need to have
services available
remotely managable
all open source software (backdoors, ability to fix security issues)
no "trusted computing" hardware (backdoors)
timed responses on SSH logons
http://home.nuug.no/~peter/pf/en/bruteforce.html
write logs to different server on write-only media
least number of users, but redundant administrators
least number of services
backup server
backup power (UPS, generators)
Rule 1: Always make a backup.
Rule 2: Always make a backup.
Mirroring: High availability
Backups: High reliability
The rules of backups:
1. Backup all your data
2. Backup frequently
3. Take some backups off-site
4. Keep some old backups
5. Test your backups
6. Secure your backups
7. Perform integrity checking
rm -rf /
That is one reason why mirroring isn't a backup, and why backups should ideally be off-line.
DR is Disaster Recovery
HA is High Availability
It's more an issue that some people think that HA == DR.. which obviously this story reminds us that it is not the same thing.
Mirroring / RAID == HA.. if one of your HDDs let the smoke out, you still don't incur downtime. If you have a hot-spare, you're even better.. all it does it let you have alittle time to correct the
issue (ie: "It can wait until morning").
Also, one other very important thing.. mirroring doesn't prevent/restore data corruption. If you're mirroring your rm -rf (as pointed out by Corsec67 below), your RAID will happy do what it does.. and span your command to all your disks.... Congrats, you just successfully gave yourself HA to your disk erasing! :]
Backups are DR.. If your RAID croaks.. your SOL if you don't off-machine backups. If you accidently nuke your disks with an rm or something, you can still go back and restore data.. sure you'll likely loose -some- data, but -some- is better then all in this case.