Method and System for Providing Efficient Access to a Tape Storage System

• US 20110196829A1
• Filed: 02/08/2011
• Published: 08/11/2011
• Est. Priority Date: 02/09/2010
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Gheorghita, Stefan V., Zunger, Yonatan, Vickrey, Rebekah C., Dachille, Frank C.
• Granted Patent: US 8,874,523 B2
• Time in Patent Office: Days
• US Class Current: 707/622
• CPC Class Codes: G06F 16/275 Synchronous replication

Abstract

A method for asynchronously replicating data onto a tape medium is implemented at one or more server computers associated with a distributed storage system and connected to a tape storage system. Upon receiving a first request from a client for storing an object within the tape storage system, a server computer stores the object within a staging sub-system of the distributed storage system and provides a first response to the requesting client. If a predefined condition is met, the server computer transfers objects from the staging sub-system to the tape storage system. For each transferred object, the server computer adds a reference to the object to a tape management sub-system, identifies a corresponding parent object associated with the object and its metadata within a parent object management sub-system of the distributed storage system, and updates the parent object'"'"'s metadata to include the object'"'"'s location within the tape storage system.

Claims

1. A computer-implemented method for asynchronously replicating data onto a tape medium, comprising:

at a computing device having one or more processors and memory storing programs executed by the one or more processors, wherein the computing device is associated with a distributed storage system and connected to a tape storage system;

receiving a first request from a client for storing an object within the tape storage system;

storing the object within a staging sub-system of the distributed storage system, wherein the staging sub-system includes a plurality of objects scheduled to be transferred to the tape storage system;

providing a first response to the requesting client, the first response indicating that the first request has been performed synchronously;

transferring one or more objects from the staging sub-system to the tape storage system if a predefined condition is met; and

for a respective transferred object,

adding a reference to the object to a tape management sub-system of the tape storage system;

identifying a corresponding parent object associated with the object and its metadata within a parent object management sub-system of the distributed storage system; and

updating the parent object'"'"'s metadata to include the object'"'"'s location within the tape storage system.

2. The computer-implemented method of claim 1, wherein the first request identifies a source storage sub-system of the distributed storage system that has a replica of the object, further comprising:

upon receipt of the first request,

submitting a second request for the object to the source storage sub-system; and

receiving a second response from the source storage sub-system, wherein the second response includes the requested object.

3. The computer-implemented method of claim 1, further comprising:

before storing the object within the staging sub-system,

querying the tape management sub-system to determine whether there is a replica of the object within the tape storage system; and

adding a reference to the replica of the object to the tape management sub-system if there is a replica of the object within the tape storage system.

4. The computer-implemented method of claim 3, wherein the tape management sub-system of the distributed storage system includes a staging object index table and an external object index table, wherein an entry in the staging object index table identifies an object that has been scheduled to be transferred to the tape storage system and an entry in the external object index table identifies an object that has been transferred to the tape storage system.

5. The computer-implemented method of claim 4, wherein:

there is a replica of the object within the tape storage system if either of the staging and external object index tables includes an entry that corresponds to the object to be transferred to the tape storage system; and

there is no replica of the object within the tape storage system if neither of the staging and external object index tables includes an entry that corresponds to the object to be transferred to the tape storage system.

6. The computer-implemented method of claim 4, wherein storing the object within the staging sub-system further comprises:

adding to the staging object index table an entry that corresponds to the object.

7. The computer-implemented method of claim 4, wherein adding a reference to a respective newly-transferred object further comprises:

removing from the staging object index table an entry that corresponds to the newly-transferred object; and

adding to the external object index table an entry that corresponds to the newly-transferred object.

8. The computer-implemented method of claim 1, wherein the staging sub-system includes one or more batches of object transfer entries and an object data staging region, and storing the object within the staging sub-system further comprises:

storing the object to be transferred within the object data staging region;

identifying a respective batch in accordance with a locality hint provided with the first request, wherein the locality hint identifies a group of objects that are likely to be collectively restored from the tape storage system or expire from the tape storage system;

inserting an object transfer entry into the identified batch, the object transfer entry identifying a location of the object within the object data staging region; and

updating a total size of the identified batch in accordance with the newly-inserted object transfer entry and the object to be transferred.

9. The computer-implemented method of claim 8, wherein a respective object to be transferred includes content and metadata, and storing the object within the object data staging region further comprises:

writing the object'"'"'s content into a file in the object data staging region and the object'"'"'s metadata into a bigtable in the object data staging region.

10. The computer-implemented method of claim 1, wherein the first response is provided to the requesting client before the object is transferred to the tape storage system.

11. The computer-implemented method of claim 1, wherein the staging sub-system of the distributed storage system includes one or more batches of object transfer entries and an object data staging region, and transferring one or more objects from the staging sub-system to the tape storage system further comprises:

periodically scanning the one or more batches to determine their respective states;

identifying a respective batch of object transfer entries if a total size of the batch reaches a predefined threshold or the batch has been opened for at least a predefined time period;

closing the identified batch from accepting any more object transfer entry;

submitting an object transfer request to the tape storage system for the identified batch; and

for a respective object transfer entry within the identified batch,

retrieving the corresponding object from the object data staging region; and

transferring the object into the tape storage system.

12. The computer-implemented method of claim 11, further comprising:

deleting the identified batch from the staging sub-system after the last object transfer entry within the identified batch is processed.

13. The computer-implemented method of claim 11, wherein the closure of the identified batch triggers a creation of a new batch for incoming object transfer entries in the staging sub-system.

14. The computer-implemented method of claim 11, further comprising:

for a respective object transfer entry within the identified batch,

deleting the object transfer entry and the corresponding object from the identified batch and the object data staging region, respectively.

15. The computer-implemented method of claim 1, wherein updating the corresponding parent object'"'"'s metadata for a respective transferred object further comprise:

setting the parent object'"'"'s state as “

finalized”

if the object is the last object of the parent object to be transferred to the tape storage system; and

setting the parent object'"'"'s state as “

finalizing”

if the object is not the last object of the parent object to be transferred to the tape storage system.

16. A computer-implemented method for asynchronously replicating data from a tape medium, comprising:

at a computing device having one or more processors and memory storing programs executed by the one or more processors, wherein the computing device is associated with a distributed storage system and connected to a tape storage system;

receiving a first request from a client for restoring an object from the tape storage system to a destination storage sub-system of the distributed storage system;

generating an object restore entry that identifies the object to be restored and the destination storage sub-system;

storing the object restore entry within a staging sub-system of the distributed storage system, wherein the staging sub-system includes a plurality of object restore entries scheduled to be applied to the tape storage system;

providing a first response to the requesting client, indicating that the first request will be performed asynchronously;

applying one or more object restore entries within the staging sub-system to the tape storage system if a predefined condition is met; and

for a respective restored object,

transferring the object to the destination storage sub-system;

identifying a corresponding parent object associated with the object and its metadata within a parent object management sub-system of the distributed storage system; and

updating the parent object'"'"'s metadata to identify the object'"'"'s location within destination storage sub-system.

17. The computer-implemented method of claim 16, wherein the staging sub-system includes one or more batches of object restore entries and an object data staging region, and storing the object restore entry within the staging sub-system further comprises:

identifying a respective batch in accordance with a restore priority provided with the first request;

inserting the object restore entry into the identified batch; and

updating a total size of the identified batch in accordance with the newly-inserted object restore entry.

18. The computer-implemented method of claim 16, wherein the first response is provided to the requesting client before the object is restored from the tape storage system.

19. The computer-implemented method of claim 16, wherein the staging sub-system of the distributed storage system includes one or more batches of object restore entries, and applying one or more object restore entries to the tape storage system further comprises:

periodically scanning the one or more batches to determine their respective states;

identifying a respective batch of object restore entries if a total size of the batch reaches a predefined threshold or the batch has been opened for at least a predefined time period;

closing the identified batch from accepting any more object restore entry;

submitting an object restore request to the tape storage system for the closed batch; and

for a respective object restore entry within the identified batch,

retrieving the object from the tape storage system, the object including content and metadata; and

storing the object within an object data staging region of the staging sub-system, further comprising;

writing the object'"'"'s content into a file in the object data staging region and the object'"'"'s metadata into a bigtable in the object data staging region.

20. The computer-implemented method of claim 19, wherein the closure of the identified batch triggers a creation of a new batch for incoming object restore entries in the staging sub-system.

21. The computer-implemented method of claim 19, wherein transferring a respective restored object to the destination storage sub-system further comprises:

associating the destination storage sub-system in the object restore entry with the object in the object data staging region;

sending a request to an object management sub-system, the request identifying the destination storage sub-system and including a copy of the object in the object data staging region;

deleting the object restore entry and the corresponding object from the identified batch and the object data staging region, respectively.

22. The computer-implemented method of claim 16, wherein updating the corresponding parent object'"'"'s metadata for a respective restored object further comprise:

setting the parent object'"'"'s state as “

finalized”

if the object is the last object of the parent object to be restored from the tape storage system; and

setting the parent object'"'"'s state as “

finalizing”

if the object is not the last object of the parent object to be restored from the tape storage system.

23. A computing device associated with a distributed storage system, for asynchronously replicating data onto a tape medium, the computing device comprising:

one or more processors; and

memory storing one or more programs to be executed by the one or more processors;

the one or more programs comprising instructions for;

receiving a first request from a client for storing an object within the tape storage system;

storing the object within a staging sub-system of the distributed storage system, wherein the staging sub-system includes a plurality of objects scheduled to be transferred to the tape storage system;

providing a first response to the requesting client, the first response indicating that the first request has been performed synchronously;

transferring one or more objects from the staging sub-system to the tape storage system if a predefined condition is met; and

for a respective transferred object,

adding a reference to the object to a tape management sub-system of the tape storage system;

identifying a corresponding parent object associated with the object and its metadata within a parent object management sub-system of the distributed storage system; and

updating the parent object'"'"'s metadata to include the object'"'"'s location within the tape storage system.

24. A computing device associated with a distributed storage system, for asynchronously replicating data from a tape medium, the computing device comprising:

one or more processors; and

memory storing one or more programs to be executed by the one or more processors;

the one or more programs comprising instructions for;

receiving a first request from a client for restoring an object from the tape storage system to a destination storage sub-system of the distributed storage system;

generating an object restore entry that identifies the object to be restored and the destination storage sub-system;

storing the object restore entry within a staging sub-system of the distributed storage system, wherein the staging sub-system includes a plurality of object restore entries scheduled to be applied to the tape storage system;

providing a first response to the requesting client, indicating that the first request will be performed asynchronously;

applying one or more object restore entries within the staging sub-system to the tape storage system if a predefined condition is met; and

for a respective restored object,

transferring the object to the destination storage sub-system;

identifying a corresponding parent object associated with the object and its metadata within a parent object management sub-system of the distributed storage system; and

updating the parent object'"'"'s metadata to identify the object'"'"'s location within destination storage sub-system.

25. A non-transitory computer readable storage medium storing one or more programs configured for execution by a computing device associated with a distributed storage system, for asynchronously replicating data onto a tape medium, the one or more programs comprising instructions for:

receiving a first request from a client for storing an object within the tape storage system;

storing the object within a staging sub-system of the distributed storage system, wherein the staging sub-system includes a plurality of objects scheduled to be transferred to the tape storage system;

providing a first response to the requesting client, the first response indicating that the first request has been performed synchronously;

transferring one or more objects from the staging sub-system to the tape storage system if a predefined condition is met; and

for a respective transferred object,

adding a reference to the object to a tape management sub-system of the tape storage system;

identifying a corresponding parent object associated with the object and its metadata within a parent object management sub-system of the distributed storage system; and

updating the parent object'"'"'s metadata to include the object'"'"'s location within the tape storage system.

26. A non-transitory computer readable storage medium storing one or more programs configured for execution by a computing device associated with a distributed storage system, for asynchronously replicating data from a tape medium, the one or more programs comprising instructions for:

receiving a first request from a client for restoring an object from the tape storage system to a destination storage sub-system of the distributed storage system;

generating an object restore entry that identifies the object to be restored and the destination storage sub-system;

storing the object restore entry within a staging sub-system of the distributed storage system, wherein the staging sub-system includes a plurality of object restore entries scheduled to be applied to the tape storage system;

providing a first response to the requesting client, indicating that the first request will be performed asynchronously;

applying one or more object restore entries within the staging sub-system to the tape storage system if a predefined condition is met; and

for a respective restored object,

transferring the object to the destination storage sub-system;

identifying a corresponding parent object associated with the object and its metadata within a parent object management sub-system of the distributed storage system; and

updating the parent object'"'"'s metadata to identify the object'"'"'s location within destination storage sub-system.