Re: Re: endb 101

Hello Peter,

thanks for your reply.

Quoting "Peter T. Breuer" <[email protected]>:
> The whole idea of fallover is that you have a "floating IP address"
> that moves between two machines, according to which of them is acting
> as the server at that moment. That "primary" (A), when it breaks, passes the
> IP over to the "secondary" (B), which has an up-to-date mirror copy of
> the data to serve from.

ah, i guess i forgot to mention: There Is No Such Thing as "floating IP
addresses" - at least in my case :-\
machine A and B are located in different hosting centers with static IP
adresses which i am not allowed/able to change, but try to work around this
issue by using names instead of ip-adresses for my services and have to update
the DNS records quickly...

> It's also normal to have TWO floating IPs, and TWO resources on each
> of TWO servers. One resource on each server acts as a remote mirror
> for a resource on the other server.

yes, that's the thing that confused me:

     "One resource on each server (hda3) acts as a
      remote mirror (nda0) for a resource (md0) on the other server."

but now i see, that only A will have md0, B will serve from hda3 only.

>> so then it's like this:
>>
>> machine-A: md0 [hda3+nda0]
>>
>> machine-B:     exporting hda3, but were do the applications
>>                 write to?
>
> What applications?

database, webserver, mailspool. they're running on A, using md0. if A is down, B
takes over, the applications will start and will find the same data on its hda3
(because it was exported to A until A crashed...).

>> i *thought* all machines could
>> carry an md0. i was wrong. hm.
>
> They can, and you are not wrong. There is no reason for B to use a
> mirror (in degraded mode) while A is running, but it can. It would
> make things a little easier for when A comes back up again.

yes, ok.

i'll look over your other comments with my co-pilot, as there are still some
requirements we need to sort out on our side. eventually he'll even write to
the list too ;)

thank you so far,
Christian.

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