Small business backups solutions?

[Ben Scott]

On Feb 7, 2008 8:15 AM, Lloyd Kvam <python at venix.com> wrote:
>> and smart people do a full read-back-compare to
>> verify after writing
>
> Don't the DDS-4 drives (and other quality drives) automatically read and
> compare when writing.

  They do.  I just checked, and it appears even DDS has this
capability, according to the ECMA standard doc.  LTO does, according
to their website.  DLT does, according to my memory.

> I've assumed that a verification pass was only essential with single
> head drives.

  RWW (Read-While-Write) verifies that the tape drive wrote what it
was asked to write.  RWW, however, does not verify that what's on the
tape is actually a valid backup.  Hardware and media is cheap compared
to data; unless the backup window is too short, I prefer to do a full
verify, which tests just about everything, from the software to the
disks to the tape drive.

  I became aware of a bug in GNU tar this way.  If an archive member
with a "long name" was spanned across tapes, some metadata on the
second tape was written incorrectly, causing tar to fall apart when it
tried to read the data back in.  As far as the tape drive was
concerned, it had written was it was supposed to.

-- Ben