Symantec Technical Services strongly recommends that both the
Verify and
Write checksum to media options should be used for all backups that are performed. If
Verify after backup completes is not selected, a successful backup only confirms that data was written to the tape or disk; it does not verify that the tape/disk can be read or restored from the media. As long as
Write checksums to media is selected, a verify can be run at a later time. Tape verification errors can be the first indication that a tape, drive, SCSI controller, or SCSI cable are going bad. It may also be indicative of outdated or incompatible firmware on the device.
It is recommended to run the verify on all kind of backups . Tape media is much more subject to physical damage than a hard drive, so data can be written incorrectly. Simple dirt or dust can affect a tape backup too but that doesn't mean that disk are not prone to physical damage. Disk backups can have this issue but rarely
By not running a verify, data errors may not become apparent until a restore or catalog operation is attempted from tape media. For this reason, running backups without the verification and checksum options is not advised
http://support.veritas.com/docs/245177
