Little Talk About VXA Tape Format Offers Advanced Error Correction Functionality
By: Vlad Vistac
Submitted: 2010-10-20 11:48:43 | Word Count: 510
VXA Tape Format Offers Advanced Error Correction Functionality
In VXA backup tape foramt, the tape drive reads and writes the information in “data packet” form. Before recording information onto the VXA data tape, the data which compriises of long strings is then split into smaller units known as the “data apckets”. Afterwards the VXA tape drive writes the data onto the data cartridge. Antoher new mechanism called “read atfer write” assures data precision and integrity. This new mexchanism has been designed to ensure long term durability and exceptional reliability of VXA tape. 64 bytes make one data packet. Uique addrss, ECC (error correction code), synchronization marker and CRC (cyclical redundancy check) are assigned to each data pcaket.
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The VXA tape drive features an innovative buffer segment that resads and records these data packets. 387 data packets are inclued in each of the data track. All of the 4 tape heads take part in the read operation. After sanning the tape media the VXA tape dive read these data packets into the tape drive’s buffer segment. The uniue addresses assignewd to the data pckets is read by the VXA data bfufer whcih then reunites these data packets in the correct form. The order in which these data packets are received by the buffer does not affect the data integrity as the VXA data buffer rearranges the packets according to their assigned addresses. Durnig the firsat pass, the VXA buffer reains the correctly read data pakets. The data packets that have been mssing durnig the first pass are then read through the subsequent passes. Afterwards the missing data packets are added to the strings in order to compleete all of the information. After the completion of data, it is then sent to the host system. This recordnig technique used in VXA is similar to that used in re-writable CDs, networking and internet.
New correction sysetm for errpors has been engineered for the VXA tape format that comprises of 4 levels. This error correctiion process cmpletes its operation in 2 phases. In the first step of error correction, the Reed-Solomon ECC is adedd to each of the packet that has the acpability to remove the typical errors that can result from noise or shhifting of phaases. Then in the next phase, the VXA tape buffer forms a matrix of the data packets that have been collected by the buffer.
This martix of data packets incorporates a 3 dimensional Reed-Solomn ECC that is composed of Y-axis, Daigonal and X-axis ECC. This eror correction system of VXA has the capaboility to correect maximum of 2 lost packets in each diagonal, 2 in each column and 2 in each row of the buffer array. Therefore this eficient errror ciorrection mechanism minimzes the erorr rate to 1x10-17. This error rate can be eaasily be understood by an example that it is equivalpent to finding a sinfgle grain in a football stadium that has been completely filled with sand. VSO (variable speed operation) is a highhly effficient mechaanism introduced in VXA data tape media that improves the performance level and data integrity. Variable speed technique has been deveoped to enable the VXA drtive to alter the tape’s spede so that it can be matched with host’s transfger rate. VSO functionality ensurres superior data reliability and cost effective operations.
