What does backup verify do?
Say I backed up drive C: to .TIB file using bootable CD.
What does "Verify" do? Does it compare files in .TIB with original files on the disk? Or does it just verify CRC for each file within .TIB file (not very useful if you ask me)?
Validation just ensures that the archive file has not lost its integrity, it doesn't verify the fidelity to the backed up material. When the archive is built, ATI inserts checksums along the way. The validation process calculates the checksums and verifies they are equal to the ones in the file. If not, the archive file is declared corrupted. Before concluding the corruption, the user should take additional steps to make sure hardware issues or file system issues are not the source of the alleged corruption. Once the corruption is "confirmed", most likely, you wouldn't be able to restore the archive entirely. Sometimes, an archive with a proven corruption can be used to extract some files.
Validation is a very important process. We have seen in this forum archive files being corrupted inadvertently by user intervention or hardware issues. If an archive file or a chain of archive files gets validated properly, there is a high chance that it can be restored, assuming that other factors (hardware compatibility with the recovery CD, disk set up, etc.) are out of the way.
I highly recommend that each full backup be validated at least once. This can be achieved by validating any chain at least once. This ensures that at least the last full backup is validated. This is consistent with my rule of thumb that your last full validated backup should never be too old for you to go back to, if you had to.