System and method for verifying consistent points in file systems

1. A computer-implemented method for maintaining a consistent point of a file system, the method comprising: receiving a request to verify a first prime representing a first consistent point of a file system of a storage system having a plurality of storage units, wherein the first prime is collectively represented by a plurality of prime segments, each of the plurality of prime segments representing a token marking a head of a log file in the file system, wherein the verifying includes determining whether each of the plurality of prime segments exists in one of the plurality of storage units;

in response to receiving the request, examining, by an archiver executed by a processor, each of the plurality of prime segments collectively representing the first prime to determine whether the corresponding prime segment has been previously verified via a second prime representing a last known installable prime, including, for each of the plurality of prime segments collectively representing the first prime, determining whether the prime segment is included in a plurality of prime segments collectively representing the second prime, wherein each of the prime segments is stored in one of the storage units, respectively, wherein the first consistent point of the file system was captured at a first given point in time, wherein the second prime represents a second consistent point of the file system that was captured at a second given point in time prior to the first given point in time; and

determining, by the archiver, at least a first of the prime segments that has not been previously verified, without verifying a second of the prime segments that has been previously verified, wherein verifying the first of the prime segments and the second of the prime segments includes determining whether the first and the second of the prime segments exist in their respective storage units, wherein the first prime, when at least the first prime segment has been successfully verified, can be used to construct the first consistent point of the file system for a purpose of restoring the file system to a known consistent point, wherein the plurality of storage units include a first storage unit and a second storage unit, wherein the first storage unit is an active storage unit and the second storage unit is an archive storage unit that archives data of the first storage unit, and wherein the first prime segment is only stored in the first storage unit and the second prime segment is only stored in the second storage unit, wherein the second prime was recorded as an installable prime in a persistent storage location of the storage system, wherein each of a plurality of prime segments collectively representing the second prime has been verified, wherein a prime segment included in the plurality of prime segments collectively representing the second prime is not to be verified again for a purpose of verifying the first prime.

2. The method of claim 1 , wherein each of the storage units is configured to store segments of data files that are deduplicated within the corresponding storage unit.

3. The method of claim 2 , wherein each of the first and second primes is represented by a prime dependency list having a plurality of entries which represent the plurality of prime segments collectively representing each of the first and second primes.

4. The method of claim 3 , wherein each of the entries in the prime dependency list comprises a prime segment identifier (ID) associated with a storage unit ID indicating that a prime segment identified by the prime segment ID is supposed to be stored in one of the storage units identified by the storage unit ID.

5. The method of claim 4 , wherein determining whether a prime segment has been previously verified further comprises matching the prime segment ID and the storage unit ID in each entry between dependency lists of the first and second primes.

6. A non-transitory computer-readable storage medium having instructions stored therein, which when executed by a computer, cause the computer to perform operations of maintaining a consistent point of a file system, the operations comprising:

receiving a request to verify a first prime representing a first consistent point of a file system of a storage system having a plurality of storage units, wherein the first prime is collectively represented by a plurality of prime segments, each of the plurality of prime segments representing a token marking a head of a log file in the file system, wherein the verifying includes determining whether each of the plurality of prime segments exists in one of the plurality of storage units;

in response to receiving the request, examining, by an archiver executed by a processor, each of the plurality of prime segments collectively representing the first prime to determine whether the corresponding prime segment has been previously verified via a second prime representing a last known installable prime, including, for each of the plurality of prime segments collectively representing the first prime, determining whether the prime segment is included in a plurality of prime segments collectively representing the second prime, wherein each of the prime segments is stored in one of the storage units, respectively, wherein the first consistent point of the file system was captured at a first given point in time, wherein the second prime represents a second consistent point of the file system that was captured at a second given point in time prior to the first given point in time; and

determining, by the archiver, at least a first of the prime segments that has not been previously verified, without verifying a second of the prime segments that has been previously verified, wherein verifying the first of the prime segments and the second of the prime segments includes determining whether the first and the second of the prime segments exist in their respective storage units, wherein the first prime, when at least the first prime segment has been successfully verified, can be used to construct the first consistent point of the file system for a purpose of restoring the file system to a known consistent point, wherein the plurality of storage units include a first storage unit and a second storage unit, wherein the first storage unit is an active storage unit and the second storage unit is an archive storage unit that archives data of the first storage unit, and wherein the first prime segment is only stored in the first storage unit and the second prime segment is only stored in the second storage unit, wherein the second prime was recorded as an installable prime in a persistent storage location of the storage system, the second prime being collectively represented by a plurality of prime segments of which each of the prime segments has been verified, wherein a prime segment included in the plurality of prime segments collectively representing the second prime is not to be verified again for a purpose of verifying the first prime.

7. The non-transitory computer-readable storage medium of claim 6 , wherein each of the storage units is configured to store segments of data files that are deduplicated within the corresponding storage unit.

8. The non-transitory computer-readable storage medium of claim 7 , wherein each of the first and second primes is represented by a prime dependency list having a plurality of entries which represent the plurality of prime segments collectively representing each of the first and second primes.

9. The non-transitory computer-readable storage medium of claim 8 , wherein each of the entries in the prime dependency list comprises a prime segment identifier (ID) associated with a storage unit ID indicating that a prime segment identified by the prime set ID is supposed to be stored in one of the storage units identified by the storage unit ID.

10. The non-transitory computer-readable storage medium of claim 9 , wherein determining whether a prime segment has been previously verified further comprises matching the prime segment ID and the storage unit ID in each entry between dependency lists of the first and second primes.

11. A storage system, comprising:

a plurality of storage units, each storage unit storing segments of data files that are deduplicated within the respective storage unit, wherein the plurality of storage units include a first storage unit and a second storage unit, wherein the first storage unit is an active storage unit and the second storage unit is an archive storage unit that archives data of the first storage unit;

an archiver coupled to the storage units configured to

receive a request to verify a first prime representing a first consistent point of a file system, wherein the first prime is collectively represented by a plurality of prime segments, each of the plurality of prime segments representing a token marking a head of a log file in the file system, wherein the verifying includes determining whether each of the plurality of prime segments exists in one of the plurality of storage units,

in response to receiving the request, examine each of the plurality of prime segments collectively representing the first prime to determine whether the corresponding prime segment has been previously verified via a second prime representing a last known installable prime, including, for each of the plurality of prime segments collectively representing the first prime, the archiver is configured to determine whether the prime segment is included in the plurality of prime segments collectively representing the second prime, wherein each of the prime segments is stored in one of the storage units, respectively, wherein the first consistent point of the file system was captured at a first given point in time, wherein the second prime represents a second consistent point of the file system that was captured at a second given point in time prior to the first given point in time, and

determining at least a first of the prime segments that has not been previously verified, without verifying a second of the prime segments that has been previously verified, wherein verifying the first of the prime segments and the second of the prime segments includes determining whether the first and the second of the prime segments exist in their respective storage units, wherein the first prime, when at least the first prime segment has been successfully verified, can be used to construct the first consistent point of the file system for a purpose of restoring the file system to a known consistent point, wherein the first prime segment is only stored in the first storage unit and the second prime segment is only stored in the second storage unit; and

a cache coupled to the archiver configured to cache the second prime as an installable prime, wherein the second prime being collectively represented by a plurality of prime segments of which each of the prime segments has been verified, wherein a prime segment included in the plurality of prime segments collectively representing the second prime is not to be verified again for a purpose of verifying the first prime.

12. The system of claim 11 , wherein each of the first and second primes is represented by a prime dependency list having a plurality of entries which represent the plurality of prime segments collectively representing each of the first and second primes.

13. The system of claim 12 , wherein each of the entries in the prime dependency list comprises a prime set identifier (ID) associated with a storage unit ID indicating that a prime segment identified by the prime segment ID is supposed to be stored in one of the storage units identified by the storage unit ID.

14. The system of claim 13 , wherein determining whether a prime segment has been previously verified further comprises matching the prime segment ID and the storage unit ID in each entry between dependency lists of the first and second primes.