[cd34]

100% means different things to different people. Some SLAs (Service Level Agreements) talk about 100% network uptime to certain providers, or 100% facilities uptime. And 100% to where? 100% to a router, to a group of routers or points on the net? 100% uptime to whom? If you are singlehomed at home, and your cable modem goes down, your site is down to you. Obviously that is beyond the scope of a hosting company.

Fives 9s is another common uptime phrase, meaning 99.999% uptime which is roughly 5 minutes of downtime per year.

Getting closer to that 100% gets expensive. You start having to deal with load balancing, clustered filesystems, specific architectures with the software running the site and being able to split processing smoothly without introducing other bottlenecks. Mixing 100% uptime with realtime performance gets very difficult.

With that said, hardware fails. Having a provider that can get to the equipment quickly, diagnose and fix the problem is important. Again, that doesn't come without cost.

So, it depends on how critical your business is, and the cost is that comes with that uptime. Then you have to balance that with security issues. Recently there have been some kernel security problems (last 6 months or so) which required a reboot. Without a cluster or failover setup, depending on the filesystem on the hard drive, its last check, the size, the number of files, you could easily eat a few minutes on a reboot. Its not like any OS is really immune to that. SP2 was recently released. FreeBSD had an issue with jailed routing and procfs, Linux had a recent issue with Denial of Service Handling.

For a single machine, I don't believe 5 9s (99.999%) is attainable without luck and somewhat expensive hardware.

The other thing you have to take into account is recovery time. In the event of a hard drive crash, how long is it before you are back online with your data in place. Your machine may be brought back to life in 15 minutes, but, if you have no data, you're really no better off than if you were down -- perhaps even worse off. Since you have no data, you would be handing out 404s which could remove you from a lot of link checkers. A 'down' site usually won't result in you being removed immediately.

Its also not impossible for a poorly behaved application to take a server to the point where it is up, but not responding quickly enough. Hardware and network are fine, but, Apache/php/mysql might have bogged the server to a point where you would consider it down.

You need to look for another host when you feel that you aren't getting the service you are paying for, or the response that you need. If your requirements for uptime exceed what the current provider can offer you, then, you need to consider moving. Jumping to an unknown isn't without its issues as well. Moving your sites can be somewhat traumatic. Many hosts will help you with this, but, sometimes debugging the sites after they have moved can be time consuming.

Basically, its a decision you have to make for yourself. If you are paying nickels for hosting, then you are going to make some sacrifice somewhere.