Tracking in-progress writes through use of multi-column bitmaps
View Patent ↗Disclosed is a method and apparatus for tracking in-progress writes to a data volume and a copy thereof using a multi-column bit map. The method can be implemented in a computer system and, in one embodiment, includes creating a data volume in a first memory, and creating a copy of the data volume in a second memory. In response to the computer system receiving a request to write first data to the data volume, the computer system switches the state of first and second bits of a map entry in a memory device, wherein the state of the first and second bits are switched using a single write access to the memory device.
1. A method comprising:
creating a data volume;
creating a copy of the data volume;
a computer system receiving a request to write first data to the data volume;
switching the state of a pair of bits in a memory device in response to the computer system receiving the request to write first data to the data volume, wherein the state of the pair of bits are switched using a single write access to the memory device.
2. The method of claim 1 further comprising allocating memory of the memory device for a map, wherein the map comprises an entry, wherein the entry comprises the pair of bits.
3. The method of claim 1 further comprising:
writing the first data to a memory block in a first memory, wherein the first memory is configured to store the data volume;
writing the first data to a memory block in a second memory, wherein the second memory is configured to store the data volume copy;
switching the state of one or the pair bits back to its original state after writing the first data to the memory blocks of the first and second memory.
4. The method of claim 3 :
wherein a first bit of the pair, when switched to a first or second state, indicates that data has been written to the first memory after allocation of the memory for the map;
wherein a second bit of the pair, when switched to a first or second state, indicates that the first and second memories will be subject to a write operation.
5. A computer readable medium comprising instructions executable by a computer system, wherein the computer system performs a method in response to executing the instructions, the method comprising:
creating a data volume;
creating a copy of the data volume;
switching the state of a pair of bits in a memory device in response to the computer system receiving a request to modify first data of the data volume, wherein the state of the pair of bits are switched using a single write access to the memory device.
6. The computer readable medium of claim 5 , wherein the method further comprises allocating memory of a memory device for a map, wherein the map comprises an entry, wherein the entry comprises the pair of bits.
7. The computer readable medium of claim 6 wherein the method further comprises:
modifying the first data, wherein the first data is stored in a memory block in a first memory, wherein the first memory is configured to store the data volume;
modifying data in a second memory, wherein the second memory is configured to store the data volume copy;
switching the state of one bit of the pair back to its original state after modifying data in the second memory.
8. The computer readable medium of claim 6 :
wherein one bit of the pair, when switched to a first or second state, indicates that data in the first memory was modified after allocation of the memory for the map;
wherein the other bit of the pair, when switched to a first or second state, indicates that the first and second memories are subject to write operation.
9. The computer readable medium of claim 6 wherein the method further comprises:
creating a map in the memory device, wherein the map comprises a plurality of entries, each entry comprising first, second, and third bits;
wherein each entry corresponds to a respective memory block of the data volume;
wherein each first bit, when set to a first or second state, indicates whether its respective memory block of the data volume stores valid data;
wherein each second bit, when set to a first or second state, indicates whether its respective memory block of the data volume stores data which has been modified since creation of the data volume copy;
wherein each third bit, when set to a first or second state, indicates whether its respective memory block of the data volume will be subject to a write operation, and;
wherein the pair of bits are the second and third bits, respectively, of one entry of the map.
10. A computer readable medium comprising instructions executable by a computer system, wherein the computer system performs a method in response to executing the instructions, the method comprising:
creating a data volume;
creating a mirror of the data volume;
creating a map in a memory device, wherein the map comprises a plurality of entries, wherein each entry comprises first and second bits;
wherein each first bit, when set to a first or second state, indicates whether data has been written to a respective block of the data volume since allocation of memory for the map;
wherein each second bit, when set to a first or second state, indicates whether respective blocks in the data volume and mirror will be subject to separate in-progress write operations.
11. The computer readable medium of claim 10 wherein each of the plurality of entries comprises a third bit, wherein the third bit, when set to a first or second state, indicates whether respective blocks in the data volume contains valid data.