For example: if I use tar to write on LTO-1 tape (200/100 gb) and during the backup tar hits the end of tape. Will I be able to restore such a corrupted archive? How to solve the possible problem? How to determine how much can the tape store with hardware compression?
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Tar will simply append one file after another, as it was named for being a "Tape ARchiver", and you should be able to recover complete files up to the point where you ran out of tape. You would simply "un-tar" the files until you reach the end of the tape, and then discard the final file restored.
It is impossible to know how compressible your data is without actually compressing it first. Compression depends entirely on the data being compressed and is not a fixed value. You cannot guarantee fitting 250GB on a 100/200GB tape unless you know for a fact that you have a large amount of repeated data.
It is entirely possible that for a "normal" system backup that you could get that kind of compression as executables tend to have a lot of redundant and compressible data, but you cannot say for 100% certain. As a result you will have to find out how much space your backup requires by trial and error, you should not be aiming to 100% fill your first tape but instead assume that the compression will give you some unknown margin for safety.
Mokubai
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