Data storage amount limit exceeded

If your organization's active production instance shows as nearing, almost over, or at 100% of its available storage, it will continue to run as expected without any effect on your applications. At some point, beyond 100%, performance will be degraded. The exact point at which degradation will occur depends on the specifics of your implementation and cannot be predicted exactly. For this reason, it is recommended that you do not exceed available storage limits, or otherwise increase your storage limit

Notes:

• If you use Sandboxes, keep in mind that storage limits are strictly enforced for Full Sandboxes.
• For example, you are at 110% Data Storage in Production and you refresh your Full Sandbox. It is an exact copy of Production and so your new Sandbox is also at 110% Data Storage. As storage limits are strictly enforced for Sandboxes, it would not be possible to create records in this new Sandbox.
• If storage was recently added to Production and the increase is not showing in the sandbox, the Match Production Licenses to Sandbox without a Refresh tool can match the storage.