Multi-stage slice recovery in a dispersed storage network
A computing device for use in a dispersed storage network (DSN) to recover corrupt encoded data slices. The computing device requests, from storage units of the DSN, encoded data slices corresponding to a data segment. In response, the computing device receives at least a decode threshold number of encoded data slices and at least one integrity error message that provides an indication of a corrupt encoded data slice, such that less than a decoded threshold number of valid slices is received. Utilizing at least one correction approach, which may involve stored integrity data, the computing device corrects the corrupt slice(s) to produce a decode threshold number of encoded data slices in order to decode the corresponding data segment. A variety of correction approaches may be employed, including a multi-stage approach that utilizes data from both valid and invalid slices.
1. A computing device comprises:
an interface;
memory that stores operational instructions; and
a processing module operably coupled to the interface and the memory, wherein the processing module is configured to execute the operational instructions to:
transmit to a set of storage units of a storage network, via the interface, a request for encoded data slices, wherein each of the encoded data slices includes an encoded portion of a corresponding data segment;
receive, via the interface, less than a decode threshold number of requested encoded data slices and at least one integrity error message from the set of storage units, wherein the at least one integrity error message provides an indication of a corrupt encoded data slice;
request, via the interface, at least one corrupt encoded data slice from the set of storage units;
receive, via the interface, the at least one corrupt encoded data slice; and
correct the at least one corrupt encoded data slice, utilizing at least one correction approach, to produce at least a decode threshold number of encoded data slices.
2. The computing device of claim 1 , wherein the processing module is further configured to execute the operational instructions to:
decode the decode threshold number of encoded data slices to generate the corresponding data segment.
3. The computing device of claim 1 , wherein correction of the at least one corrupt encoded data slice includes:
selecting a first correction approach based on stored integrity information;
attempting to correct the at least one corrupt encoded data slice using the first correction approach;
in response to determining that the first correction approach was not successful, selecting a second correction approach based on the stored integrity information; and
correcting the at least one corrupt encoded data slice using the second correction approach.
4. The computing device of claim 1 , wherein the at least one correction approach utilizes slice substitution and stored integrity information corresponding to a pre-encoded version of the corresponding data segment.
5. The computing device of claim 1 , wherein the local memory includes integrity information corresponding to a pre-encoded version of the corresponding data segment, wherein the at least one correction approach includes applying the integrity information to determine if the at least one corrupt encoded data slice is valid.
6. The computing device of claim 1 , wherein the at least one correction approach includes byte-by-byte recovery of the at least one corrupt encoded data slice utilizing valid bytes, in a common byte position, from a decode threshold number of encoded data slices.
7. The computing device of claim 1 , wherein the at least one correction approach utilizes integrity information regarding the corresponding data segment.
8. The computing device of claim 1 , wherein the at least one correction approach utilizes integrity information generated by a dispersed storage error encoding process during encoding of the encoded data slices.
9. The computing device of claim 1 , wherein the at least one correction approach utilizes integrity information regarding individual ones of the encoded data slices generated prior to storage of the encoded data slices in the set of storage units.