High-speed snapshot method

Abstract

When a snapshot of data is taken, it is after a write request comes from the host equipment that old data on the source-side magnetic disk to the snapshot-side magnetic disk; therefore, it takes a long time before new data is actually written in the source-side magnetic disk. To overcome this problem, by analyzing data update information, and from a result of analysis, by deciding an area that has high possibility of receiving a request to write data, and having data of that area previously copied to the snapshot-side magnetic disk, it is possible to take a snapshot very quickly.

1 . A method for speeding up a snapshot operation in a computer system wherein a host equipment is connected through a switch to a source-side magnetic disk and a snapshot-side magnetic disk, said method comprising the steps of: 
 detecting data in an area where data is highly likely to be written next; and    previously copying said data in said snapshot-side magnetic disk.    
     
     
         2 . A method for speeding up a snapshot operation in a computer system wherein a host equipment is connected through a switch to a source-side magnetic disk and a snapshot-side magnetic disk, said method further comprising the steps of: 
 detecting data in an area where data is likely to be written with a possibility higher than a predetermined value; and    copying said data in memory.    
     
     
         3 . A snapshot controller for, in response to a request to write data into said source-side magnetic disk from a host equipment, copying a content in an area of said source-side magnetic disk at a point in time to a corresponding area in a snapshot-side magnetic disk, said content being overwritten by new data after said point in time, said snapshot controller comprising: 
 a magnetic disk read/write executing unit for reading/writing data by a request from said host equipment;    a write-ahead/read-ahead executing unit for writing ahead/reading ahead data in said source-side magnetic disk;    a memory controller for reading and writing necessary information; and    a memory for storing said information.    
     
     
         4 . A snapshot controller in  claim 3 , wherein said memory comprises a magnetic disk information table; a write-ahead information table; a read-ahead information table; and a data update information table.  
     
     
         5 . A snapshot controller in  claim 4 , wherein said magnetic disk information table includes host equipment information showing which host equipment sent a read/write request; magnetic disk pair information showing a pair of magnetic disks where a snapshot operation is performed; area information showing how many sectors of data are read ahead/written ahead in which areas; and read/write information showing whether data is read or written.  
     
     
         6 . A snapshot controller in  claim 4 , wherein said write-ahead information table includes source-side magnetic disk number information showing data of which magnetic disk is written ahead; and data write-ahead area information showing how many sectors of data are of which areas are written ahead.  
     
     
         7 . A snapshot controller in  claim 4 , wherein said read-ahead information table includes source-side magnetic disk number information showing data of which magnetic disks is read ahead; data read-ahead area information showing how many sectors of data of which areas are read ahead; and read-ahead data showing data read ahead.  
     
     
         8 . A method for controller in  claim 4 , wherein said data update information table includes host equipment number information showing from which host equipment a write request came; source-side magnetic disk number information showing the magnetic disks new data was written; and data write area information showing the areas where new data was written and how many sectors of data were written.  
     
     
         9 . A snapshot controller in  claim 3 , wherein said magnetic disk read/write executing unit comprises means for obtaining information about the areas where data was written ahead in the snapshot-side magnetic disk; and means for deciding the write-ahead/read-ahead state to see if the area the host equipment is making a data write request coincides with the area where data was written ahead or read ahead.  
     
     
         10 . In the snapshot controller in  claim 4 , wherein said write-ahead/read-ahead executing unit comprises means for deciding if read-ahead data is stored in said read-ahead information table; means for, when read-ahead data is stored in the read-ahead information table, copying read-ahead data to the snapshot-side magnetic disk; and means for recording the area data of which was copied as the write-ahead area in said write-ahead information table.  
     
     
         11 . A snapshot controller in  claim 4 , wherein said write-ahead/read-ahead executing unit comprises means for obtaining log information about writing data to the source-side magnetic disk, from said data update information table; means for analyzing obtained information and deciding a write-ahead area and data capacity for writing ahead; and means for writing ahead data in a decided write-ahead area to said snapshot-side magnetic disk.  
     
     
         12 . A snapshot controller in  claim 4 , wherein said write-ahead/read-ahead executing unit comprises means for obtaining log information about writing data to said source-side magnetic disk from said data update information table; means for analyzing obtained information and deciding a read-ahead area and data capacity for reading ahead; and means for storing data in a decided read-ahead area in said read-ahead information table.  
     
     
         13 . A host equipment for, by issuing a request to write data into said source-side magnetic disk, copying a content in an area of said source-side magnetic disk at a point in time to a corresponding area in a snapshot-side magnetic disk, said content being overwritten by new data after said point in time, said host equipment comprising: 
 magnetic disk read/write executing unit for reading/writing data according to said data read/write request;    a memory controller for reading and writing necessary information from a memory; and    a memory for storing necessary information.    
     
     
         14 . A switch for, in response to host equipment's request to write data to a source-side magnetic disk, copying a content in an area of said source-side magnetic disk at a point in time to a corresponding area in a snapshot-side magnetic disk, said content being overwritten by new data after said point in time, said switch comprising: 
 a magnetic disk read/write executing unit for reading/writing data according to the request from said host equipment;    a write-ahead/read-ahead executing unit for writing/reading data according to the request of said host equipment;    a memory controller for reading and writing necessary information from a memory; and    a memory for storing necessary information.    
     
     
         15 . A storage system for, in response to host equipment's request to write data to a source-side magnetic disk, copying a content in an area of said source-side magnetic disk at a point in time to a corresponding area in a snapshot-side magnetic disk, said content being overwritten by new data after said point in time, said storage system comprising: 
 a write-ahead/read-ahead executing unit for writing/reading data according to the request of said host equipment;    a memory controller for reading and writing necessary information from a memory; and    a memory for storing necessary information.    
     
     
         16 . A snapshot controller comprises: 
 means for discriminating between an area from which data was copied by a data write request from host equipment and an area from which data was copied by a write-ahead operation by using two kinds of flags when old data in the source-side magnetic disk was copied to the snapshot-side magnetic disk.