Marc Farley makes some interesting comparisons to storage purchasing decisions in a recent post. For the sake of disclosure, I do go to Costco and buy in bulk - no not 200lbs of chicken wings, but those things that can be divided and/or frozen (like salmon and coffee) - and more crucially things that don't become cheaper in price over time.
That is effectively Marc's argument; don't buy stuff you don't need yet because it will be cheaper in the future (not so with my salmon and coffee, I suggest). That's certainly true as we see a year on year reduction in storage per GB cost.
There are a number of reasons why people buy more than they need;
- New hardware deployment time is excessive due to datacentre restrictions and change control. In some sites this delay could be 3-6 months, so people work on the assumption that it's better to have more on the floor than be in a panic to deploy at the last minute.
- Business customers can't plan. It's a truism that everyone knows. Add on top the fact that chinese whispers inflate the original business requirement to two, three or four times more storage than actually needed.
- Vendors give discounts. Yes, shock! Vendors will sell you storage cheaper if you buy more. I know many places that buy complete arrays up front (even DMX-4 with 1920 drives!) to avoid the deploy time and get a better price.
There are many more reasons than this but you get the idea.
I've deliberately left off one issue - the inflexibility of some storage systems in their deployment method. Although this isn't directly a reason to buy more storage, it is certainly a reason why users hoard more storage on their servers. Monolithic arrays are way too slow at executing on configuration tasks and on dynamic rebalancing, requiring too much planning and thinking time to avoid bad layout and configuration issues.
So Marc, you should have stated that thin provisioning is only one aspect of reducing storage hoarding. Good practice is another. Flexible technology is an undoubted third.
Oh and 10 house points to the first non-UK person who can explain my post title!