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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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