How about setting up a white board / aka NetMeeting !
I think this thread has gone on for some time now, and yet there still
appears to be 2 different opinions.
Not going to please everyone.....! :-) personally, I would not be worried
about it and will just step out of the debate and move on.
Right or wrong, I really don't care that much :-)
But anyhow, something like DIGG Whiteboard might help - think its still free
if those wishing to continue the debate want to continue offline :-)
Bye !
Regards
Simon Weaver
3rd Line Technical Support
Windows Domain Administrator
EADS Astrium Limited, B23AA IM (DCS)
Anchorage Road, Portsmouth, PO3 5PU
Email: Simon.Weaver AT Astrium.eads DOT net
-----Original Message-----
From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of Curtis
Preston
Sent: Friday, October 19, 2007 8:38 AM
To: bob944 AT attglobal DOT net; veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] Tapeless backup environments?
I wish we had a white board and could sit in front of each other to finish
the discussion, but it's obvious that it's not going to be resolved here.
You believe I'm missing your point, and I believe you're missing my point.
>what matters is if you use a shorthand to track the
>values which can't tell that Feb 7 and Dec 28 are different values
>because you put them in the same hash bucket and therefore think that
>everything that bucket is Feb 7, you retrieve the wrong data.
Not sure how many times I (or others) have to keep saying, the dates are not
the data that are being deduped. The dates are the hashes. The data is the
person.
>An 8KB chunk of data can have 2^65536 possible values. Representing
>that 8KB of data in 160 bits means that each of the 2^160 possible
>checksum/hash/fingerprint values MUST represent, on average, 2^65376
>*different* 8KB chunks of data.
This, again, only makes sense if you are using the hash to store/reconstruct
the data, not to ID the data. The fingerprint (like a real fingerprint) is
not used to reconstruct a block, it's only used to give it a unique ID that
distinguishes it from other blocks. You still have to store the block with
the key. And with 2^160 different fingerprints, that means we can calculate
unique fingerprints for 2^160 blocks. That means we can calculate a unique
fingerprint for
1,461,501,637,330,900,000,000,000,000,000,000,000,000,000,000,000
blocks, which is
11,832,317,255,831,000,000,000,000,000,000,000,000,000,000,000,000,000
bytes of data. That's a lot of stinking data.
>If that doesn't concern you, well, it's safe to say I won't be hiring
>you as my backup admin. Or as my technology consultant, since you
I really don't think you need to make it personal, and suggest that I don't
know what I'm doing simply because we have been unable to successfully
communicate to each other in this medium. This medium can be a very
difficult one to communicate such a difficult subject in. I think things
would be very different in person with a whiteboard.
>should know from earlier postings that spoofing your favorite 160-bit
>hashing algorithm with reasonable-looking fake data is now old hat.
>The exploit itself should concern us, not to mention that it also
>illustrates that similar data which yields the same hash is not the
>once-in-the-lifetime-of-the-universe oddity you portray.
They worked really hard to figure out how to take one block that calculates
to a particular hash and create another block that calculates to the same
hash. It's used to fake a signature. I get it. I just don't see how or
why somebody would use this to do I don't know what with my backups. And if
we were having this discussion over a few drinks we could try to come up
with some ideas. Right now, I'm as tired as you are of this discussion.
>Everything mentioned here was covered in the original postings a month
>ago. Unless there's something new, I'm done with this.
You're right. IN THIS MEDIUM, you don't understand me, and I don't
understand you. Let's agree to disagree and move on.
For anyone who's still reading, I just want to say this:
I was only trying to bring some sanity to what I felt was an undue amount of
FUD against the hash-only products. I'm not necessarily trying to talk
anyone into them. I just want you to understand what I THINK the real odds
are. If after understanding how it works and what the odds are, you're
still uncomfortable, don't dismiss dedupe. Just consider a non-hash-based
de-dupe product.
Curtis out.
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