# Validation

## Blockhashes and parent/child relationships

During the generation of the CAR files, Old Faithful validates that each block generated has the correct links with the parent/child. This includes validating that each epoch's last block/first block links correctly with the slots in the following epochs.

This ensures that there is a complete set of blocks from block 0 to the current block. 

## Proof of History

Old Faithful supports full validation of Proof of History. In OF1, every epoch’s PoH has been validated with one exception (see [Epoch 208](/usage/validation/epoch-208.md)).  Outputs from our validation of the history can be found at <https://files.old-faithful.net/\\><epoch>/poh-check-\<epoch>.log.&#x20;

For example, <https://files.old-faithful.net/100/poh-check-100.log>:

```
I1109 13:00:28.125613  217304 main.go:130] Roots: 1
I1109 13:00:28.125641  217304 main.go:133] - bafyreibqt2nvroysxlxctgb52xxn27ectsllv2xyka4qar7ga6vupmbs3i (Epoch CID)
PrevBlockHash: 47PrqQ4MJrT4G2GB7uHk5CdZadTKspB5HgDszzxHPJc2
EOF
I1109 13:15:10.275042  217304 main.go:345] Waiting for all nodes to be parsed...
I1109 13:15:10.275046  217304 main.go:347] All nodes parsed.
I1109 13:15:10.275049  217304 main.go:349] Waiting to receive all results...
I1109 13:15:10.292252  217304 main.go:352] All results received
I1109 13:15:10.292261  217304 main.go:354] Waiting for all assertions to finish...
I1109 13:15:10.292840  217304 main.go:356] All assertions finished
I1109 13:15:10.292847  217304 main.go:359] Last block hash for slot 43631999: FUPcPKdnNUWRrwyDqpyAdMqX7XH6rvGM7eEHYYN2KX6M
I1109 13:15:10.292855  217304 main.go:360] Number of checked entries: 110,592,602
I1109 13:15:10.292858  217304 main.go:361] Number of hashes: 345,600,000,000
I1109 13:15:10.292861  217304 main.go:363] Successfully checked PoH on CAR file
I1109 13:15:10.292862  217304 main.go:143] Finished in 14m42.167217686s
I1109 13:15:10.292864  217304 main.go:144] Read 196980689 nodes from CAR file
I1109 13:15:10.292870  217304 main.go:59] CAR file checked successfully
I1109 13:15:10.292872  217304 main.go:53] Took 14m42.170098595s

```

To run this check yourself, you use the poh-check-car tool from <https://github.com/rpcpool/poh-check-car>.  Sample usage of this tool:

```sh
$ poh-check-car \
	--workers=12 \
	--auto \
	--epoch=0 \
	--car=/media/laptop/solana-history/cars/epoch-0.car
```


---

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