Check for Media Errors

Check for media errors by:

• Reading from the Media
• Writing to the Media

Reading from the Media

Reading from the media involves detecting the data and format information on a media.

• You can use the dd command to check a disk or diskette.

  For example, to read a diskette on drive rfd0, enter:

  dd if=/dev/rfd0 of=/dev/null bs36b

  where the bs flag specifies the internal buffer size for dd.

  Note: A value of 36b for this flag greatly enhances the performance of this operation. With a buffer size of 18KB, dd can read both tracks of a diskette in only two revolutions of the diskette.

• You can also use the tcopy command to read a tape.

  For example, to read a tape on device rmt0, enter:

  tcopy /dev/rmt0

• Media errors are also recorded in the error log. For example, entries labeled TAPE_ERR1 indicate tape media error. For further information, see "Error Logging Facility" and "Error Identifiers for the Error Log" .

  If the media can be read successfully with the dd or the tcopy command, a syntax or usage problem possibly exists. Syntax or usage problems could include:

• Incorrect archive utility was used.
• cpio backup was not written with ASCII headers and the command specifies ASCII headers (-c).
• tar command has calculated a checksum different from what is recorded on the tape indicating that the incorrect volume may be in the drive. (Use the -i flag to ignore checksums.)
• For tapes, the DEVICE block size is different than the size of the tape file's blocks.
• For tapes, the archive utility does not have enough buffer space to hold an entire block from the tape file.

Writing to the Media

Attention: The reformatting procedure destroys all data on the media.

Writing to the media also helps you check for media problems.

• Use the format or dosformat (formats a DOS diskette) commands to format diskettes.

  For example, to format a diskette in the diskette drive rfd0, enter:

  format -d /dev/rfd0

  OR

  dosformat -D /dev/rdf0

• Use the dd command to write data to a tape.

  For example, to write the file motd to the device rmt0, enter:

  dd if=/etc/motd of=/dev/rmt0

  Note: Writing data to a tape ensures that only that portion of the tape that is written to is not damaged.