Method of detection of data corruption in mirrored storage
A first read request is received from a computer system. Data from one mirror of a data volume is returned to the computer system in response to receiving the first read request. The computer system may check the returned data to determine whether it is corrupted. If corrupted, the computer system sends a second read request for the same data. Rather than returning the same corrupted data stored in the one mirror, a copy of the requested data is returned from an alternate mirror of the data volume.
1. A method comprising:
receiving a first read request, wherein the first read request is received from a computer system;
reading data from a mirror of a data volume in response to receiving the first read request;
receiving a second read request, wherein the second read request is received from the computer system, wherein the second read request is received subsequent to the first read request, and wherein the first and second read requests are for the same data;
reading data stored in an alternate mirror of the data volume in response to receiving the second read request.
2. The method of claim 1 further comprising:
comparing an identification of data sought by the first read request with data identifications stored in a searchable data structure that stores a history of read requests in memory;
wherein data is read from the mirror of the data volume in response to determining that the identification of data sought by the first read request is not stored in the history of read requests.
3. The method of claim 2 further comprising creating a new entry in the history of read requests, wherein the entry comprises the identification of data sought by the first read request, the time of the read request, and a list of mirrors from which the data has been returned.
4. The method of claim 3 further comprising comparing the identification of data sought by the second read request with data identifications stored in the history of read requests.
5. The method of claim 4 further comprising identifying a mirror that has not yet been marked as read in the history of read requests.
6. The method of claim 5 further comprising reading the identified mirror and adding its identity to the list of read mirrors in the history of reads entry corresponding to the identification of data and updating the timestamp on the history entry to the time of the new read.
7. The method of claim 1 further comprising:
the computer system processing the data read from the mirror of the data volume;
the computer system generating the second read request in response to determining that the data read from the mirror of the data volume is corrupted.
8. The method of claim 3 wherein data is read from the alternate mirror only if a current time is within a predetermined amount of time of a time stamp.
9. A computer readable medium comprising instructions executable by a first computer system, wherein the first computer system performs a method in response to executing the instructions, the method comprising:
receiving a first read request, wherein the first read request is received from a second computer system;
reading data from a mirror of a data volume in response to receiving the first read request;
receiving a second read request, wherein the second read request is received from the second computer system, wherein the second read request is received subsequent to the first read request, and wherein the first and second read requests are for the same data;
reading data stored in an alternate mirror of the data volume in response to receiving the second read request.
10. The computer readable medium of claim 9 wherein the method further comprises:
comparing an identification of data sought by the first read request with data identifications stored in a searchable data structure that stores a history of read requests in memory;
wherein data is read from the mirror of the data volume in response to determining that the identification of data sought by the first read request is not stored in the history of read requests.
11. The computer readable medium of claim 10 wherein the method further comprises comprising creating a new entry in the history of read requests, wherein the entry comprises the identification of data sought by the first read request, the time of the read request, and a list of mirrors from which the data has been returned.
12. The computer readable medium of claim 10 wherein the method further comprises comparing the identification of data sought by the second read request with data identifications stored in the history of read requests.
13. The computer readable medium of claim 12 wherein the method further comprises identifying a mirror that has not yet been marked as read in the corresponding entry in the history of read requests.
14. The computer readable medium of claim 12 wherein the method further comprises reading the identified mirror and adding its identity to the list of read mirrors in the entry in the history of read requests corresponding to the identification of data and updating the timestamp on the history entry to the time of the new read.
15. The computer readable medium of claim 9 wherein the method further comprises comparing time T 1 with time T 2 , wherein time T 1 is the time when the first request was received, and wherein time T 2 is the time when the second request was received.
16. The computer readable medium of claim 15 wherein the method further comprises reading the data stored in the mirrored copy in response to receiving the second request only if time T 2 occurs within a predetermined amount of time after T 1 .
17. A data processing system comprising;
a first computer system coupled to a memory system, wherein the memory system stores a mirrored data volume, wherein the first computer system comprises a memory for storing instructions executable by the first computer system, wherein the first computer system implements a method in response to executing the instructions, the method comprising:
receiving a first read request, wherein the first read request is received from a second computer system;
reading data from a first mirror of the mirrored data volume in response to receiving the first read request;
receiving a second read request, wherein the second read request is received from the second computer system, wherein the second read request is received subsequent to the first read request, and wherein the first and second read requests are for the same data;
reading data stored in a second mirror of the mirrored data volume in response to receiving the second read request.