Re:Why Use ECC Memory
by hi-v-rocknroll on Wednesday May 08, 2024 @06:09AM
(#40296228)
I would wager 99.99% of bitrot is silent corruption that goes unnoticed until it affects something particularly important. Without integrity and error correction in all paths along a processor, storage hierarchy, and network paths and at rest, there's no way to prove a system will ever remain reliable.
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The network level is usually pretty solid in that regard, with checksumming at wifi/Ethernet protocol level and at tcp, but that's the end of it for most systems.
TCP checksums are very basic. Ethernet has a proper CRC, which at least has certain mathematical guarantees about what it can detect. The TCP checksum fails if the same bit is flipped from 0 to 1 and 1 to 0 in the same bit position modulo 16.
modulo 16 really? I thought it is modulo 2^16-1 (size of multiplicative group of GF(2^16)) which is much bigger than typical packet size
The TCP checksum is based on the sum of all odd bytes and the sum of all even bytes. Adding a power of 2 to an odd byte and subtracting the same power from another odd byte will cancel out. I'm not sure what guarantees CRC-32 gives you, but they're better than that.