Service level agreement based management of pending access requests

1. A method for service level agreement allocation of permanent storage layer resources of a storage system, the method comprises:

monitoring, by a control layer of the storage system, actual performances of the storage system that are related to multiple logical volumes;

calculating actual-to-required relationships between the actual performances and service level agreement defined performances of the multiple logical volumes;

allocating, for different logical volumes of the multiple logical volumes, allowable amounts of pending access requests; wherein pending access requests are access requests waiting for response from a permanent storage layer of the storage system; wherein the allocating is based on, at least, the actual-to-required relationships;

receiving, by the control layer, received access requests aimed to one or more logical volumes of the logical volumes; and

sending to the permanent storage layer requests to serve at least some of the received access requests, based on the allowable amounts of pending access requests.

2. The method according to claim 1 comprising delaying, when an allowable amount of pending access requests related to a given logical volume was reached, a sending of a request to serve, by the permanent storage layer, an access request associated with the given logical volume.

3. The method according to claim 1 wherein the allocating comprises increasing an allowable amount of pending access requests associated with an underperforming logical volume of the multiple logical volumes.

4. The method according to claim 1 wherein the allocating comprises reducing an allowable amount of pending access requests associated with an over-performing logical volume of the multiple logical volumes.

5. The method according to claim 1 wherein the allocating is also based on pervious actual performances of the storage system related to the multiple logical volumes.

6. The method according to claim 1 , comprising calculating an effectiveness of an increment in an amount of pending access requests associated with a given under-performing logical volume.

7. The method according to claim 6 wherein the calculating of the effectiveness is based upon history related to the given under-performing logical volume.

8. The method according to claim 1 wherein the allocating is also based on previously allocated allowable amounts of access requests.

9. The method according to claim 1 wherein the calculating of the allowable amounts of pending access requests comprises assigning scores to the multiple logical volumes scores; wherein the scores are based on the actual-to-required relationships; and wherein the allowable amounts of pending access requests are based on the scores.

10. The method according to claim 9 wherein the allowable amounts of pending access requests are based on the scores and on previously allocated allowable amounts of pending access requests.

11. The method according to claim 1 , comprising re-allocating at least one allowable amount of pending access requests when one or more actual-to-required relationship has changed.

12. The method according to claim 1 wherein the control layer is prevented from directly defining resource allocations of resources of the permanent storage layer.

13. The method according to claim 1 wherein an actual-to-required relationship of a given logical volume is a ratio between an actual performance of the storage system that is related to the given logical volume and an SLA defined performance of the storage system that is related to the given logical volume.

14. The method according to claim 1 , comprising calculating an effectiveness of an increment in an amount of pending access requests associated with a given under-performing logical volume; wherein the allocating comprises decreasing an allowable amount of pending access requests associated with an over-performing logical volume instead of increasing an allowable amount of pending access requests associated with the given under-performing logical volume.

15. A storage system comprising a control layer and a permanent storage layer; wherein the control layer is configured to monitor actual performances of the storage system that are related to multiple logical volumes; calculate actual-to-required relationships between the actual performances and service level agreement defined performances of the multiple logical volumes; allocate, for different logical volumes of the multiple logical volumes, allowable amounts of pending access requests; wherein pending access requests are access waiting for response from the permanent storage layer of the storage system; wherein the allocating is based on, at least, the actual-to-required relationships; receive received access requests aimed to one or more logical volumes of the logical volumes; and (e) send to the permanent storage layer requests to serve at least some of the received access requests, based on the allowable amounts of pending access requests.

16. A non-transitory computer readable medium that stores instructions that once executed by a control layer of a storage system, causes the control layer to execute the steps of: monitoring, by a control layer of the storage system, actual performances of the storage system that are related to multiple logical volumes; calculating actual-to-required relationships between the actual performances and service level agreement defined performances of the multiple logical volumes; allocating, for different logical volumes of the multiple logical volumes, allowable amounts of pending access requests; wherein pending access requests are access requests waiting for response from the permanent storage layer of the storage system; wherein the allocating is based on, at least, the actual-to-required relationships; receiving, by the control layer, received access requests aimed to one or more logical volumes of the logical volumes; and sending to the permanent storage layer requests to serve at least some of the received access requests, based on the allowable amounts of pending access requests.