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0 pointsscienceman7y ago0 comments

Not OP, but probably to make sure the contents of a file are not changed by hardware errors.

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Yep, otherwise you aren't able to detect bit level errors unless they impact the metadata, and the metadata is a tiny fraction of your total storage.

That said, your hard drive already does block level checksumming so doing it at the FS layer is mostly redundant unless the errors are being introduced in your SATA controller or on the PCI bus.

aaaaaaaaaab7y ago

You would still need end-to-end integrity checking, unless your Mac came with ECC memory (which it probably didn't).

mcpherrinm7y ago

Memory errors are still a concern, however, RAM is not used for persistent storage.

If a bit flip occurs during the path to storing data, that could get persisted. That's a moment in time, though. Maybe you'll notice the document you just wrote seems corrupted, or just has a typo.

But if you write successfully to disk, you are trusting that data to stay there long-term. If years later your drive corrupts a bit, you may have a very hard time noticing. Bad RAM manifests as computer instability and you can just replace RAM without data loss, as nobody is permanently storing data in RAM

Because the data spends so much longer on disk than in RAM, the chance of a bit flip affecting stored data.

aaaaaaaaaab7y ago

It takes bad luck for sure, but I once ruined a bunch (a big bunch) of my photos by syncing them to a NAS with a faulty RAM. It was a Synology Ds212 I think, back in 2012. Mind you, the device didn’t produce symptoms other than messing up regularly spaced bytes in the transferred files.

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jandrese7y ago

Yep, otherwise you aren't able to detect bit level errors unless they impact the metadata, and the metadata is a tiny fraction of your total storage.

That said, your hard drive already does block level checksumming so doing it at the FS layer is mostly redundant unless the errors are being introduced in your SATA controller or on the PCI bus.

aaaaaaaaaab7y ago

You would still need end-to-end integrity checking, unless your Mac came with ECC memory (which it probably didn't).

mcpherrinm7y ago

Memory errors are still a concern, however, RAM is not used for persistent storage.

If a bit flip occurs during the path to storing data, that could get persisted. That's a moment in time, though. Maybe you'll notice the document you just wrote seems corrupted, or just has a typo.

Because the data spends so much longer on disk than in RAM, the chance of a bit flip affecting stored data.

aaaaaaaaaab7y ago

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