Back up server issue

[varun8211]

I have 1 linux dedicated server. I am hosting 10+ websites on it..
I am thinking about the purchsasing a new server from other host that I will use as back up server at the time of needs (when primary server goes off)..

How can this be possible? I have heard about mirror servers..

Also when I shift to new server, I will have to change the DNS on every domain with my domain registrar and that will take 48-72 hours to come into effect.. Can I change or interchange the IP (DNS settings ) of each server so that I need not have to change DNS for every domain./??

I am willing to transfer the data from one server to other weekly of fortnightly...

Please provide me with other helpful details..

Thanks

[Rincewind]

I think what you are describing is more correctly termed as a "fallover" server rather than a backup. Strictly speaking a backup is use to resore the system to the origonal server in the even of data loss where as a fallover server take over the system in place of the origonal server.

A fallover server usually contains a exact copy of the current main server. Evern change to the main server is replicated to the fallover so that both can be used at any one time. Where as a backup usually contains an old, out dated version. Or more correctly many old out dated versions of the main server. The idea is that if a alteration of data on the primary server causes a problem, then you can revert to the backup version. You can never revert to the fallover server.

Basically the two systems do two different jobs. A backup protects you against data errors where as a fallover protects against hardware failures. In general, it's prudent to have both systems running. It is possible for your fallover server to also contain the data for the backup(s) if there is sufficient hard disk space.

Fallover servers, particularly for sites that change allot (e.g. this forum) require large amounts of bandwidth. Every change to the main server must be replicated on the fallover to keep it up to date. So your bandwidth use can be very high. Normally, people set up the fallover so that is physically close to the primary server (in the same rack) so that the transfer for the mirroring is done directly form server to server in a LAN and avoides going through the datacenter's/isp's and paying their bandwidths.

One of the simplest fallover systems you can set up is simply to use a RAID setup. RAID means a Redundant Array of Inexpensive Disks. In RAID, each disk acts as a fallover to the other disk. If one disk fails, the other takes over instantly. This provideds a basic fallover service to protect against disk failure without having additional machines.

It should be remembered that RAID is not a backup. You still need to make backups to an external server periodically.