Systems and methods for a read only mode for a portion of a storage system
View Patent ↗In general, embodiments of the invention relate to reading data from and writing data to a storage system. Specifically, embodiments of the invention relate to a read only mode for a portion of a storage system. In one embodiment, a selective read-only mode for a portion of a storage system is implemented by monitoring a condition that may affect a subset of persistent storage in a storage system, by detecting the condition, by entering a read-only mode for the subset, and by enforcing a policy of processing write requests and read requests to the storage system, which includes processing the write requests without modifying user data stored on the subset and processing the read requests, including requests for user data stored on the subset.
1. A method of entering a read-only mode for a portion of a storage system, comprising:
marking as unwritable a transaction journal associated with a portion of a storage system entering a read-only mode;
backing up the transaction journal without writing to the portion;
continuing to process, by one or more computer processors, unresolved transactions affecting the portion by marking as commit deferred, without writing to the transaction journal, those transactions for which a commit message is received after entering the read-only mode; and
processing, by one or more computer processors, those transactions marked commit deferred, after leaving the read-only mode for the portion, by marking each of those transactions as committed in the transaction journal, and sending committed messages to other affected portions of the storage system.
2. The method of claim 1 , further comprising continuing to process unresolved transactions affecting the portion by storing in memory, without writing to the transaction journal, a queue of deferred writes to the transaction journal associated with an abort message for an unresolved transaction received after entering the read-only mode for the portion.
3. The method of claim 2 , further comprising processing the deferred writes in the queue, after leaving the read-only mode for the portion, by writing the deferred writes in the transaction journal.
4. A non-transitory computer-readable medium having instructions stored thereon, the instructions comprising the method of claim 1 .
5. The method of claim 1 , further comprising invalidating the backup of the transaction journal after leaving the read-only mode for the portion.
6. The method of claim 1 , further comprising deferring one or more writes to at least one transaction journal associated with another portion of the storage system until the portion entering the read-only mode leaves the read-only mode.
7. The method of claim 1 , further comprising deferring one or more messages between the portion entering the read-only mode and another portion of the storage system until the portion entering the read-only mode leaves the read-only mode.
8. The method of claim 2 , further comprising maintaining states of the unresolved transactions on the memory.
9. The method of claim 8 , further comprising maintaining copies of data values associated with the unresolved transactions on the memory.
10. The method of claim 1 , wherein continuing to process unresolved transactions affecting the portion comprises:
maintaining a transaction block for each unresolved transaction, the transaction block stored on a memory and comprising an indication of a state of the corresponding unresolved transaction; and
if a commit message is received for a transaction while in the read-only mode for the portion, updating the indication of the state of that transaction in the corresponding transaction block.
11. The method of claim 10 , wherein states of the unresolved transactions correspond to states in a commit protocol.
12. The method of claim 10 , wherein processing those transactions marked commit deferred, after leaving the read-only mode for the portion, comprises traversing transaction blocks for each unresolved transaction.
13. The method of claim 10 , wherein continuing to process unresolved transactions affecting the portion further comprises, if an abort message is received for a transaction while in the read-only mode for the portion, storing a deferred write on the memory, the deferred write comprising an indication that an abort message was received for that transaction.
14. The method of claim 13 , further comprising, after leaving the read-only mode for the portion, aborting those transactions for which a deferred write is stored on the memory.
15. The method of claim 1 , wherein the transaction journal comprises transaction blocks, each transaction block associated with at least one unresolved transaction and comprising an indication of a state of the associated at least one unresolved transaction.
16. The method of claim 15 , further comprising maintaining a queue of deferred writes to the transaction journal.
17. The method of claim 16 , wherein one or more of the deferred writes comprises a command to unlink one or more transaction blocks from the transaction journal.
18. The method of claim 1 , wherein entering the read-only mode for the portion occurs before the portion has been mounted into the storage system.
19. The method of claim 1 , wherein entering the read-only mode for the portion occurs after the portion has been mounted into the storage system.
20. The method of claim 1 , wherein the backup of the transaction journal is invalidated after leaving the read-only mode for the portion.