No, I was doing a fast sync (but not a light sync, which is different). I wanted and got the transaction history & full code for each smart contract on the chain, but didn't care about verification of each transaction in the chain.

You can run a full node that verifies everything on an ongoing basis without doing a full sync from the genesis block - just start it in fast sync, let the chain catch up, and then run it again in full mode. Unless you believe the Ethereum blockchain has already been compromised, there's no reason why your personal node has to verify everything from the genesis block.

gcmode=archive is not required for a full node. It indexes every transaction in a database, which is unnecessary for most applications. It’s similar to txindex in bitcoind, but the Ethereum db is already much larger, so it takes weeks to sync in this mode.

I see, the problem was that it's hard to find documentation about what's needed for an Ethereum full node. As I'm just running Bitcoin full node, I don't have any personal experience with it.

Parity CLI options: https://wiki.parity.io/Configuring-Parity-Ethereum#cli-optio...

Geth CLI options: https://github.com/ethereum/go-ethereum/wiki/Command-Line-Op...

Understand the differences between syncing, validating, and pruning, then it becomes simpler... https://github.com/ethereum/go-ethereum/pull/1889 https://github.com/ethereum/go-ethereum/wiki/Tracing:-Introd...