System and method for handling I/O write requests
System and methods for managing I/O write requests of host systems to physical storage. A storage subsystem includes a plurality of storage devices where each storage device is configured to provide data storage. At least a pair of redundant controllers is connected to the plurality of storage devices for executing the I/O write requests from the host systems. A received I/O write request is initially saved in a controller memory of one of the controllers and mirrored in controller memory of the other controller. In one embodiment, the I/O write request is transferred to a flash memory device for subsequent transfer to the storage devices. Once transferred to the flash memory device, the I/O write request may be flushed from the controller memories. The I/O write request may then be transferred to the storage devices from the flash memory device as a background operation.
1. A method of managing write requests of a host system to a plurality of storage subsystems, each storage subsystem comprising a plurality of storage devices configured as one of more logical units configured for providing data storage and each storage subsystem further comprising a pair of storage controllers coupled to the storage devices, the method including:
receiving an I/O write request at a first storage controller of a storage subsystem, the I/O write request addressing a storage location for data within the storage devices of the storage subsystem;
allocating the I/O write request to a first set of allocated storage blocks in a first cache memory of the first controller and a second set of allocated storage blocks in a second cache memory of a second controller;
transferring the I/O write request to both a read cache and a mirror cache of a solid state drive (SSD), wherein the mirror cache mirrors unexecuted I/O write requests in the read cache of the SSD that address storage locations within the storage devices;
subsequent to transferring the I/O write request to the SSD, de-allocating the first and second sets of allocated storage blocks in the first and second cache memories of the first and second controllers and subsequent to transferring the I/O write request data to the storage devices of the storage subsystem, flushing the I/O write request from the mirror cache while maintaining the I/O write request in the read cache for subsequent access.
2. The method of claim 1 , further comprising:
determining, at one of the controllers, a level of cache utilization of the cache memory of the controller; and
upon determining the level of cache utilization being below a predetermined threshold, transferring the I/O write request to the storage devices directly from the controller.
3. The method of claim 1 , further comprising:
determining, at one of the controllers, a level of cache utilization of the cache memory of the controller; and
upon determining the level of cache utilization being above a predetermined threshold, simultaneously transferring the I/O write request to both of the read cache and mirror cache of the SSD.
4. The method of claim 1 , further comprising transferring the I/O write request from the mirror cache of the SSD to the storage devices.
5. The method during of claim 4 , wherein the I/O write request is transferred during idle of one of the first and second controllers.
6. The method of claim 4 , wherein the step of de-allocating occurs prior to the I/O write request being transferred to the storage devices from the mirror cache of the SSD.
7. The method of claim 1 , wherein the transferring step comprises:
transferring the I/O write request to first and second SSDs, wherein each SSD includes a read cache and a mirror cache, wherein a first mirror cache of the first SSD mirrors unexecuted I/O write requests in a second read cache of the second SSD and a second mirror cache of the second SSD mirrors unexecuted I/O write requests in a first read cache of the first SSD.
8. The method of claim 7 , wherein the transferring step comprises transferring the I/O write request to a read cache in a first of the SSDs and transferring the I/O write request to a mirror cache in a second of the SSDs.
9. The method of claim 7 , wherein the transferring step comprises transferring the I/O write request to a read cache and mirror cache of a first of the SSDs and transferring the I/O write request to a read cache and mirror cache of a second of the SSDs.