On Mon, 11 Aug 2008 11:42:55 -0700, Newton, Ernie <[log in to unmask]> wrote:

> Greetings,
>
> We've been having backup troubles and the DAT drive blames the tape and the
> tape blames the DAT drive.  It's almost like they're married.
>
> When a store process encounters a "bad media" does it write information on
> the tape?  I've heard that there is a "history" written to the tape.
>
> Fact or fiction?
>
> If it's fact, is there a way to read this data?
>

I don't know whether or not STORE itself writes anything to the tape, but it
is my understanding that various error counts and other information is
written to the tape by the tape drive itself.

Once upon a time I learned that tapes have a usage count recorded on them
and I did some research on where that data is stored and how to access it. 
The usage count and error counts, etc., seem to be stored on the tape in
what SCSI calls "LOG PAGES".  I think they're written to the tape when it is
ejected.  The data can be accessed by a program using the SCSI LOG SENSE
command.

On the HP3000, CSTM can be used to access the LOG SENSE data but I'm pretty
sure that functionality is password protected.  If you have DAT drives on
another system, I seem to recall also seeing some programs that ran on
FreeBSD or Solaris that could read the data.

However, according to this post from many moons ago, it looks like some of
the data you want might already be in the MPE/iX logs:

(http://groups.google.com/group/comp.sys.hp.mpe/msg/961f844735b2a8ff?hl=en
or http://raven.utc.edu/cgi-bin/WA.EXE?A2=ind9507C&L=HP3000-L&amp;T=0&F=&S=&P=11705)

> From: [log in to unmask] (Larry Nichoalds)
> Subject: Re: How may times can dds tapes be used
> Date: 1995/07/19
> Message-ID: #1/1
> sender: news@hpax (News Admin)
> organization: Hewlett-Packard
> newsgroups: comp.sys.hp.mpe
>
>
> It may be of value for you to know that with the 5.0 release of MPE there
> is a new log record with documents the effort that the DDS drive expended
> when either reading or writing the tape.  The records can be accessed by
> using the logtool utility and the data the contained in the record can
> tell you the following:
>
>    Current number of groups written
>    Current RAW (Read after Write) retries
>    Current number of groups read
>    Current number of ECC3 retries
>    Whether the clean-me bit is on
>
> The RAW count will give an indication as the how hard it was to put data
> on the tape, while the ECC3 retries indicate the effort required to get the
> data from the tape.  High counts in either of these field would indicate
> the potential need to replace the tape. 
>
> As mentioned by the other responses being conscientious about cleaning can
> have signifcant returns, but if your interested in monitoring the 
> specific tape performances you can get the information from the log.
>
> The log record is, by the way, recorded everytime a tape is closed.

According to my notes, the LOGTOOL command would be something like this:

    LIST LOG=### ;TYPE=111 ;LDEV=7


Hope that helps.

Edward Berner
Yosemite Community College District

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