fault tolerant web servers on freebsd

[Tonix (Antonio Nati)]

Maciej Jan Broniarz ha scritto:
> W dniu 10-04-05 22:08, Tonix (Antonio Nati) pisze:
>> Maciej Jan Broniarz ha scritto:
>>> W dniu 10-04-05 17:45, Mike Jakubik pisze:
> >
>> Just to use exact words, fault toulerancy is not possible with any
>> FreeBSD/Linux O.S.
>> F.T. means outage can occur in every moment, but all current operation
>> will be always completed by other equipments; so there will not be
>> interrupted/lost operations.
>
> Hmm. Thanks for the tip. Which *NIX os can be used to build an FT 
> solution then? Solaris? AIX? HP-UX?

For a FT solution you need usually an hardware solution, very expensive.
Server must have all doubled, with custom chips for checking if parts 
are working (and which part is broken, which may not be easy to understand).

VMware claims to have a software fault toulerant solution, syncronizing 
two servers in real-time, but I don't know the efficiency.

The most ISP use HA solutions, which are ok for the most of WEB/e-mail 
operations.

Operations are not available for a few milliseconds/seconds, depending 
on the architecture you use.

Just to complete, drbd+heartbeat are NOT FT. They are HA. When the 
master server goes down, backup server must acknowledge the new status, 
then mount the replicated disk (think to disk check!), then start 
services working on that disk. So this solution needs  a lot of 
seconds,  probably  minutes to work.

With a good carp architecture, you just need milliseconds.

Tonino

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