I have a small server at home which utilizes ~ 8 TB of space.
This year HDD-Diety has pointed the bone at my system - 3 various drives have died within half a year, including one of the backup drives (it was just sitting of the shelf for the past year). So i am left with just a desync'ed pool.
What other reliable and preferably not expensive options are there for backup? Does anyone use the tape drives? is that reliable? OR better stick with HDD - which one's better for this job?
I would suggest avoiding tape drives for personal use, they're insanely expensive, not much more reliable than hard drives and with the typical max tape sizes being measured in double digit gigabytes, you'll be sitting by the system for a couple hours waiting to change out tapes in the drive when running backups.
While it doesn't exactly fit the 'inexpensive' requirement, I would recommend using a service like Amazon S3. Most FOSS backup software supports S3 style storage API's for storing data, and it's generally pretty easy to set up. However, for ~8TB of data, you would be looking at roughly 200 USD a month in storage costs for Amazon S3 with the basic storage option, and about half that for the IA storage option (which is good for backups), with similar pricing from most other competitors. You could probably easily bring that down by just backing up what you actually need to (for example, you probably don't have to backup the OS itself, just the configuration and a list of software that's installed), and using compression (which may be able to cut your space requirements significantly depending on what type of data is involved).
Blu-Ray disks might be an option also if you don't need to store all the data (but aren't exactly cheap, and you would need a lot of them since they hold at most 100 GB for the dual-layer ones). If using optical media like Blue-Ray disks, make sure to use the lowest writing speed possible, as data retention of writable optical media directly correlates with the write speed (slower write speeds result in the laser focusing on a given spot longer, resulting in better retention).
If you have to use traditional hard drives, I have a couple of suggestions:
Avoid using USB or Firewire to connect them if possible, as both have reliability issues. eSATA and external SCSI/SAS connections are more reliable, an internal hot-swap drive bay is even better.
Avoid SSD's. They don't have very good long-term data retention when not being used regularly.
Spend the extra money on Enterprise or NAS rated drives, they're generally more reliable (but not neicarily more durable).
Store multiple copies of each backup, ideally on separate media. This really applies to any backup system, but many people don't think about it when dealing with removable hard drives.
Get proper impact resistant and ESD safe cases for the disks to store them when not being used. These typically cost about 10 USD each most places, and provide protection against the two biggest threats for traditional hard drives.
If possible, integrate some form of erasrue coding in your backups to protect against data corruption. I would personally recommend PAR archives for this. Ideally, this should be used after compressing the backups for performance reasons (and because it doesn't compress well).
