Currently, you can't upload data to Walrus directly from a Solana smart contract or a Sui smart contract. You'll need to handle the data collection and storage to Walrus off-chain. Once you store the data with Walrus and have the blob IDs, you can reference and store them on-chain using Solana if needed. Walrus blobs are meant to be managed through off-chain protocols, with their certification managed on the blockchain like Sui. For storing off-chain with Walrus, the data is first encoded into slivers and distributed across storage nodes. The storage of blobs in Walrus can be extended for long-term guarantees, but modifying the data itself would require new uploads and certifications.

On-chain storage references the metadata and pointers to the actual blob data stored off-chain on Walrus. This means the content of blobs is stored off-chain, providing flexibility and reducing costs. Ensuring the security and validation of the data with a Solana smart contract would require checking against the certified Walrus events stored via Sui or similar on-chain events. It's crucial to ensure the hashes match during retrieval to confirm data integrity.