On-demand snapshot and prune in a data storage system

1. A method of data progression in a data storage system having at least two tiers of storage space, a first tier comprising storage space in a single level cell (SLC) solid state device (SSD) and a second tier comprising storage space in a multi-level cell (MLC) SSD, the method comprising:

setting a predetermined free space threshold for the first tier of storage space that is a threshold relating to the amount of free space available on the first tier of storage space;

monitoring at least an amount of available free space in the first tier of storage space;

when the amount of available free space in the first tier of storage space decreases to the predetermined free space threshold, generating an on-demand snapshot of at least a portion of the data of the first tier of storage space by designating that data as read-only;

transferring the on-demand snapshot to the second tier of storage space, thereby freeing the corresponding at least a portion of data of the first tier of storage space for new writes;

wherein a write operation received by the data storage system directed to data stored by the on-demand snapshot is directed instead to newly allocated storage space of the first tier of storage space, and the corresponding data in the on-demand snapshot is considered to be overwritten; and

when a page of the on-demand snapshot contains overwritten data, freeing that page of the on-demand snapshot, such that the page is no longer associated with the on-demand snapshot;

wherein the on-demand snapshot is utilized internally by the data storage system and is not generally accessible by a user of the data storage system.

2. The method of data progression of claim 1 , further comprising, in addition to generating an on-demand snapshot, generating snapshots of at least a portion of the data of the first tier of storage space and transferring at least some of the generated snapshots to the second tier of storage space at regular intervals.

3. The method of data progression of claim 1 , wherein the storage space of the SLC SSD is configured as RAID 10 storage.

4. The method of data progression of claim 3 , wherein the storage space of the MLC SSD is configured as RAID 5 storage.

5. The method of data progression of claim 1 , wherein the data storage system stores data for a plurality of logical volumes, and wherein the on-demand snapshot comprises data from a first of the logical volumes utilizing the most storage space in the first tier.

6. The method of data progression of claim 1 , wherein the page of the on-demand snapshot is freed substantially as soon as the corresponding data is overwritten.

7. The method of data progression of claim 1 , wherein the page of the on-demand snapshot is freed according to a batch pruning method that operates on at least a portion of the second tier of storage space as a batch and frees multiple pages of the batch, each page containing data considered to be overwritten.

8. The method of data progression of claim 7 , wherein the batch pruning method is triggered when the amount of available free space in the second tier of storage space decreases to a predetermined free space threshold for the second tier of storage space.

9. The method of data progression of claim 7 , wherein the batch pruning method is triggered according to a periodic schedule.

10. An information handling system comprising:

a data storage subsystem having at least two tiers of storage space, a first tier comprising storage space in a single level cell (SLC) solid state device (SSD) and a second tier comprising storage space in a multi-level cell (MLC) SSD;

a controller managing the data storage subsystem and configured to:

monitor at least an amount of available free space in the first tier of storage space;

when the amount of available free space in the first tier of storage space decreases to a predetermined free space threshold, generate an on-demand snapshot of at least a portion of the data of the first tier of storage space by designating that data as read-only;

transfer the on-demand snapshot to the second tier of storage space, thereby freeing the corresponding at least a portion of data of the first tier of storage space for new writes;

when a write operation is received by the data storage system directed to data stored by the on-demand snapshot, direct the write operation to newly allocated storage space of the first tier of storage space, and the corresponding data in the on-demand snapshot is considered to be overwritten; and

when a page of the on-demand snapshot contains overwritten data, free that page of the on-demand snapshot, such that the page is no longer associated with the on-demand snapshot;

wherein the on-demand snapshot is utilized internally by the controller and is not generally accessible by a user of the data storage subsystem.

11. The information handling system of claim 10 , wherein the storage space of the SLC SSD is configured as RAID 10 storage.

12. The information handling system of claim 11 , wherein the storage space of the MLC SSD is configured as RAID 5 storage.

13. The information handling system of claim 10 , wherein the controller is configured to free the page of the on-demand snapshot according to a batch pruning method that operates on at least a portion of the second tier of storage space as a batch and frees multiple pages of the batch, each page containing data considered to be overwritten.

14. The information handling system of claim 13 , wherein the controller runs the batch pruning method according to a periodic schedule.