In comp.sys.ibm.pc.hardware.storage David X wrote:
What is the cost of DVD storage in the UK? I am in the UK so my figures
reflect UK prices. I want to store data not music.

I would welcome any comments on my posting.

[...]

Overall, I get the impression that HDDs are a far better and cheaper way of
backing up data for the home user. The HDD can be re-used and if the HDD is
plugged in (which can be harder than inserting a DVD) then the availability
is almost instantaneous.

Your calculation is missing one point: Redundancy.

If your Disks are e.g. in a RAID5 and are surface-scanned every 2
weeks, the sytem is going to be very reliable and your overhead will
be one disk per array and some hot/cold spares. Additional costs
include hardware, power and system administration.

If your disks are kept offline, you have to take into account
the possibility of catastrophic failure of one/several disks
and should actually have all data at least on two disks. This
still might give less reliability than the first solution,
depending on storage time/conditions and the disks. If the
disks are tested periodically, reliability will increase but so
will cost.

For your CDs/DVDs you also should put everything at least on
two media. If you do regular checks of the media, reliability
will increase, but so will cost. Also reliability figures
for CDs/DVDs are much less certain that for HDDs. The
30 years or even 100 years or more ofteh quoted by many
vendors 5 years ago have turned out to be wishful thinking
in many instances. It is better today, but nobody really
knows how much better. CDR and DVD+/-R are young technologies!
No long-term experience like with HDDs, Tapes or MODs exists!
And of course while the RAID5 has very low handling overherd,
you will be juggeling CDs/DVDs for hours to burn them, verify
them and generally handle them.

Of course, depending on the reliability wanted, you can do more or
less replication and you should have off-site copies for anything
important. You cannot simply take the media price. Storage cost is a
trade-off between cost, efort (also cost) and reliability. And you
need reasonable reliability estimates and estimates of needed
reliability and storage volume to make an informed decision.

Arno
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