referring to fig4 for a method for processing cache data in a redundant server system , the system includes a console end 3 and a redundant control end 4 . the console end 3 has a cache memory 30 for storing cache data , and the redundant control end 4 has another cache memory 40 , and the console end 3 uses a mirroring mechanism to process and convert the cache data into a mirrored cache data as shown in fig5 , such that if the console end 3 needs to send the mirrored cache data to the redundant control end 4 through a transmission unit 5 and save the mirrored cache data in the other cache memory 40 , the console end 3 and the redundant control end 4 will carry out the following steps : step ( 1 ): the console end 3 creates a data structure information based on the mirrored cache data , and the data structure information comprises a transmission record , and the content of the transmission record includes a number of times that the console end 3 sends the mirrored cache data to the redundant control end 4 and cannot save the mirrored cache data in the other cache memory 40 . step ( 2 ): the data structure information is queued at the console end 3 . step ( 3 ): the console end 3 sends the mirrored cache data to the redundant control end 4 through the transmission unit 5 and processes other following mirrored cache data and wait for a reply from the redundant control end 4 . step ( 4 ): if the redundant control end 4 receives the mirrored cache data , then a storage space of the other cache memory 40 will be determined whether or not it is sufficient to save the mirrored cache data . the redundant control end 4 adds the capacity of the currently saved data of the other cache memory 40 and the capacity of the mirrored cache data to obtain a comparing data capacity , and then compares the maximum data capacity of the cache memory 40 with the size of the data capacity to determine whether or not the storage space of the other cache memory 40 is sufficient to save the mirrored cache data . if the maximum data capacity of the other cache memory 40 is greater than the comparing data capacity , then go to step ( 5 ), or else go to step ( 7 ). step ( 5 ): the redundant control end 4 saves the mirrored cache data into the other cache memory 40 and issues an already - saved message to the control end 3 to indicate that the redundant control end 4 has saved the mirrored cache data . step ( 6 ): the console end 3 receives the already - saved message , and then delete the data structure information of the corresponding mirrored cache data in the queue , and then ends the procedure . step ( 7 ): if the redundant control end 4 cannot save the mirrored cache data to the other cache memory 40 , then the redundant control end 4 will reply a notice message to the console end 3 ; step ( 8 ): if the console end 3 receives the notice message , then the console end 3 will increment the number of transmissions by one for the transmission record ; step ( 9 ): the console end 3 determines whether or not the number of transmissions recorded in the transmission record exceeds a predetermined maximum number of transmissions of the console end 3 . if the console end 3 determines that the number of transmissions recorded in the transmission record has exceeded the maximum number of transmissions , then go to step ( 10 ), or else go to step ( 3 ); step ( 10 ): the console end 3 flushes the cache data directly into a hard disk 32 at the console end 3 , and then ends the procedure . referring to fig4 for the status that the other cache memory 40 cannot save the mirrored cache data , the first record of cache data a and second record of cache data b saved in the cache memory 30 are processed and converted into a first record of mirrored cache data a ′ and a second record of mirrored cache data b ′ respectively and saved into the other cache memory 40 according to the aforementioned procedure of the present invention . after the third record of cache data c saved in the cache memory 30 is mirrored into a third record of mirrored cache data c ′, the redundant control end 4 determines that the storage space of the other cache memory 40 is insufficient to save the third record of mirrored cache data c ′ ( as indicated by the dotted line in fig4 ), and then the console end 3 will flush the third record of cache data c into the hard disk 32 to avoid a loss of cache data . in the present invention , the data structure information further includes a cache data identification header and a content index , and the cache data identification header further includes a device identity data , a block address and a data length of the cache data , etc , wherein the device identity data is a serial number of the hard disk containing the cache data , and the block address is a block address of the hard disk containing the cache data , and the content index is a storing address of the cache memory 30 for storing the cache data . if the console end 3 determines that the number of transmissions recorded in the transmission record has exceeded the maximum number of transmissions , the console end 3 will read the storing address of the cache memory 30 corresponding to content index based on the content index to obtain the cache data , and then the console end 3 flushes the cache data into a block address of the hard disk corresponding to the cache data identification header according to the cache data identification header . in summation of the description above , the following three mechanisms are provided , if the console end 3 cannot save the mirrored cache data into the other cache memory 40 : 1 . the console end 3 can resend the mirrored cache data ; 2 . the console end 3 has a limitation of a maximum number of transmissions for resending the mirrored cache data ; and 3 . the console end 3 will flush the cache data into the hard disk 32 if the mirrored cache data cannot be resent . further , the following three mechanisms are provided , if the redundant control end 4 receives the mirrored cache data : 1 . the redundant control end 4 can determine the capacity for storing the other cache memory 40 ; 2 . the redundant control end 4 determines whether or not the mirrored cache data can be saved in the other cache memory 40 ; 3 . if the redundant control end 4 saves the mirrored cache data into the other cache memory 40 , the redundant control end 4 replies an already - saved message to the console end 3 . if the mirrored cache data is saved in the other cache memory 40 , the notice message will be replied to the console end 3 . the present invention has been shown and described in detail , various modifications and improvements thereof will become readily apparent to those skilled in the art . accordingly , the spirit and scope of the present invention is to be construed broadly and limited only by the appended claims and not by the foregoing specification .