What do people think is a better way to store large volumes of date, either external hard drive or blu ray disk???
Depends how much. I'd rarely recommend Bluray disks. Small amounts of data (maybe 100-200GB) dual layer DVDs. Moderate amounts of data (200-2000GB) an external hard drive. Large amounts of data (2000GB+) a file server PC.
It would help if you specified what big is and how valuable the data is. Cost and reliability are the main issues. Hard disks are the most reliable especially over a few years. You can use eSATA or USB external box put in load up a HD then remove the disk and put it on a shelf. Most of the ones I have seen only have 2 screws. Swapping idsks takes less than 5 minutes even if you are slow. You can put all your old junk HDs to work that way. TB disks run for about 100 USDs. DVDs are the cheapest repository but a great deal of care needs to be taken in burning and verifying the disk. I don't use them for valuable data any more.
You can actually get hotswap usb/esata drive enclosures that don't require screws. Also bear in mind HDDs may be more reliable than DVDs but can easily be irreparably damaged.
Good point, I have never damaged any of mine but then I don't use a hot swap just for that reason. If you swap while there is no power, you do not have much of a change of breaking it unless you drop it on a hard surface. I actually unplug mine you are sure not to have power then.