Methods and apparatus for time-based dynamically adjusted journaling

1. A data center for data backup and replication, comprising:

a pool of multiple variable-size storage units for storing a journal of I/O write commands issued at respective times, wherein the journal spans a history window of a pre-specified time length, wherein the variable-size storage units comprise variable-size data chunks corresponding to a window of time, and wherein the pool of storage units is not dedicated to the journal; and

a journal manager for dynamically allocating more variable-size data chunks of the variable-size storage units for storing the journal as the journal size increases, and for dynamically releasing variable-size data chunks of the variable-size storage units as the journal size decreases.

2. The data center of claim 1 wherein said journal manager enforces a pre-specified maximum size constraint on the journal.

3. The data center of claim 1 wherein said storage units are virtual storage units.

4. The data center of claim 1 wherein said storage units are physical storage units.

5. The data center of claim 1 , wherein said journal manager establishes a maintenance history indicating a timeframe for how long write commands are saved in the journal.

6. A computer-based method for a data center, comprising:

receiving, by a computer at a sequence of times, new data to add to a journal, the journal comprising one or more allocated variable-size data chunks corresponding to a window of time from variable-size storage resources from a pool of resources that are not dedicated to the journal, and wherein journal data is stored in the allocated variable-size data chunks and promoted from time to time to a recovery disk;

determining, by the computer, if the journal already contains data for an entire pre-designated time history;

additionally determining, by the computer, if the addition of the new data to the journal would cause the journal to exceed a pre-designated maximum size;

further determining, by the computer, if the additional of the new data to the journal requires allocating an additional variable-sized data chunk to the journal;

when said further determining is affirmative, then yet further determining, by the computer, if the pool of resources has a free variable-sized data chunk available;

when said determining or said additionally determining or said yet further determining is affirmative, then:

promoting, by the computer, old time data from the journal to a recovery disk;

removing, by the computer, the old time data from the journal; and

releasing, by the computer, one or more of the variable-size data chunks from the journal, if all of the data from the one or more variable-size data chunks was promoted to the recovery disk;

when said further determining is affirmative, then allocating, by the computer, an additional variable-sized data chunk to the journal; and

adding, by the computer, the new data to the journal.

7. The method of claim 6 wherein the new data comprises one or more write requests to a disk.

8. The method of claim 6 further comprising:

further receiving, by the computer at a sequence of times, test data to add to the journal, during a test period;

further allocating, by the computer, one or more additional variable-size data chunks to the journal, for storage of test data;

further adding, by the computer, the test data to the one or more additional variable-size data chunks; and

further releasing, by the computer, the one or more additional variable-size data chunks upon completion of the test period, wherein said receiving, said allocating, said adding and said releasing are also performed for production data during the test period.

9. The method of claim 6 , comprising:

establishing a maintenance history indicating a timeframe for how long write commands are saved in the journal.

10. A method of data backup and replication, comprising:

accessing a pool of multiple variable-size storage units for storing a journal of I/O write commands issued at respective times, wherein the journal spans a history window of a pre-specified time length, wherein the variable-size storage units comprise variable-size data chunks corresponding to a window of time, and wherein the pool of storage units is not dedicated to the journal;

dynamically allocating more variable-size data chunks from the pool of multiple variable-size storage units for storing the journal as the journal size increases; and

dynamically releasing variable-size data chunks from the pool of multiple variable-size storage units as the journal size decreases.

11. The method of claim 10 further comprising enforcing a pre-specified maximum size constraint on the journal.

12. The method of claim 10 , comprising:

establishing a maintenance history indicating a timeframe for how long write commands are saved in the journal.