Check out eMag's indepth guide on tape technology where you'll learn about the factors that can slow or prevent restoration/recovery. 

For instance, did you know that 99% of backup software will write and/or read data up to an error point and then fail? This is desirable when writing data, but when reading data, it prevents access to other data in non-error areas on the tape. Most enterprise software solutions will write to a tape until an error is found. Once an error is detected, the system will write protect the tape and continue onto another tape.

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