# Storage proving Storage proving, known as *Proof-of-Spacetime* (“PoSt”), is the mechanism that the Filecoin blockchain uses to validate that storage providers are continuously providing the storage they claim. Storage providers earn block rewards each time they successfully answer a PoSt challenge. ## Proving deadlines As a storage provider, you must preserve the data for the duration of the [deal](/reference/general/glossary.md#deal), which are on-chain agreements between a client and a storage provider. As of March 2023, deals must have a minimum duration of 180 days, and maximum duration of 540 days. The latter value was chosen to balance long deal length with cryptographic security. Storage providers must be able to continuously prove the availability and integrity of the data they are storing. Every storage sector of 32 GiB or 64 GiB gets verified once in each 24 hour period. This period is called a *proving period*. Every proving period of 24 hours is broken down into a series of 30 minute, non-overlapping *deadlines*. This means there are 48 deadlines per day. Storage sectors are grouped in a *partition*, and assigned to a proving deadline. All storage sectors in a given partition will always be verified during the same deadline. ## WindowPoSt The cryptographic challenge for storage proving is called *Window Proof-of-Spacetime* (WindowPoSt). Storage providers have a deadline of 30 minutes to respond to this WindowPoSt challenge via a message on the blockchain containing a [zk-SNARK](https://en.wikipedia.org/wiki/Zero-knowledge_proof) proof of the verified sector. Failure to submit this proof within the 30 minute deadline, or failure to submit it at all, results in *slashing*. Slashing means a portion of the [collateral](/storage-providers/filecoin-economics/fil-collateral.md) will be forfeited to the f099 burn address and the *storage power* of the storage provider gets reduced. Slashing is a way to penalize storage providers who fail to meet the agreed upon standards of storage. [Was this page helpful?](https://airtable.com/apppq4inOe4gmSSlk/pagoZHC2i1iqgphgl/form?prefill_Page+URL=https://docs.filecoin.io/storage-providers/filecoin-economics/storage-proving) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.filecoin.io/storage-providers/filecoin-economics/storage-proving.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.