Does ECC RAM Protect an External HDD?

[Thunderbird]

With the iMac Pro having ECC memory, it made me wonder about something: If you attach an external HDD to the iMac Pro, does the ECC RAM also protect the data on the disk in an external enclosure? Are external drives considered part of the same system the RAM uses? Or is the RAM only applicable to what's inside the iMac Pro itself?

 

[jerwin]

ECC ram uses parity calculations to detect and prevent single bit errors in RAM. ECC RAM does not prevent errors on the the SSD, nor any hard drive. (nor even, iirc, the RAM on the graphics card.) There are RAID configurations that are analogous to ECC memory--RAID 5 and 6 come to mind. (RAID 0 is not fault tolerant, but it is fast)



see
https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_5
https://en.wikipedia.org/wiki/ECC_memory

(Note that fault tolerant RAID arrays take a very long time to rebuild after a drive failure (1-2 days per terabyte)-- and if another drive fails during the rebuild, you're pretty much sunk-- which sort of makes the whole concept obsolete.

 

[Thunderbird]

Thanks. But when working with data on an external drive, RAM is still being used, correct?

It made me wonder if NAS devices would need to have ECC RAM, if they are already connected to computers with ECC memory. I'm trying to decide whether to get a NAS, or just go with an external HDD, and how ECC memory figures into my decision.

 

[mpe]

Having ECC RAM never hurts. RAM could be used for memory-mapped files or as a file cache. So in rare cases, flipping a bit wit that happens to be a part of dirty file system data in RAM, then having ECC RAM can avoid corruption.

But it is far more likely that data on disk drives gets corrupted by something else than RAM errors (file system corruption, software error, process crashes, SSD cell errors, media errors). So I wouldn't say that ECC protects external hard drives.