I have a 4TB HDD where all my photos and related files live. This drive is named "PHOTO".
I backup this drive in two ways:
1. External USB enclosure which holds 8 disks. My other HDDs are also backup up to other HDDs in this device.
2. My computer case has an open slot for HDDs accepting 3.5 and 2.5 HDDs. Basically I can use internal SATA disks as you would use floppy disks, they are hot-swappable.
Backup software: I use SyncToy and SyncBackFree and simply mirror the PC drives onto backup drives.
Some people will say there are more sophisticated ways than mirroring but I am afraid that the backup file might go corrupt at some point. With my method I have (at least in theory) exact copies of my drive.
Of course I back up the raw files and Ligtroom catalogues. They are most important.
Folders and file management:
I use Lightroom to manage RAWs, TIFFs, PSDs only with basic keywords allowing me to find the photos quickly.
I manage JPGs in AdobeBridge using a "batch system", e.g. BATCH 2013-01. Each agency has a separate folder and the BATCH folders are pasted into Agency Folders. I upload them immediately. This way I know which batch has been uploaded to a given agency. After some time I delete the jpg files from agency folders leaving empty folders to save space while keeping track and they stay only in one master folder e.g. BATCHES - 2013.
I don't care if an agency rejects a photo and usually don't go back to it. Most are accepted anyway.
I am thinking about renting a small bank safe and keeping some back up drives there. It is recommended to keep at least one backup offsite. Bank safes are much cheaper than online storage but you have to make a trip to the bank from time to time.
Regarding raws: i understood and have seen that is not so easy to backup a raw file. The changes are saved by lightroom in a separate folder. So in case you want to move a raw on a backup disk what do you do? I found out that is complicated.
No, the changes are stored in the lightroom catalogue file. You just need the RAW files (keeping the original folder structure) and the LR catalogue file to recreate your photo library on a new drive or machine. Just write down the partition letters where the raws are stored. When you move your stuff to a new drive just assign the same letter to the new partition (e.g. Start > Computer > Manage > Disk Management). I've done it several times, it's painless. You don't need to care about preview files, they can be recreated automatically.