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    Subjectlarry, nat - go away(or go private)
    btw nat, bk's integrity checking will help ensure your backups are useful
    for more than just dumpster bait.


    Eric van Tassell
    Texel Software, Inc. - System Software Engineering for Windows/NT
    277 Cochran Hill Rd. Voice : 603-487-5006
    New Boston, NH 03070 USA Fax : 603-487-5166
    email :

    > -----Original Message-----
    > From:
    > []On Behalf Of Larry McVoy
    > Sent: Tuesday, September 28, 1999 2:38 AM
    > To:
    > Subject: Re: [ OFFTOPIC ] Re: The Linux Kernel Project Management System
    > On Tue, Sep 28, 1999 at 01:50:25AM -0400, Nat Lanza wrote:
    > > You don't listen, do you? No matter how much I say "application-level
    > > checking is good but you still need other measures", all you hear is
    > > "application-level checking is bad".
    > Sure I do and I heard you and Peter the first time. And I've been
    > in this argument a hundred times in a hundred different disciplines.
    > If you had read Clark's paper (don't they make people read that in OS
    > 101 anymore?), you'd realize that what you are saying is like this:
    > if I'm going from point A to point Z through B, C, D, E ...
    > then if each link is safe, then the whole way is safe. I.e.,
    > if A<->B doesn't screw it up, and B<->C doesn't screw it up,
    > etc., then it follows that A<->Z doesn't screw it up.
    > And I am saying that's wrong (which is point of Dave's paper).
    > You have to do end to end checking, you can't do intermediate checking,
    > that can't be guarenteed to be safe. This is networking 101 and it is
    > also systems architecture 101 - any hardware class should teach you this.
    > You keep telling me that backups and mirroring etc are needed and what
    > you are missing is that the things doing the backups and mirroring
    > have no way of knowing if that which they are storing is good or bad.
    > > > In 10 or more messages you've failed to get the point. Doing
    > backups of
    > > > bad data is not very useful. How the hell do you know that
    > you need to
    > > > restore from tape if the system never tells you that anything
    > is wrong?
    > > > RCS / CVS store the latest version in clear text - every
    > earlier version
    > > > could be completely corrupted and you'll cluelessly (through
    > no fault of
    > > > your own) be backing up, mirroring, raiding, and CDROM
    > burning COMPLETE
    > > > AND UTTER GARBAGE. Which you won't find out until you need to get an
    > > > _OLD_ version to fix a bug.
    > >
    > > Yeah, it's possible. But now we've moved from "totally screwed" to
    > > "way inconvenienced because I have to play hunt-for-the-tape for a
    > > long time". No, it's not optimal. I'm not claiming it is. I'm simply
    > > claiming that it's possible to avoid being screwed without having your
    > > version control system do lots of fancy error checking.
    > How? The only way I know of is to save infinite backups to the
    > beginning of time and go through them all one at a time. Let's see,
    > you were complaining about the cost of the product. Let's suppose you
    > have to do this once in the lifetime of your project and it is under
    > extreme pressure because the NSA needs a bug fix right now to a 5 year
    > old version of your code and you can't reproduce that 5 year old version
    > because your repository was corrupted. Now you have a couple hundred
    > backup tapes to look through to find this.
    > At this point, should this have happened, exactly how much would you
    > pay to get rid of the problem? And how hard would you be cursing the
    > guy that thought backups were a reasonable answer?
    > > Question: Does BitKeeper prevent me from having garbage in my
    > > repository? Completely? Or does it just make it less likely? I believe
    > > it just makes it less likely, which is why I claim that backups and
    > > disk arrays are still more important.
    > BK gives you back what you gave it. Period. BK checksums the file
    > every time you do any operation on it. You do a checkin, checkout, diff,
    > whatever, it checksums the entire file. It's a pretty shitty checksum,
    > but none the less, it checksums it. It also checksums each version of
    > each file; these checksums are passed in patches and checked when the
    > revision history is sent.
    > In addition, BK is inherently distributed with each repository having
    > copies of the revision history. So when a file goes bad, the likelihood
    > of you being able to get a good copy from some other repository is
    > extremely high.
    > BK can't prevent garbage in. I don't claim it does. What I claim is
    > that BK tries hard to make sure it can reproduce your world as of any
    > point in time. If you checked in garbage, you get back THE SAME GARBAGE,
    > not different garbage.
    > > You claimed that Aegis was worse than BK because of support.
    > I did no such thing. I pointed out that Aegis has some problems and
    > there is no plausible long term remedy to those problems. The point
    > was that the free software model, for these sorts of systems, has had
    > years and years to prove that it works and it has failed miserably.
    > This stuff just isn't sexy enough for people to work on it for free and
    > really solve all the problems. You can argue all you want but they are
    > hollow arguments - Aegis has been here for 7 or 8 years, CVS for longer,
    > and yet people feel the problem still isn't solved.
    > That's not a support issue, that's a business model issue.
    > > don't care about what anyone who disagrees with you has to
    > > say. They're all either fools or amateurs or deluded or in some way or
    > > another idiots who should not be listened to. Only you have the
    > > answer, and it is BitKeeper. You made it so the Linux kernel could use
    > > it and love it, and by God we'd better all be grateful. You deserve
    > > more than the insolence of dissenting opinions, you deserve
    > > applause.
    > Nat, I've shipped a lot of commercial code. Mostly in I/O and
    > file systems. I've spent an enormous amount of effort trying to make
    > sure that the system doesn't screw up the customers data. I take data
    > integrity seriously, perhaps because I've worked at places like SGI where
    > performance mattered more than integrity (the same line of reasoning
    > which gets RCS into trouble). I've done tons of customer visits where
    > I got to listen to frustrated customers scream at me for bad decisions
    > that other people made, decisions which ended up in corrupt data.
    > All that left me with a healthy respect for user data. And, yes, I think
    > people that don't take that seriously are very deluded and have absolutely
    > no business in the source management area (and I'd like to get them out
    > of operating systems in general, perhaps NFS would actually work then).
    > Sometimes I think that I'm not yet worried enough about integrity and
    > it makes my skin crawl to hear other people blithely dismiss it with
    > statements like "that's what backups are for".
    > I'm sorry if you feel unheard, or beat up, or whatever. I'm not attacking
    > you personally, I don't even know you. I'm attacking what sad experience
    > has taught me are misguided principles. There's a difference. You are
    > very likely an extremely sharp guy, most opinionated people are. But you
    > are also saying some things which I know to be incorrect. I'm attacking
    > those statements, not you.
    > --
    > ---
    > Larry McVoy
    > -
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