Write-through-and-back cache

Abstract

Embodiments are provided for cache memory systems. In one general embodiment, a system that includes a storage device, and at least one storage class memory device operating as a write cache for the storage device. The storage device further includes a first storage location for data received from a host computer during a host write request and a second storage. Data received from a host write request is written to the storage class memory device, to the first location in the storage device, and to the second location in the storage device that logically reflects the location of the data in the storage class device location configured as a log structured file.

1 . A system comprising:
 a storage device; and   at least one storage class memory device operating as a write cache for the storage device; the storage device further comprising:
 a first storage location for storing data received from a host computer during a host write request; and 
 a second storage location; 
 wherein data received from a host write request is written to the storage class memory device, to the first location in the storage device, and to the second location in the storage device that logically reflects the location of the data in the storage class device. 
   
     
     
         2 . The system of  claim 1 , wherein the second storage location is configured as a log structured file and wherein data is sequentially written to the log structured file after a host write request is performed. 
     
     
         3 . The system of  claim 2 , wherein a second write of data to the storage device after a host write request is to a logical block address in the storage device, wherein the logical block address is specified in the host write request. 
     
     
         4 . The system of  claim 3 , wherein the reliability of the system is unaffected by either a storage class memory device having lower reliability than a reliability of the storage class memory device or by a storage class memory device having lower reliability than a reliability of the storage device. 
     
     
         5 . The system of  claim 3 , wherein data in the storage class memory is read to determine if a cache hit occurs after a read request from a host computer. 
     
     
         6 . The system of  claim 5 , wherein data in the storage class memory is read to serve a cache hit after a read request from a host computer. 
     
     
         7 . The system of  claim 3 , wherein data stored in the system is protected against loss unless data in the storage class memory and data in the second storage location are both lost. 
     
     
         8 . The system of  claim 3 , wherein data stored in the system comprises data sent from a host computer during a host write request and metadata. 
     
     
         9 . The system of  claim 8 , wherein metadata is protected against loss unless data in the storage class memory and data in the second storage location are both lost. 
     
     
         10 . The system of  claim 3 , wherein data is read from the second storage location only when data is to be recovered following a loss of data from the storage class memory or from the storage device. 
     
     
         11 . The system of  claim 3 , wherein the storage device comprises a plurality of storage devices arranged in a selected Redundant Array of Independent Disks (RAID) configuration. 
     
     
         12 . A computer system comprising:
 a write-through-and-back cache; and   a plurality of storage devices arranged in a selected Redundant Array of Independent Disks configuration,   wherein data received by the write-through-and-back cache is stored in the write-through-and-back cache and in two different storage locations in the storage devices, and wherein a second storage location of the two different storage locations a second storage location logically reflects the location of the data in a storage class device of the write-through-and-back cache.   
     
     
         13 . The computer system of  claim 12 , wherein the write-through-and-back cache further comprises:
 a storage buffer adapted to receive input data corresponding to a write request from a host computer;   at least one storage class memory in data communication with the storage buffer and adapted to receive input data from the write request; and   a dynamic random access buffer in data communication with the storage class memory and with the storage devices.   
     
     
         14 . The computer system of  claim 13 , further comprising:
 at least one storage device of the Redundant Array of Independent Disks including a sequential log file adapted for log-structured sequential writes; and   data received from the host during a host write request is written to the storage class memory device, to the sequential log file, and to another storage device location.   
     
     
         15 . The computer system of  claim 14 , wherein data in the storage class memory is log-structured and data in the write-through-and-back cache and the sequential log are mirrors of each other, thereby avoiding a need to track which data has been written to any of the plurality of storage devices. 
     
     
         16 . A computer program product, comprising:
 a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising:   computer readable program code configured to receive a host write request from a host computer;   computer readable program code configured to create a sequential log file in a storage device;   computer readable program code configured to copy data received during the host write request to a storage buffer;   computer readable program code configured to determine if a selected quantity of data has been accumulated in the storage buffer; and   computer readable program code configured to execute a write through of data to sequentially write the data accumulated in the storage buffer to the sequential log file and to a storage class memory device if the selected quantity of data has been accumulated in the storage buffer/   
     
     
         17 . The computer program product of  claim 16 , further comprising:
 computer readable program code configured to receive a host write request from the host computer if the selected quantity of data has not been accumulated in the storage buffer;   computer readable program code configured to execute a write back of data if it is determined that data is to be destaged from the storage class memory device; and   computer readable program code configured to write the data to a logical block address in the storage device specified by the host write request.   
     
     
         18 . The computer program product of  claim 16 , further comprising:
 computer readable program code configured to limit reading of the sequential log file to recovery of data lost from either the storage class memory or the storage device.   
     
     
         19 . The computer program product of  claim 16 , further comprising:
 computer readable program code configured to locate the sequential log file and data received during a host write request on separate storage devices.   
     
     
         20 . The computer program product of  claim 16 , further comprising:
 computer readable program code configured to operate a write-through-and-back cache;   computer readable program code configured to operate at least one storage class memory device to communicate with the storage buffer and configured to receive input data from the write request; and   computer readable program code configured to operate a dynamic random access buffer in communication with the storage class memory and with the storage device.   
     
     
         21 . The computer program product of  claim 20 , further comprising:
 computer readable program code configured to structure the storage class memory in a log-structure; and   computer readable program code configured to mirror data in the write-through-and-back cache and in the sequential log are to avoid a need to track which data has been written to the storage device.   
     
     
         22 . (canceled) 
     
     
         23 . (canceled)