[rescue] "I prefer a GUI"

Jeffrey Nonken jjn_rescue at nonken.net
Wed Jun 15 08:20:14 CDT 2005

On Tue, 14 Jun 2005 20:48:46 +0100, Mike Meredith wrote:
> On Tue, 14 Jun 2005 14:33:02 -0400, Jeffrey Nonken wrote:
>> At 01:44 PM 6/14/2005, you wrote:
>>> If you can't afford the $100 or so for a drive and pack(s) of
>>> tapes, you must not value your data very much...
>> And now the insults start.
> Nope. After all you've spent $100 or so for the drive and tapes.

OK, sorry. DDS panned, followed by ideas how to cheaply buy a DLT
setup, followed by this remark seemed like a rather scornful criticism
of my choices.

As a matter of fact, I spent $315 on the drive (eBay), plus more on
the backup software -- I forget how much and I'd have to find the
paper receipt, but maybe $200? Plus $40 for the SCSI controller. Many
of the tapes were free, I had access to a backup setup that was
phasing out DDS in favour of AIT. So, yeah, at least $100, maybe a bit
more. :)

> DDS is fine for light-weight duty on a home network. Some of us
> used them for more heavy-duty work, and have had *bad* experiences
> with the tapes and drives. We've still got a couple of hundred DDS
> tapes at work in the computer room, and I can't walk past without a
> little shudder at the memories.
> At one time, when I was on the 'tape monkey' duty, I would carry 10-
> 15Kg of DDS tapes on a daily basis to a fire safe. That level of
> tape use is going to result in problems especially when you can
> wake up in a cold sweat in the middle of the night at the thought
> of restoring a server from DDS tapes that have been used a little
> too often.

I found a dirty little secret while I was doing client backups at my
job. I smoked the heads on an HP DDS-3 tape autochanger after six
months of use and called their tech support. After concluding that the
drive really wasn't working, he asked how many hours/night I'd been
using it? I said, about 14. He said, that's way too much! You can't
use it for more than 3 hours a night, the heads have a 12% duty cycle.
I confessed I'd not known that. After a few minutes of setting up an
RMA I asked if he could tell me where to find that information in the
manual, because I'd missed that and really wanted to know. After a
slight hesitation he confessed that it wasn't IN the manual.

Ah hmm.

I got warrantee service on that drive, of course.

It's not just a matter of wear; exceed the duty cycle and the heads
overheat, which causes the metal to soften, which causes
disproportionate wear.

Anyway. The Sony drive supposedly has a 20% duty cycle, and it's a
better drive, but we're still talking about 5 hours/night. Less than
two tapes.

So I've fiddled with my schedules to keep it that way, and if I forget
to change tapes partway through I end up with one full tape and heads
that haven't been pushed to their limits. Not a bad thing.

I've had this Sony drive for almost 5 years now (bought used, of
course) and it's got its problems, but data-integrity-wise it's been
trucking right along, even on some pretty old tapes. On some tapes it
retries a fair amount, but it's been making it through in the end. And
yes, I've done enough restores to be pretty confident that if it can
succeed on the write, it'll succeed on the read.

One of the nice things about DDS is that it does a read-after-write on
the fly and will detect a write error instantly. I don't bother with a
separate verify because it's never, ever been needed and all it does
is give me false errors when the file it's comparing to has been
changed since the backup, not to mention taking more time and causing
more wear.

Except when the heads have been too worn. I've seen drives eventually
succeed on the write and then fail on the read-back later, but that's
been on drives that have been abused and their heads too far gone to
work reliably.

I have to wonder: How much of DDS's piss-poor reputation has been
because of this duty cycle that none of the manufacturers seem to want
to admit to? At least, not for any of the drives I've worked with
(Wangdat, HP, and Sony).

BTW, I'm planning to phase out this DDS eventually, and being on a
budget I'm trying to avoid buying more tapes that I'm just going to
stop using, but meantime it's the system I've got. If somebody had
access to a bunch of free used DDS-3 tapes that could be cut loose I'd
be willing to pay shipping. (No, I don't really want DDS-2 or DDS-1.
Already got some.)


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