> can you guess? wrote:
> > This is a bit weird: I just wrote the following
> response to a dd-b post that now seems to have
> disappeared from the thread. Just in case that's a
> temporary aberration, I'll submit it anyway as a new
> post.
> >
>
> Strange things certainly happen here now and then.
>
> The post you're replying to is one I definitely did
> send in. Could I
> have messed up and sent it just to you, thus causing
> confusion when you
> read it, deleted it, remembered it as in the group
> rather than direct?
I used the forum's 'quote original' feature in replying and then received a
screen-full of Java errors saying that the parent post didn't exist when I
attempted to submit it.
Most of the balance of your post isn't addressed in any detail because it
carefully avoids the fundamental issues that I raised:
1. How much visible damage does a single-bit error actually do to the kind of
large photographic (e.g., RAW) file you are describing? If it trashes the rest
of the file, as you state is the case with jpeg, then you might have a point
(though you'd still have to address my second issue below), but if it results
in a virtually invisible blemish they you most certainly don't.
2. If you actually care about your data, you'd have to be a fool to entrust it
to *any* single copy, regardless of medium. And once you've got more than one
copy, then you're protected (at the cost of very minor redundancy restoration
effort in the unlikely event that any problem occurs) against the loss of any
one copy due to a minor error - the only loss of non-negligible likelihood that
ZFS protects against better than other file systems.
If you're relying upon RAID to provide the multiple copies - though this would
also arguably be foolish, if only due to the potential for trashing all the
copies simultaneously - you'd probably want to schedule occasional scrubs, just
in case you lost a disk. But using RAID as a substitute for off-line
redundancy is hardly suitable in the kind of archiving situations that you
describe - and therefore ZFS has absolutely nothing of value to offer there:
you should be using off-line copies, and occasionally checking all copies for
readability (e.g., by copying them to the null device - again, something you
could do for your on-line copy with a cron job and which you should do for your
off-line copy/copies once in a while as well.
In sum, your support of ZFS in this specific area seems very much knee-jerk in
nature rather than carefully thought out - exactly the kind of 'over-hyping'
that I pointed out in my first post in this thread.
...
> >> And yet I know many people who have lost data in
> ways
> >> that ZFS would
> >> have prevented.
> >>
> >
> > Specifics would be helpful here. How many? Can they
> reasonably be characterized as consumers (I'll remind
> you once more: *that's* the subject to which your
> comments purport to be responding)? Can the data loss
> reasonably be characterized as significant (to
> 'consumers')? Were the causes hardware problems that
> could reasonably have been avoided ('bad cables'
> might translate to 'improperly inserted, overly long,
> or severely kinked cables', for example - and such a
> poorly-constructed system will tend to have other
> problems that ZFS cannot address)?
> >
>
> "Reasonably avoided" is irrelevant; they *weren't*
> avoided.
While that observation has at least some merit, I'll observe that you jumped
directly to the last of my questions above while carefully ignoring the three
questions that preceded it.
...
> Nearly everybody I can think of who's used a computer
> for more than a
> couple of years has stories of stuff they've lost.
Of course they have - and usually in ways that ZFS would have been no help
whatsoever in mitigating.
I
> knew a lot of
> people who lost their entire hard drive at one point
> or other especially
> in the 1985-1995 timeframe.
Fine example of a situation where only redundancy can save you, and where good
old vanilla-flavored RAID (with scrubbing - but, as I noted, that's hardly
something that ZFS has any corner on) provides comparable protection to
ZFS-with-mirroring.
The people were quite
> upset by the loss;
> I'm not going to accept somebody else deciding it's
> "not significant".
I never said such situations were not significant, David: I simply observed
(and did so again above) that in virtually all of them ZFS offered no
particular advantage over more conventional means of protection.
You need to get a grip and try to understand the *specifics* of what's being
discussed here if you want to carry on a coherent discussion about it.
- bill
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