[Info-vax] TK50 - this is annoying...

[Rich Jordan]

On Oct 10, 3:00 am, urbancamo <m... at wickensonline.co.uk> wrote:
> On Tuesday, 9 October 2012 15:03:06 UTC+1, Stephen Hoffman  wrote:
> > On 2012-10-09 10:08:09 +0000, Johnny Billquist said:
>
> > > On 2012-10-09 03:59, Paul Sture wrote:
>
> > >> Shudders at the thought of relying on DDS-3 for all backups.
>
> > >> BTDT. Got bitten. :-(
>
> > > :-)
>
> > Yeah.  Bad Idea.
>
> > > I regularly verify them, and so far no problems. But I have seen a
>
> > > large number of failed drives at places...
>
> > The head-pass count rating on the DDS media makes it nearly write-once
>
> > read-maybe media, particularly around the tape headers.  (IIRC, 2000
>
> > passes.)
>
> > There's a reason that DDS media and DDS gear is cheap, after all.
>
> > That head-pass rating wasn't far off of empirical, either.  I got maybe
>
> > a week's worth of use out of each cartridge.
>
> > That was using the cleaning cartridge at the recommended intervals.
>
> > Verifying?  That's just scraping off a little more of that precious oxide.
>
> > Count up a tape mount and multiple BACKUP and MOUNT-DISMOUNT sequence
>
> > sometime.  Add in verifying, if you're inclined.  You can visit the
>
> > tape heads a number of times with a multi-disk backup to a single DDS,
>
> > if you're not really careful about how you handing the mounting and
>
> > dismounting and BACKUP commands in your DCL.  Pretty soon, you're close
>
> > to the head-pass rating (assuming that rating even matches la realidad)
>
> > and off slides your data.
>
> > I scrounged and switched to DLT an aeon ago, and never looked back.
>
> > DLT, SDLT and LTO are vastly more reliable, barring your having
>
> > acquired an average box of crap-grade recording media.  (There's a fair
>
> > amount of that around, too; counterfeit or just generic-brand dreck.)
>
> > Even the fossil-grade TK50, if you have "current" firmware and one of
>
> > the second-generation hammerheads, was more reliable than DDS.
>
> > Nowadays, scrounging a decently-less-than-ancient SDLT or LTO is
>
> > trivial.
>
> > Cue my usual "upgrade" discussion.
>
> > --
>
> > Pure Personal Opinion | HoffmanLabs LLC
>
> Just to add my 2 cents. Firstly, I don't disagree with anything said. I don't rely on DDS any more is healthy.
>
> However, on a slightly different tack data longevity is perhaps less of an issue. I have read several DDS1/DDS2 tapes recently that were written in 1994 without any issues.
>
> My usage pattern for DDS is typically to only use an individual tape a few dozen times, so maybe that pattern has saved me from disaster.
>
> Mark.

We purged a set of very old backups last time we moved; TK50 and DDS1
DAT from 1990-1993 (thought they were long gone and found them in a
box when we were packing).  For grins I tried to read them on the one
remaining TLZ07 and TZ30 drive.

I was able to read about 60% if the DAT's without error, and another
20% with recoverable errors; the remaining 20% were only partially
recoverable.  None were totally unreadable.

The TK50s were much more problematic; less than half were readable at
all.  Some would just spin in the drive for a while then unload.  This
TZ30 at the time was able to init, write, verify, and read tapes
(though it could have been out of spec so unable to read other drive's
tapes, a situation we saw with DAT drives too).