Log record parsing for a distributed log on a disk array data storage system

A method of recovering a storage system having multiple storage media following a failure, wherein the storage system maintains a log image having first log records kept in a first log and second log records kept in a second distributed log that is distributed over the storage media, the method comprising:

• reading the first log records of the first log to reproduce a part of the log image;
• and
• scanning the distributed log to locate any second log records to reproduce a remainder of the log image;
• wherein the first and second log records are assigned sequence numbers and the scanning comprises determining a most recent first log record in the first log and searching the distributed log to locate a next log record from among the second log records that has a more recent sequence number than that of the first log record.

In a storage system that maintains a log image having first log records kept in a first log and second log records kept in a distributed log that is distributed over the storage media, wherein each of the storage media includes a reserved area that form the distributed log, each of the reserved areas having at least two staging buffers that are alternately written to and wherein the first and second log records are assigned sequence numbers, a method of recovering the log image following a failure, comprising:

• reading the first log records of the first log to reproduce a part of the log image;
• scanning the first log records to locate a most recent log record having a most recent sequence number from among the sequence numbers assigned to the first log records;
• reading individual ones of the staging buffers;
• incrementally selecting ones of the second log records stored in the staging buffers;
• evaluating whether a selected one of the second log records is a next log record having a next sequence number that follows from the most recent sequence number associated with the most recent log record among the first log records;
• and
• upon locating the next log record on a particular storage media, commencing a search to look for a subsequent log record with a next sequence number on the particular storage media that contains the log record just found, but in the other staging buffer on the particular storage medium.

A storage system comprising:

• a memory to hold a log image having multiple log records, the log records having associated sequence numbers that indicate a temporal order among the log records;
• multiple storage media connected to the memory, each of the storage media having a reserved area that defines at least two staging buffers;
• a page log stored on the storage media, the page log containing one or more pages of the log records from the log image;
• a distributed log distributed over the storage media and residing in the staging buffers, the distributed log containing log records that are occasionally written to one of the storage media in an alternating pattern between the two staging buffers, wherein the log records in the distributed log may include more recent log records that have been more recently written to the log image than the log records contained in the page log;
• and
• a log recovery manager to recover the log image following a failure, the log recovery manager reading the log records from the page log to reproduce a part of the log image and subsequently scanning the distributed log to locate any more recent log records to reproduce a remainder of the log image.

In a storage system that maintains a log image having first log records kept in a first log and second log records kept in a distributed log that is distributed over the storage media, wherein each of the storage media includes a reserved area that form the distributed log, each of the reserved areas having at least two staging buffers that are alternately written to and wherein the first and second log records are assigned sequence numbers, a computer-readable storage medium comprising computer-executable instructions for:

• reading the first log records of the first log to reproduce a part of the log image;
• scanning the first log records to locate a most recent log record having a most recent sequence number from among the sequence numbers assigned to the first log records;
• reading individual ones of the staging buffers;
• incrementally selecting ones of the second log records stored in the staging buffers;
• evaluating whether a selected one of the second log records is a next log record having a next sequence number that follows from the most recent sequence number associated with the most recent log record among the first log records;
• and
• upon locating the next log record on a particular storage media, commencing a search to look for a subsequent log record with a next sequence number on the particular storage media that contains the log record just found, but in the other staging buffer on the particular storage medium.