multiple nameservers - increasing reliability?

a very basic question....

[Algebrator]

Recently, I have such a bad luck finding a reliable hosting company (despite all the good advice at WebmasterWorld). They all self-rate themselves with 99.99999999... uptime, which is just a bunch of lies.

Please tell me what would happen if I do this:

1. get two hosting accounts with two different companies
- each gives me two name servers
2. I update the nameservers at my registrar by using all 4 nameservers
3. both accounts are mirror images of each other at all times

What happens when one server fails? Do I have increased reliability, or do wierd things start happening which, due to my ignorance on the subject, I am not able to forsee?

A side note - I would to this just on a single site for which it is absolutely necessary to be up ALL the time, so I wouldn't mind extra hassle and expense

[dvduval]

Well, that won't work exactly, but these days when you make a change to the dns record it usually only takes a minute or two, so if you have two hosts and one goes down, you can quickly switch the nameservers.

[larryhatch]

My domain registrar (tbe former monopoly) allows a primary and secondary DNS.
For now, they both point to my sole site host.
I presume I could have a second host ISP and put them in as secondary.

Both would be identified as www.mysite.net, so I presume there are no duplicate content issues.
Is that a safe assumption? -Larry

[Algebrator]

dvduval,

Could you briefly explain why it wouldn't work - what is the 'protocol' here?

The problem is that I would like for this to happen automatically (as it presumably does with two nameservers used by a single host) - not few hours later when I find out about it.