[Drbd-dev] About the UUID

[Drbd-dev] About the UUID

[home_king]

hi, Philipp.

Now drbd-0.8.x uses UUID instead of GC as the data-relationship-detection
-tool, right? Its logic seems clearer than GC. However, I am confused
about the UUID in the two-primaries-healedpartition scenario.

Given the original uuids below (both nodes are connected):
P <5,0,0,0>      S <5,0,0,0>
then, I plug out the wire of the primary node (disconnected):
P <6,5,0,0>      S <5,0,0,0>
I let the downgraded secondary become new primary, UUID should become:
P <6,5,0,0>      S <6,5,0,0>
Finally, I recover the wire of primary. And Now, there comes my problem.
Accordding to the UUID algorithm, when Cs == Cp, no resynchronisation
necessary. However it is obviously split-brain, and drbd ignores it.

Why?

BTW, I did not test such scenario, because I can't compile drbd-0.8.x
in my RedHat AS4 distro. I just browsed the doc & code. :-)

Regards,
luo.jinhua

Re: [Drbd-dev] About the UUID

[Lars Ellenberg]

/ 2006-12-20 15:06:57 +0800
\ home_king:
> hi, Philipp.
> 
> Now drbd-0.8.x uses UUID instead of GC as the data-relationship-detection
> -tool, right? Its logic seems clearer than GC. However, I am confused
> about the UUID in the two-primaries-healedpartition scenario.
> 
> Given the original uuids below (both nodes are connected):
> P <5,0,0,0>      S <5,0,0,0>
> then, I plug out the wire of the primary node (disconnected):
> P <6,5,0,0>      S <5,0,0,0>
> I let the downgraded secondary become new primary, UUID should become:
> P <6,5,0,0>      S <6,5,0,0>

no. these small digits are only more readable examples.
our UUIDs are 63bit random numbers.
they may clash, and we have to fix that somewhen.
but that is not very likely.

we probably should change the example to read more like
head -c8 /dev/urandom | hd
<3cecd7aed66ff5ad,0,0,0>		<3cecd7aed66ff5ad,0,0,0>
<dc855810336641b6,3cecd7aed66ff5ad,0,0>	<3cecd7aed66ff5ad,0,0,0>
<dc855810336641b6,3cecd7aed66ff5ad,0,0>	<44dc24617bd63967,3cecd7aed66ff5ad,0,0>

to make this more obvious.

> BTW, I did not test such scenario, because I can't compile drbd-0.8.x
> in my RedHat AS4 distro.

works for me.

-- 
: Lars Ellenberg                            Tel +43-1-8178292-55 :
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