4 Level Reed Solomon Error Correction. VXA is the only tape drive that
employs a four-level error correction that is applied in two phases. First,
each packet includes a Reed-Solomon ECC, which can correct small
errors typically caused by noise or phase shifts. Second, when the
packets are collected in the buffer segment, they form a matrix that
employs a three-dimensional Reed-Solomon ECC (X-axis ECC, Y-axis
ECC, and Diagonal ECC).This error correction scheme can correct as
many as two lost packets in each row, two in each column, and two in
each diagonal of the buffer array. This helps VXA to achieve a bit error
rate of 1x10-17 (for example, this bit error rate is roughly equivalent to
filling a football stadium full of sand and finding a single black grain -- see
figure 3).
VXA Variable Speed Function: VXAs variable speed function enables
VXA to adjust the tape speed to match the in-coming data transfer rate of
the host. This speed adjustment enables VXA to be the first tape drive to
eliminate back-hitching and the delays and media wear associated with
it. Eliminating back-hitching also reduces wear on the drive mechanism
and the tapes which leads to greater data restore and reliability.
VXA can vary the tape speed to the rate at which the host receives or
sends data. When the hosts data transfer stops completely, VXA slows
to Ready Mode before commencing to read or write mode again. By
using Ready Mode instead of back-hitching, VXA optimizes backup and
restore job times significantly. VXAs Ready Mode has a reset time of 25
milliseconds and can be as much as 80 times faster than other tape
devices back-hitch operation, which can take anywhere up to two
seconds to complete.
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