Question like in subject. Storing data on optical drives is by me first: expensive, second: takes alot of place, third: optical disks are fragile to time and unpractical for mass storage (if you think not, you should see my wardrobe ).

So I thought I would just buy 2-3 4TB Drives and would get my whole file library to HDD.

Pros: Fast access, low space requirements, lower storage price, possible encryption, SMART for control over data.

Cons: That's the question.. what are cons? Except power consuption for NAS.

When HDD is unplugged, and unpowered at all. How long does data retain on it? Or there is no difference? Probably still longer than common optical disks that with time can break. Especially low quality ones.

Definitely longer than optical disks or NAND flashes
Biggest con of HDD is that HDDs are fragile

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SAN, NAS, RAID, Server, and HDD Data Recovery.

Hello. Thanks for answer. Fragile in what way? You mean "dropping" it on floor? or other kind of fragility?

HDD is a precision mechanism and its correct functioning depends on certain conditions:
1. Correct temperature range
2. Correct humidity range
3. Correct altitude range
4. Clean air
5. Limit of mechanical shock/vibration (even tapping on a running HDD could be fatal)
6. Good power supply
7. Correct running time (cheap HDDs cannot be run 24x7)

Even with all that there is no guarantee that particular HDD is free of mechanical or firmware problems

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SAN, NAS, RAID, Server, and HDD Data Recovery.

Pulled one out of the shed that must have been 10 years or more since bootup (whole PC) it has win for workgroups 3.11, booted like it was supposed to, seen no issues at all. It must be a GB or less HDD, cant remember.. its back in the shed, where it belongs, LOL!

Thx Doomer. Humidity in room is normal i think (what is recommended humidity?). my HDDs are 4 and cooled with additional FAN, so they're around 35-38C since air flows between them. So any new would be held in same conditions . I mainly use Chieftecs... not any no-names so shouldn't be problem too I think.

I thought HDDs are hermetic, and air pollution does not affect it.... And true... manufactured defects are hard to forsee... but I think I still have more chances to keep my data with SMART monitoring. My CD wouldn't inform me its going to split its layers, and some do.

@HaQue Great info. Still 1 GB had lower block density and new HDDs (like few thousand times?) may be more fragile for those effects. My 4GB Seagate U4 is immortal too ^^.

You can read HDD specs for recommended levels of humidity
HDDs are not air-sealed, although they have air breathing filter, its abilities are limited. For example: cigarette smoke could still get inside in small capacities.

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SAN, NAS, RAID, Server, and HDD Data Recovery.