1. A method for throttling cache updates in a storage system having a caching device and a storage device, the method comprising: for each of a plurality of write periods of the storage system, each of the write periods having an associated threshold number of permitted writes to the caching device, receiving a request to read data that is stored on the storage system, and, upon determining that the requested data is stored on the storage device, but not on the caching device, then: (i) if a number of writes to the caching device for the write period is less than or equal to the threshold number of permitted writes, reading the requested data from the storage device and storing the requested data in the caching device; otherwise, (ii) if the number of writes to the caching device for the write period is greater than the threshold number of permitted writes for the write period, reading the requested data from the storage device without storing the requested data in the caching device.