Rodrigo Barbosa wrote:
>
> On Thu, Mar 29, 2007 at 04:31:45AM -0000, Mark Schoonover wrote:
>> If you rely solely on your tape software verification to tell you your tapes
>> are 100%, there will come a day, you'll be in for a surprise. The only 100%
>> sure fire way to determine if your tapes are good is to actually restore
>> from them back to a drive, and open them with the applications that created
>> those files. Only after that kind of testing, can you be sure your tapes are
>> good. I've had many tapes verified from the days of Arcserve, through
>> Brightstor, Arkeia, CTAR and BRU. All of these backup software systems ran,
>> and verified flawlessly, then a disaster struck only to find out my verified
>> tapes actually had problems with them.
>
> And how is that any different than any other media, including disks ?
An online backup system that uses rsync with the --ignore-times option
(as, for example backuppc during full runs), will be reading your
existing files frequently and re-copying any mismatches detected with
the rsync algorithm. Also, the system may offer the option to archive
to some other media at convenient times which gives you another chance
at it. A problem I've seen with older tape drives was that the heads
would lose alignment so that that tapes would only work in the drive
that wrote them. You might verify a tape and send it offsite only to
find after a disaster that another drive would not read it. I don't
know if newer designs have eliminated this problem or not. If not, you
really need a 2nd drive to do the verify/read test.
--
Les Mikesell
lesmikesell at gmail.com