[e2e] Re: [Tsvwg] Really End-to-end or CRC vs everything else?
vjs at calcite.rhyolite.com
Mon Jun 11 19:39:11 PDT 2001
> From: Jonathan Stone <jonathan at DSG.Stanford.EDU>
> Yes, there are good market drivers to use outboard checksumming.
> What I'd ask for is a knob toy turn outboard checksums off or on,
> and that the knob be off by default. That way, after an undetected error
> has pervasively curdled your filesystem *and* your recent backups, you
> have no-one to blame but the guy who turned the knob on.
I'm all in favor of a knob when I can get one, but I think you're crazy
to consider even that it might default to off. Setting the knob off by
default is a worse idea than not going to the trouble of building the
machinery. Such knobs are themselves major sources of bugs. Bugs asside,
what such knobs do do is often not understood by your own technical support
people, usually not understood by your sales people, rarely understood by
your customers, and a weakness that will be exploited by your competitors.
Too many of your customers would fail to turn it on, fail to get your
advertised benchmark numbers, and get unhappy. The salescritters of your
competitors would tell everyone that the fact you leave the knob off by
default proves that even you don't believe in it and so obviously your
whole system is junk. You will even have self-described experts whose
paychecks are signed the same as yours blabbering such stuff.
Yes, I've personally experienced all of that, having set off-board
checksumming to off by default in some interfaces.
As for curdling filesystems, if the feature is so new it doesn't have
system-years of internal use on production machines such as the systems
that do your vendor's nightly builds, simulate its future silicon,
and hold its many GBytes of RCS or CVS source trees, than yes, the
knob should be off by default. If it has all of that testing, then
you're vastly more likely to have a curdled file system from that
cheap, third-party SCSI cable you installed wrong last night than from
"out-board" TCP and UDP checksumming.
Vernon Schryver vjs at rhyolite.com
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