Currently I am using DVD+R discs to save my media library. I've been hearing from other people that hard disks are cheaper or not much more expensive compared to DVD media. Even if they in fact may cost quite a bit more including an enclosure, they would take up much less physical space and make it easier to read back the information.

What worries me is, how reliable hard drives are in long term? Is it true that after one or two idle years, an attempt to start the HDD would result in much damage?

If left unplugged and turned off, an external HD is as secure as anything. If your data is critical, it never makes sense to have only one copy, regardless of the media.

I don't think HDDs are cheaper. If you compare a 400 Gig HDD for 110 USD, thats 0,272$/GB and a 100 pack Verbatim spindle for 30 USD is 0,06$/GB.

Plus you deprive yourself of that wonderful feeling from burning, scanning, etc

best solution: keep both!

you never know if/when a disc might degrade or a hard drive will fry itself.

if the data is important enough for you to be asking this question then it's important enough for a redundant backup

Agreed. I'd keep copies on both HDD and optical media.

What is the expected lifespan of an unused HDD?

J7N:

HDD for long term storage is questionable, unless you are willing to have multiple drives & regular re-transfers IMO, some other users have highlighted some possible issues with HDD for longterm archival:

http://club.cdfreaks.com/showpost.ph...&postcount=137
http://club.cdfreaks.com/showpost.ph...&postcount=149

That is even less predictable than the lifespan of DVD media.
I have found that hard-drives don't like to be left unused for
long periods of time. The usual symptoms are a failure to spin
up when power is applied. I don't know whether this is caused
by the heads sticking to the platters or if it is a problem with
the bearings. The cure is to give the drive a gentle (or not
so gentle) shake when it is powered up. I have seen this
problem with drives that have been left in storage for
1-2 years.

I think an external hard-drive or a drive caddy would be
more reliable because you could power it up regularly.

I would favour the belt & braces approach and use both
optical and hard-drives to back up your critical data.
Don't put all your eggs on one basket. Use several
different brands of DVD media and store it under ideal
conditions. Don't keep all your backups in the same location
in case they are stolen or destroyed by fire.

It depends on the drive and if oem or retail, as an example wd Sada have a 3 or 5 year, But it you lose you stuff then the Warranty will not replace the data.
Use both.
Bruce

You forgot enclosure and Jewel case. Where I live it's 0.28125 vs 0.17021 units. However, I was going to save much time by switching to HDD. And time is money.

So the idea is now to have the same data on 2 hard disks. Let's assume I rewrite all data once a year. Would that be reliable enough?

Get a NAS box that supports RAID 5- you can power it on every once in a while and detect a parity failure before the entire matrix goes down.

J7n: no one can tell you what would be reliable enough. you could keep a perfect hard drive in a dry dark temperature controlled closet and power it up once a month and your house could catch on fire and destroy it. conversely, you could burn a set of dvds and toss them in a corner, dust them off 5 years later and wipe all the dust and crud off and they could still read...then you'd feel like the 2nd hard drive backup was a poor investment.

i think 2 copies of something is a reasonable backup. could something happen to 2 copies of the same data at the same time? sure...your house could catch on fire with your hard drive in it and your 1 year old could decide to teeth on your dvds on the same day...is it likely? no.

for my own personal use i think a hard drive and a dvd backup is secure enough. if I ever encounter an occasion where I lose both at the same time...well then that really sucks. but losing data under this circumstance is less likely than only having one copy.