3 ms·

To do error correction you need more bits than when you only need to detect errors. With hard disks, error correction is done by adding a CRC code [0] (or some

To do error correction you need more bits than when you only need to detect errors. With hard disks, error correction is done by adding a CRC code [0] (or something similarly short) to each block, so that when the device reads a block and the CRC check fails it can be fairly certain that that block isn't performing well anymore and stop using it. SSD's behave differently as far as I know but there's a similar mechanism in use. To be able to not only detect errors but also correct the data you need more bits of error correction information. Offering up bits to store error correction information isn't worth the penalty of not having those bits available to store data in a lot of cases. [0] https://en.wikipedia.org/wiki/Cyclic_redundancy_check https://en.wikipedia.org/wiki/Cyclic_redundancy_check

blattimwind 8y ago
> With hard disks, error correction is done by adding a CRC code [0] (or something similarly short) to each block, so that when the device reads a block and the CRC check fails it can be fairly certain that that block isn't performing well anymore and stop using it. SSD's behave differently as far as I know but there's a similar mechanism in use. > To be able to not only detect errors but also correct the data you need more bits of error correction information. Offering up bits to store error correction information isn't worth the penalty of not having those bits available to store data in a lot of cases. Hard disks use forward error correction to make more effective use of the medium; the "medium" being a noisy channel means that using FEC to inflate the data but be able to recover from errors means you can perform much MUCH better on the BER/bandwidth front [increasing "bandwidth" of the "channel" means more data stored] than naively storing data. That's why everyone is doing it. Same goes for SSDs. The 520 byte sector approach is/was still used, but it is not the physical layer of hard disks and hasn't been for ... an unsigned long long time.
- BurnGpuBurn 8y ago
  I didn't know that, I thought those techniques were only used in data transmission over wired or wireless network connections. Thanks for the heads up.

blattimwind 8y ago

> With hard disks, error correction is done by adding a CRC code [0] (or something similarly short) to each block, so that when the device reads a block and the CRC check fails it can be fairly certain that that block isn't performing well anymore and stop using it. SSD's behave differently as far as I know but there's a similar mechanism in use. > To be able to not only detect errors but also correct the data you need more bits of error correction information. Offering up bits to store error correction information isn't worth the penalty of not having those bits available to store data in a lot of cases. Hard disks use forward error correction to make more effective use of the medium; the "medium" being a noisy channel means that using FEC to inflate the data but be able to recover from errors means you can perform much MUCH better on the BER/bandwidth front [increasing "bandwidth" of the "channel" means more data stored] than naively storing data. That's why everyone is doing it. Same goes for SSDs. The 520 byte sector approach is/was still used, but it is not the physical layer of hard disks and hasn't been for ... an unsigned long long time.

BurnGpuBurn 8y ago
I didn't know that, I thought those techniques were only used in data transmission over wired or wireless network connections. Thanks for the heads up.