reading information from and writing information to a storage space is provided. A system is able to communicate with the storage space via more than one path. If the current path reports an error event, then an alternate path quality is determined to ascertain whether the alternate path will generate an error similar to the current path. The alternate path quality is determined based on a plurality of factors which are assigned certain weights. The weights are determined based on a likely contribution of each factor to a repetition of the error reported by the current path. If the alternate path quality is equal to or exceeds a programmable threshold value, then the alternate path is selected.

Claims

1. A machine implemented method for transmitting an input/output (“

I/O”

) request between a storage system and a storage array, comprising;

assigning a weight to a plurality of factors for determining a path quality of a plurality of paths between the storage system and the storage array;

wherein a value of each weight is based on a likely contribution of each factor to a repetition of an error reported by a current path that is being used for transmitting the I/O request; and

wherein the path quality provides a likelihood of reporting an error on an alternate path similar to the error reported on the current path;

assigning a threshold value for a path quality of each alternate path available to transmit the I/O request, when the current path reports an error;

wherein the threshold value is a minimum path quality for selecting a path for transmitting the I/O request without having to evaluate other available alternate paths;

determining if an alternate path is available for transmitting the I/O request, after an error is reported by the current path;

determining a path quality of the alternate path based on the weights assigned to the plurality of factors; and

selecting the alternate path when the path quality of the alternate path is at least equal to the threshold value.

2. The method of claim 1, further comprising:

determining a path quality of other alternate paths available for transmitting the I/O request, if the path quality of the alternate path is less than the threshold value; and

selecting an alternate path from among the other alternate paths with a highest path quality.

3. The method of claim 2, wherein the path quality of the other alternate paths is stored in a data structure.

4. The method of claim 1, wherein a factor from among the plurality of factors is based on an error rate reported by the alternate path.

5. The method of claim 4, wherein a weight for the factor is higher if a lower error rate is reported by the alternate path.

6. The method of claim 1, wherein a factor from among the plurality of factors is based on whether a same target port group is used by the current path and the alternate path.

7. The method of claim 6, wherein a weight for the factor is higher if the same target port group is not used by the current path and the alternate path.

8. The method of claim 1, wherein a factor from among the plurality of factors is based on whether a same target port is used by the current path and the alternate path.

9. The method of claim 8, wherein a weight for the factor is higher if the same target port is not used by the current path and the alternate path.

10. The method of claim 1, wherein a factor from among the plurality of factors is based on whether a same switch is used by the current path and the alternate path.

11. The method of claim 10, wherein a weight for the factor is higher if the same switch is not used by the current path and the alternate path.

12. The method of claim 1, wherein a factor from among the plurality of factors is based on whether a same adapter is used by the current path and the alternate path.

13. The method of claim 12, wherein a weight for the factor is higher if the same adapter is not used by the current path and the alternate path.

14. A machine implemented method for transmitting an input/output (“

I/O”

) request between a storage system and a storage array, comprising;

determining that an alternate path is available for transmitting the I/O request when an error is reported by a current path that is being used for transmitting the I/O request;

determining a path quality of the alternate path;

wherein the path quality is based on a weight assigned to a plurality of factors associated with a plurality of components between the storage system and the storage array and a value of each weight is based on a likely contribution of each factor to a repetition of the error reported by the current path;

selecting the alternate path when the path quality is at least equal to a threshold value;

wherein the threshold value is a minimum path quality used for selecting the alternate path for transmitting the I/O request without having to evaluate other available alternate paths;

determining a path quality of other available alternate paths, when the path quality of the alternate path is less than the threshold value; and

selecting an alternate path from among the other alternate paths with a highest path quality.

15. The method of claim 14, wherein a factor from among the plurality of factors is based on an error rate reported by the alternate path.

16. The method of claim 15, wherein a weight for the factor is higher if a lower error rate is reported by the alternate path.

17. The method of claim 14, wherein a factor from among the plurality of factors is based on whether a same target port group is used by the current path and the alternate path.

18. The method of claim 17, wherein a weight for the factor is higher if the same target port group is not used by the current path and the alternate path.

19. The method of claim 14, wherein a factor from among the plurality of factors is based on whether a same target port is used by the current path and the alternate path.

20. The method of claim 19, wherein a weight for the factor is higher if the same target port is not used by the current path and the alternate path.

21. The method of claim 14, wherein a factor from among the plurality of factors is based on whether a same switch is used by the current path and the alternate path.

22. The method of claim 21, wherein a weight for the factor is higher if the same switch is not used by the current path and the alternate path.

23. The method of claim 14, wherein a factor from among the plurality of factors is based on whether a same adapter is used by the current path and the alternate path.

24. The method of claim 23, wherein a weight for the factor is higher if the same adapter is not used by the current path and the alternate path.

25. A system, comprising:

a storage system and a storage array using a current path having a plurality of components for processing an input/output (“

I/O”

) request; and

a processor for the storage system executing instructions for determining that an alternate path is available for transmitting the I/O request, after an error is reported by the current path; and

determining a path quality of the alternate path;

wherein the path quality is based on a weight assigned to a plurality of factors associated with the plurality of components between the storage system and the storage array and a value of each weight is based on a likely contribution of each factor to a repetition of the error reported by the current path; and

wherein the alternate path is selected when the path quality is at least equal to a threshold value, which is a minimum path quality for selecting the alternate path for transmitting the I/O request without having to evaluate other available paths.

26. The system of claim 25, wherein a path quality of other alternate paths available for transmitting the I/O request is determined, if the path quality of the alternate path is less than the threshold value;

and an alternate path from among the other alternate paths with a highest path quality is selected.

27. The system of claim 25, wherein a factor from among the plurality of factors is based on an error rate reported by the alternate path.

28. The system of claim 27, wherein a weight for the factor is high if a lower rate is reported by the alternate path.

29. The system of claim 25, wherein a factor from among the plurality of factors is based on whether a same target port group is used by the current path and the alternate path.

30. The system of claim 29, wherein a weight for the factor is higher if the same target port group is not used by the current path and the alternate path.

31. The system of claim 25, wherein a factor from among the plurality of factors is based on whether a same target port is used by the current path and the alternate path.

32. The system of claim 31, wherein a weight for the factor is higher if the same target port is not used by the current path and the alternate path.

33. The system of claim 25, wherein a factor from among the plurality of factors is based on whether a same switch is used by the current path and the alternate path.

34. The system of claim 33, wherein a weight for the factor is higher if the same switch is not used by the current path and the alternate path.

35. The system of claim 25, wherein a factor from among the plurality of factors is based on whether a same adapter is used by the current path and the alternate path.

36. The system of claim 35, wherein a weight for the factor is higher if the same adapter is not used by the current path and the alternate path.

37. A machine implemented method, comprising:

generating a data structure comprising a weight assigned to a factor for determining a path quality of a path between a processor executable system and a storage space;

detecting an error associated with transmitting an input/output (I/O) request through a first path; and

accessing the data structure to determine an alternate path for transmitting the I/O request based on the weight assigned to the factor;

wherein a value of the weight is based on a likely contribution of the factor to a repetition of the error reported by the first path and the alternate path is selected when the path quality of the alternate path is at least equal to a threshold value which is an indicator of an acceptable path quality for the alternate path;

wherein the alternate path is selected if the path quality is equal to a threshold value, which is a minimum path quality for selecting an alternate path for transmitting the I/O request without having to evaluate other available paths.

38. The method of claim 37, wherein a path quality of the other available paths is determined, if the path quality of the alternate path is less than the threshold value;

and an alternate path from among the other available paths with a highest path quality is selected.