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I have a 100MBPS connection that is over 99% reliable.
Wow -- nice!
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But im not really sure what kind of disk i should use or how to download the server info onto my disk. Any suggestions?
The kind of disk doesn't really matter at all.
What OS are you running on the server? Control panel?
Is backing up your data sufficient, or do you want to do something more advanced and quite difficult? (most probably just backup their data and if the worst happens, order an os reload, reharden the os (removing unneeded services, installing intrusion detection, firewall, lock down permissions, etc.) reconfigure services, and reinstall the backup data)
How often do you want to backup your data and what retention do you desire (since you have ample bandwidth).
E.g. "on the cheap" with an old computer and $99 500 GB drive, you could rsync to incrementally backup to a local system weekly and then simply archive (tar.gz) the backup directory monthly to keep x-months of "snapshot" backups in case you ever need something "as it was".
I'm sure there is a more elegant solution, but if you have an old computer or $99 drive this could easily get it done quite sufficiently.