19-MAY-2006

First I managed to fit my entire photo collection on my hard drive, then my music archive and in one or two years I hope to have my video archive on my hard drive as well.

If your storage needs grow linearly and storage prices keeps dropping logarithmically, eventually the cost for an additional year will quickly become neglectable and even a new solution for the entire archive will eventually become quite cheap - actually a solution for the entire archive will after four years be cheaper than the solution for archiving only the first year.

My example is based on archiving one audio stream 24/7 for one year at 256 kbps and prices are in euros. Perhaps not a typical need, but this exemplifies the linearly growing archive.

Every year results in 1 TB of data. After the first year there will 1 TB in the archive and that will cost about 700 euros. After 10 years, the size of the archive will have grown to 10 TB but by then, one additional TB will cost only 7 euros and a solution for the entire 10 TB archive less than 100 euros.

When talking about bitrates today, one k (kilo) usually refers to 1000 and not 1024 like it used to. And if bits (b) and bytes (B) are unfamiliar to you, remember that it is not the same thing, one byte equals 8 bits. Please note that I use , as a decimal delimiter.

Per second: If we record audio at 256 kbps (kilo bits per second), we are recording 32 kBps

(kilo bytes per second) since 256/8 = 32.

Per minute: 32kB per second gives us a total of 1920 kB (32x60) of data every minute.

Per hour: With 1920 kB of data gathered every minute, we will end up with a total of 115200 kB.

per minute (1920x60), and converted from kilobytes (kB) to megabytes (MB), that is 115,2 MB.

Per day: In one day, we will accumulate 2764,8 MB (115,2 x 24), expressed in gigabytes (GB), that equals 2,7648 GB.

Per year: With 365,25 days in a year, we will end up with 1009,8432 GB. Lets round that to 1000 GB per year, or expressed in terabytes (TB) 1TB.

A one terabyte disk array, the kind that is intended for private or small business use, costs about 700 euros today (spring 2006).

If we keep archiving this audio over the years, we will need room for one more terabyte every year. We will have 1 TB after the first year, 2 TB after the second, 3 TB after the third and so on. In other words, our storage need grows linearly. But this does not mean that we will have to spend 700 euros per year on storage as the price of storage drops from year to year - and it does so logarithmicly. The cost of storage drops at about 45% per year, but to be on the safe side, we will assume that it drops by 40%.

After the first year we will need 1 TB and pay 700 euros for it. After the second year, we will need 2 TB and we will be able to get the additional 1 TB for 420 euros - or replace the old storage solution with an entirely new 2 TB solution at about 840 euros. What about three years? Well, we can by the additional 1 TB for the third year at a price of about 250 euros or an entirely new 3 TB solution for about 750 euros. And the fourth year, we can buy the additional 1 TB for 150 euros or a 4 TB solution for about 600 euros.

THIS is interesting, because now the storage solution for storing our entire four years is actually cheaper than it was to store just the first year.

With our storage needs growing linearly and storage prices dropping logarithmically, eventually the cost for an additional year will be neglectable.

Real life will of course not follow this example precisely and most importantly the disk array I used in my example is not suitable for everyone. If you would like to go with adding plain hard drives the prices will be about 25% cheaper than in my example, and if you wish to go with a high end fault tolerant enterprise storage solution with all features, the prices will be about five times higher than in the example. Nevertheless, these issues will not affect the general result here about the storage solution becoming cheaper after about four years.