I have a lot of pst outlook backups burned in about 200 DVD containing data from 2003 - 2013 . In year 1995 we start making backups on CD, later we move to DVD and DVD-Double Layer for backups. Now we are moving to Bluray backups. 25GB disks are now cheap and is a very good move.
As we always make backup of the backup and keep a copy off-site, we have an extra copy of this content in an external Seagate HDD
Unfortunately, the copy failed in 2011 (HDD click of dead). We then copy the 200 DVD contenst to a new HDD (WD 2tb mini HDD USB3). This unit fails last year as well.
So we move to another option: Created a raid5 in a buffalo NAS and one disk fail this 2013. Get a replacement and during rebuild, a 2nd disk fails and we lost all data.
So we are really concerned about reliability in HDD for long term backup (thank God we have the pst...