Let's get something straight...
RAID can "be" a backup. You can backup to hard disk all you want. There is nothing wrong with that, in fact here in the office, my backup system is hard disk. Both faster and cheaper than Tape.
If you only have a RAID system, you do not have a backup, you have redundancy to protect from a drive failure. A backup, by definition is a second (or third or fourth) COPY of your data. That copy can be on any media you want. Even a hard disk. But, a RAID system alone is not a backup.
If you copy all of your data from your PCs hard disk to a second hard disk, then it IS BACKED UP.
If you make a hard disk copy of your data and that drive fails, make another copy, you have a backup.
Here in my office, I use 750GB hard disks as backup media. Nightly backups are done to hard disk. After the backup is complete, the backup drive is copied to a second drive. So, I have the original data on the RAID 5 system in the file server, and I have a complete incremental backup on a hard disk and a second copy of that backup drive. My data exists in 3 places at the same time. If the RAID system were to have complete failure, I could restore it from either backup drive. If one of the backup drives were to fail, I could make another copy from the other backup drive.
Incremental backups are nice, in that not only do you have a copy of what is on your hard disk right now, but you also have a copy of what was on your hard disk all the other times it was backed up as well. So, if you change a file on Friday, and then change it on Monday, then you wish you hadn't changed it and want the copy before Friday's changes, you can go back and get them.
I keep a copy of all files from every day for 2 weeks, and I keep a copy from every month forever.
RAID can "be" a backup. You can backup to hard disk all you want. There is nothing wrong with that, in fact here in the office, my backup system is hard disk. Both faster and cheaper than Tape.
If you only have a RAID system, you do not have a backup, you have redundancy to protect from a drive failure. A backup, by definition is a second (or third or fourth) COPY of your data. That copy can be on any media you want. Even a hard disk. But, a RAID system alone is not a backup.
If you copy all of your data from your PCs hard disk to a second hard disk, then it IS BACKED UP.
If you make a hard disk copy of your data and that drive fails, make another copy, you have a backup.
Here in my office, I use 750GB hard disks as backup media. Nightly backups are done to hard disk. After the backup is complete, the backup drive is copied to a second drive. So, I have the original data on the RAID 5 system in the file server, and I have a complete incremental backup on a hard disk and a second copy of that backup drive. My data exists in 3 places at the same time. If the RAID system were to have complete failure, I could restore it from either backup drive. If one of the backup drives were to fail, I could make another copy from the other backup drive.
Incremental backups are nice, in that not only do you have a copy of what is on your hard disk right now, but you also have a copy of what was on your hard disk all the other times it was backed up as well. So, if you change a file on Friday, and then change it on Monday, then you wish you hadn't changed it and want the copy before Friday's changes, you can go back and get them.
I keep a copy of all files from every day for 2 weeks, and I keep a copy from every month forever.