I/O scheduling for flash drives
In a data storage system, a controller schedules I/Os to storage devices so that each one substantially performs only reads or only writes, thereby increasing performance. At least one storage device is designated as a current write device. The remainder of the devices are designated current read devices. Host write data is stored in a buffer memory. Storage device reads occur only from the current read devices. Storage device writes occur only to the current write device(s). In response to a triggering event, the designations are updated so that a different storage device is designated the current write device, and the remainder of the storage devices are designated the current read devices. A triggering event may include but not be limited to a time period, number of writes, cache size, device wear, environmental conditions, application requirements, or combination.
1. Apparatus for controlling the scheduling of data transfers between a buffer memory and a plurality of solid state storage devices in a data storage system, the apparatus comprising:
a controller for designating at least one of the plurality of solid state storage devices as a current write device such that there is always at least one solid state storage device scheduled as a current write device;
the controller designating the remainder of the plurality of solid state storage devices as current read device(s);
the controller storing write data from a host in the buffer memory;
the controller allowing storage device reads to occur only from the current read device(s);
the controller allowing storage device writes to occur only to the current write device(s) and to any available address location of the current write device(s);
the controller, responsive to a triggering event, updating the designations to cause a different and at least one of the plurality of solid state storage devices to be designated a new current write device, and the remainder of the plurality of solid state storage devices to be designated the current read device(s), wherein, as prerequisite to accomplishing the update of the designations, the controller allows write operations pending for each current write device to finish to that current write device and reads to occur from any of the solid state storage devices, including from each current write device.
2. The apparatus of claim 1 wherein the triggering event comprises a time period, or a number of host writes, or a number of storage device writes, or cache size, or storage device wear, or environmental conditions, or application specific requirements, or on demand from an operator, or based on policies set for logical volumes to meet availability objectives, or based on reactive or predictive algorithmic attempts to optimize performance, or any combination thereof.
3. The apparatus of claim 2 wherein the controller comprises, for each of the at least one current write device, logic for:
designating a current read device as a new current write device;
waiting for pending write operations on the at least one current write device to finish;
designating the at least one current write device as at least one new current read device;
designating the new current write device as one of the at least one current write device.
4. The apparatus of claim 1 wherein the solid state storage devices are arranged as a RAID 1, RAID 5, or RAID 6 data storage array.
5. A method of scheduling data transfers between a buffer memory and a plurality of solid state storage devices in a data storage system, the method comprising the steps of:
designating at least one of the plurality of solid state storage devices as a current write device such that there is always at least one solid state storage device scheduled as a current write device;
designating the remainder of the plurality of solid state storage devices as current read device(s);
storing write data from a host in the buffer memory;
allowing storage device reads to occur only from the current read device(s);
allowing storage device writes to occur only to the current write device(s) and to any available address location of the current write device(s);
updating the designations in response to a triggering event to cause a different at least one of the plurality of solid state storage devices to be designated a new current write device, and the remainder of the plurality of solid state storage devices to be designated a new current read device; and
allowing, as prerequisite to accomplishing the updating of the designations, write operations pending for each current write device to finish to that current write device and reads to occur from any of the solid state storage devices, including from each current write device.
6. The method of claim 5 wherein the triggering event comprises a time period, or a number of host writes, or a number of storage device writes, or cache size, or storage device wear, or environmental conditions, or application specific requirements, or on demand from an operator, or based on policies set for logical volumes to meet availability objectives, or based on reactive or predictive algorithmic attempts to optimize performance, or any combination thereof.
7. The method of claim 6 wherein the step of updating comprises, for each of the at least one current write device, the steps of:
designating a current read device as a new current write device;
waiting for the pending write operations on the at least one current write device to finish;
designating the at least one current write device as at least one new current read device;
designating the new current write device as one of the at least one current write device.
8. The method of claim 5 wherein the solid state storage devices are arranged as a RAID 1, RAID 5, or RAID 6 data storage array.
9. Apparatus for controlling the scheduling of data transfers between a buffer memory and a mirrored pair of solid state storage devices in a data storage system, the apparatus comprising:
a controller designating one of the solid state storage devices in the mirrored pair as the current write device such that there is always at least one solid state storage device scheduled as a current write device;
the controller designating the other solid state storage device in the mirrored pair as the current read device;
the controller storing write data from a host in the buffer memory;
the controller allowing storage device reads to occur only from the current read device to the buffer memory;
the controller allowing storage device writes to occur from the buffer memory only to the current write device and to any available address location of the current write device;
the controller operable upon the occurrence of a triggering event to perform a swap operation such that the current write device becomes a new current read device and the current read device becomes a new current write device, wherein, as prerequisite to accomplishing the swap operation, the controller allows write operations pending for the current write device to finish to the current write device and reads to occur from any of the solid state storage devices, including from the current write device.
10. The apparatus of claim 9 wherein the triggering event comprises a time period, or a number of host writes, or a number of storage device writes, or cache size, or storage device wear, or environmental conditions, or application specific requirements, or on demand from an operator, or based on policies set for logical volumes to meet availability objectives, or based on reactive or predictive algorithmic attempts to optimize performance, or any combination thereof.
11. The apparatus of claim 10 wherein the controller to perform a swap comprises logic for:
designating the current read device as the new current write device;
waiting for the pending write operations on the current write device to finish;
designating the current write device as the new current read device;
designating the new current write device as the current write device.
12. A method for controlling the scheduling of data transfers between a buffer memory and a mirrored pair of solid state storage devices in a data storage system, the method comprising the steps of:
designating one of the solid state storage devices in the mirrored pair as the current write device such that there is always one solid state storage device scheduled as a current write device;
designating the other solid state storage device in the mirrored pair as the current read device;
storing write data from a host in the buffer memory;
allowing storage device reads to occur only from the current read device to the buffer memory;
allowing storage device writes to occur from the buffer memory only to the current write device and to any available address location of the current write device;
performing a swap operation upon the occurrence of a triggering event such that the current write device becomes a new current read device and the current read device becomes a new current write device; and
as prerequisite to accomplishing the performing of the swap operation, allowing write operations pending for the current write device to finish to the current write device and reads to occur from either of the solid state storage devices, including from the current write device.
13. The method of claim 12 wherein the triggering event comprises a time period, or a number of host writes, or a number of storage device writes, or cache size, or storage device wear, or environmental conditions, or application specific requirements, or on demand from an operator, or based on policies set for logical volumes to meet availability objectives, or based on reactive or predictive algorithmic attempts to optimize performance, or any combination thereof.
14. The method of claim 13 wherein the step to perform a swap comprises the steps of:
designating the current read device as the new current write device;
waiting for the pending write operations on the current write device to finish;
designating the current write device as the new current read device;
designating the new current write device as the current write device.