As suggested also 'buffer storages'

buffer stock

ECONOMICS, FINANCE a large supply of a commodity (= a crop, metal, fuel, etc.) that is bought and stored when extra is available, and sold when there is not enough, in order to control its price and quantity in the economy:
Rubber prices fell to a four-year low, despite purchases for the buffer stock.
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COMMERCE, PRODUCTION extra products, supplies, etc that a company keeps, so it always has enough available to sell or use:
Management wants to keep a **buffer stock** of 500 units.

http://dictionary.cambridge.org/dictionary/english/buffer-st...

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Note added at 2 hrs (2017-08-07 08:38:28 GMT)
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Another Definition

Supplied maintained in inventory to protect a company from short-term commodity price fluctuations or shortages of essential production inputs. Maintaining buffer stock can protect a company from the perception of hardship during market downturns.

http://www.investorwords.com/16220/buffer_stock.html