Hitachi G1000 User Manual page 11

You can configure Volume Shredder to overwrite data from three to eight
times, and each time the system overwrites the data you can configure the
dummy data to be any hexadecimal number from 0 to FFFF.
After the system finishes overwriting data, you can view the results in the
user interface or, if configured, you can open the compressed results files.
We recommend that you execute the shredding function at times of day
when the host I/O load is lowest. If the number of LDEVs to be shredded is
large, shredding operations might affect host I/O operations. Use the
following formula to determine the standard required time for a shredding
operation.
(time required for shredding) = (time required for one dummy data
write (standard required time)) x (number of times dummy data is
written (n))
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Overview of Hitachi Volume Shredder
Hitachi Virtual Storage Platform G1000 Hitachi Volume Shredder User Guide