What is/are the rules of thumb in choosing between dedicated and VPS options (not sure I know the diff either)? My paramount concerns are availability, managed services, and security. My site activity is very inconsistent - 75% of the time bandwidth rqmts will be very low, a few hits a day, remainder periods demand likely to be extremely high, possibly up to a couple hundred thou hits a day). The site is critical to users - can't be down, ever. Backend DB MS SQL Server 2005.
Couple hundred thousand a day should be easy for a standard dedicated server to do. That's only a few a second. Unless its all loaded into a few hours of that day you shouldn't have a problem. A vps may not keep up, its hard to tell due to the amount of ram you would need. If they are dynamically generated pages it would be a cinch to do on a dedicated with something like eaccellerator and a ton of ram set aside for it.
A vps, you might want to set up some kind of failover system in case it doesn't keep up.
edit - Nevermind all of that, I didn't see the mssql part of the question. That voids any advice I could give.
Dedicated will have better up time.. (More things to go wrong in a VPS, and more things that you don't have any control over).
But if you REALLY need 100.00% (and 99.99% won't do) then you need to look beyond a single dedicated machine. 2 machines and a pair of expensive routers should get ya close.
if 99.99% is ok, then a well thought out dedicated in a quality data center should get you there.
IMHO most VPS will crumble well before a couple hundred thousand hits a day. Even without exim, cpanel, and msSQL running..
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